Paleoexhibit

One big Triassic land predator: Erythrosuchus africanus

2015-04-12T12:54:00.000-07:00

Reconstruction of Erythrosuchus africanus. CZJ posing as scale.

When it comes to ferocious prehistoric land carnivores, there is one group that never did get much attention outside paleontological circles and it is likely that you never heard of them: the erythrosuchids. This is a pity because, as far as we know, Erythrosuchus africanus was the largest land predator in South Africa during the Middle Triassic period. At an estimated total body length of 5 meters, it possessed a massive one meter long skull equipped with numerous sharp conical teeth, superficially resembling that of big meat eating dinosaurs such as Tyrannosaurus rex. The head was thus disproportionately large with respect to the rest of the body. Unlike T-rex however, Erythrosuchus was quadrupedal, stalking preys on its rather short limbs. The limbs had a semi-erect posture, making it a more efficient runner than most of its contemporaries. Early representations of Erythrosuchus show it with a deep tall snout but modern reconstructions based on the discovery of a complete skull, indicate that it had a more tapered face similar to other erythrosuchids.

The creature has been first described by Scottish paleontologist Robert Broom in 1905 from fragmentary and poorly preserved remains (on a side note, Broom became famous for his later discoveries of early hominid fossils including Paranthropus robustus). Erythrosuchus (the name means “Red crocodile”) is today known from a number of specimens all relatively incomplete but enough to provide a good picture on what the animal may have looked like in real life. All the fossils were unearthed from the upper layers of the so called “Cynognathus assemblage zone”, Upper Beaufort Series, of the Karoo basin of South Africa and date from the Early Middle (Anisian) Triassic period (~245 MYA). Erythrosuchus was therefore contemporary with the cynodonts Cynognathus, Diademodon and Trirachodon and the large plant-eating dicynodont Kannemeyeria, the latter representing its main meal in all probabilities. Other representatives of the Cynognathus assemblage zone fauna are the small theriodont Bauria, the agile archosauriforme Euparkeria, the early rhynchosaurs Howesia and Mesosuchus and the big capitosauroid amphibians such as Watsonisuchus.

The erythrosuchids represent the first radiation of large terrestrial carnivores within the Archosauriformes. They were not quite archosaurs (the higher clade that includes crocs, dinosaurs and birds) but very close relatives. Erythrosuchids appeared in the late Early Triassic period and survived to the end of the Middle Triassic period and had likely a worldwide distribution. Erythrosuchus was the largest among them. The most primitive erythrosuchid is the medium-sized long snouted Fugusuchus hejiapensis from the Heshankou formation (Olenekian) of the Shanxi province of China. Others representatives include Garjainia prima from the Yarenskian horizon (Olenekian) of the Orenburg region of Russia, Vjushkovia triplicostata and Uralosaurus magnus both from the Donguz Formation (Anisian) of the Orenburg region of Russia, Shansisuchus shansisuchus and Guchengosuchus shiguaiensis, both from the upper Ermaying Formation (Anisian) of the Shanxi Province of China. Chalishevia cotburnata from the Bukobay Formation (Ladinian) of the Orenburg region of Russia, is the last known member of the group. It is conjectured that the erythrosuchids went extinct because they were outcompeted in their ecological niche by more efficient archosaurian predators such as the Rauisuchians.

References:

Cruickshank, A. R. I. (1978). The pes of Erythrosuchus africanus Broom. Zoological Journal of the Linnean Society, 62(2), 161-177.

Gower, D. J. (1997). The braincase of the early archosaurian reptile Erythrosuchus africanus. Journal of Zoology, 242(3), 557-576.

Gower, D. J. (2001). Possible postcranial pneumaticity in the last common ancestor of birds and crocodilians: evidence from Erythrosuchus and other Mesozoic archosaurs. Naturwissenschaften, 88(3), 119-122.

Parrish, J. M. (1992). Phylogeny of the Erythrosuchidae (Reptilia: Archosauriformes). Journal of Vertebrate Paleontology, 12(1), 93-102.

Were dinosaurs responsible for their own demise by initiating a runaway climate change?

2015-04-01T01:00:00.000-07:00

Many scenarios have been put forward to explain the sudden disappearance in the fossil record of all non-avian dinosaurs, along with many other group of animals such as plesiosaurs, mosasaurs, ammonites and pterosaurs, at the very end of the Cretaceous period, 65 million years ago. Explanations such as starvation due to the rise of flowering plants that their stomach could not process, epidemic diseases of planetary proportion or loss of genetic diversity have long been discarded by scientific evidences. Today, most scientists adhere to the idea of a catastrophic event that caused global devastation of such magnitude many group of animals were unable to cope with. A large crater off the Yucatan peninsula (the Chicxulub crater) is believed to be the site of a massive asteroid/comet impact that wiped out the dinosaurs and 75% of life on Earth (Hildebrand et al., 1991). More recently, the Deccan traps theory, volcanic activity of unprecedented scale on the Indian subcontinent, gained ground when precise dating of the event shows it happened just before the so called K-Pg (Cretaceous-Paleogene) boundary (Schoene et al., 2015). A more exotic theory proposed dark matter in our galaxy as the prime culprit for the deed (Rampino, 2015).

However, in a new study that has just been published in the Journal of Supernatural Geological Studies, Dr. A. Zierste and co-workers came up with another plausible explanation (Zierste et al., 2015). It is well known that the Earth went through an episode of extreme “global warming” with high level of greenhouse gases during the Paleocene and Eocene periods of the Tertiary that followed the Cretaceous. The famous “Messel pit” in Germany with its exceptionally well preserved fossils of a rich tropical and subtropical fauna and flora is a vivid testimony of what the climate was at this high latitude. Zierste wondered about the mechanism that caused this greenhouse effect. Using a Tunable laser Spectrometer (TLS) similar to the one employed by the Mars Curiosity Mission (Webster et al., 2015), her team measured with high precision the isotopic ratio of light elements such as carbon and oxygen contained in sedimentary rocks from the end of the Cretaceous period to the beginning of the Eocene period. The data indicate a gradual increase in methane and carbon dioxide levels in the atmosphere that peaked right at the K-Pg boundary. But what is the origin of the high level of greenhouse gases? Zierste has a surprising answer to it: dinosaurs! These beasts were reaching gigantic proportions by the end of the Jurassic. The long-necked sauropods in particular were truly titanic, with some individuals attaining an estimated weight of 100 tons. To sustain their body mass, they have to eat tremendous amount of plants. Their stomachs were formidable fermentation chambers, producing colossal amount of methane gas that were naturally released in the Mesozoic atmosphere through gastric emanations. Methane is actually 20 times better at trapping heat than carbon dioxide. A 2006 United Nations' Food and Agricultural Organization report (http://www.fao.org/ag/magazine/0612sp1.htm ) has shown that the some 1.5 billion cows bred for milk and meat by the human population on Earth today have a non-negligible contribution to the current climate change, generating 18% more greenhouse gas than transport, in CO2 equivalent unit. Now imagine the amount of methane gas that dinosaurs could have produced. Bone histology studies have shown that the biggest dinosaurs lived to very old age, maybe 100 years and their population were most probably quite large, as they were social animals living in herds. It is difficult to estimate the total population of dinosaurs that lived on Earth at any moment of time during the Mesozoic but Zierste and her colleagues using a conservative number of about 1 billion sauropods and hadrosaurs calculated that they would have generated a staggering 20 billion metric tons of methane per year, enough to provoke a fast climate change and rapid rise of the Earth atmospheric temperature. In other words, dinosaurs perished because they induced a runaway global warming triggered by their own flatulence. Without the asteroid impact, that put an end to the continuous rise in temperature by provoking a global cooling, it is likely that the remaining 25% species of animals and plants would also have vanished and we would not be around to tell the tale.

References:

Avril Z., Peter S. G., Robert T. B., Ines L. P., Lambert J. B., Stewart M.T., Fernando E. N., Oviedo T. F., Oscar J., Lewis C. C. (2015) Geochronological correlation of NH4 level with global atmospheric temperature at the Cretaceous/Paleogene boundary. J. of Supernatural Geological Studies, 90., 1-12.

Hildebrand, A. R., Penfield, G. T., Kring, D. A., Pilkington, M., Camargo, A., Jacobsen, S. B., & Boynton, W. V. (1991). Chicxulub crater: a possible Cretaceous/Tertiary boundary impact crater on the Yucatan Peninsula, Mexico. Geology, 19(9), 867-871.

Rampino, M. R. (2015). Disc dark matter in the Galaxy and potential cycles of extraterrestrial impacts, mass extinctions and geological events. Monthly Notices of the Royal Astronomical Society, 448(2), 1816-1820.

Schoene, B., Samperton, K. M., Eddy, M. P., Keller, G., Adatte, T., Bowring, S. A., ... & Gertsch, B. (2015). U-Pb geochronology of the Deccan Traps and relation to the end-Cretaceous mass extinction. Science, 347(6218), 182-184.

Webster, C. R., Mahaffy, P. R., Atreya, S. K., Flesch, G. J., Mischna, M. A., Meslin, P. Y., ... & Lemmon, M. T. (2015). Mars methane detection and variability at Gale crater. Science, 347(6220), 415-417.

Dickinsonia from the Ediacara biota

2015-02-08T12:26:00.000-08:00

Reconstruction of Dickinsonia costata

In 1946, while investigating abandoned mines in the Ediacara Hills, South Australia, geologist Reginald Claude Sprigg stumbled upon some peculiar and barely visible trace fossils of jellyfish-like creatures. He realized that they must be far older than any fossil known at the time. He published his preliminary results in the Transactions of the Royal Society of South Australia (1947, 1948). He then tried to publish his findings in the prestigious journal Nature and made a presentation at the 1948 International Geological Congress, but his results were largely dismissed by the larger scientific community. Sprigg will have to wait until 1959 for his contribution to be recognized when paleontologist Martin Glaessner evaluated the age of the Ediacaran rocks to be Precambrian (~600 MYA) and fully appreciated the importance of the fossils found within. The Ediacara biota consists of a number of truly enigmatic trace fossils of soft bodied creatures that give us a glimpse of what life forms existed before the evolutionary “invention” of readily fossilizable parts such as hard shells.

Spriggina, another enigmatic creature from the Ediacara biota

One of the most famous fossils of the Ediacara biota is Dickinsonia, first described by Sprigg in 1947. Dickinsonia fossils were preserved as imprints of ovoid or ribbon- like creatures with bilateral symmetry. Their sizes range from a few millimeters to practically a meter in length. The animal also appeared to be segmented. The affinities of Dickinsonia were and is, still today, highly debated. Is it related to jellyfish (Sprigg, 1947) , corals (Valentine, 1992), comb jellies (Zhang & Reitner, 2006)? Is it a lichen (Retallak, 1994, Retallak, 2007), a sponge, a polychaete worm (Wade, 1972), a giant single cell organism (Seilacher et al., 2003) or something else altogether? In the absence of any discernable proof of affiliation to any modern phylum, a brand new name was erected to encompass these strange precambrian fossils, the Vendobionta (Seilacher,1992; Buss & Seilacher, 1994), that would have evolved before the reign of the eumetazoans (all bilateral animals plus the cnidaria [jellyfish, coral, sea anemones, …] and ctenophores [comb jellies]). The phylum Vendobionta regroups many of the familiar Ediacaran fossils such as Dickinsonia, Spriggina, and Charnia, and they are viewed as immobile creatures, possibly ancestral to the Cnidaria. Some authors have argued that Dickinsonia like other Ediacaran fauna (such as the above mentioned Spriggina) lacked true bilateral symmetry and placed them in a phylum called Proarticulata (Fedonkin, 1987; Fedonkin, 2003) that went totally extinct at the end of The Precambrian and left no descendant. Specimens of Dickinsonia indeed show that the segments do not join symmetrically at the median ridge but are made of portions called isomers that alternate along the longitudinal axis, as if one side of the body is shifted by half a segment period with respect to the other half.

Charnia looked like modern sea pens but they were
probably unrelated.

However extensive examination of hundreds of specimens show that the lack of bilateral symmetry in those individuals is only apparent and is, like the presence of the middle line rim, a preservation artifact (Gehling et al., 2005). Dickinsonia was thus a true bilateral segmented creature. Specimens showing folds and tears also indicate that it was a soft-bodied flexible organism, contradicting earlier claims that only rigid "wood-like" bodies could have been preserved in sandstone (Retallak, 1994). The preservation of series of oval traces “following” the body mold of some Dickinsonia specimens, that are about the same size and shape as the animal itself, also indicates that it was clearly mobile, so the hypothesis of its affinity to a phylum such as sponges or lichens with a sessile life can be rejected. These traces have been interpreted as resting or feeding traces, imprints of shallow depressions left by Dickinsonia as it fed and digest the layer of organic matter underneath. The total absence of anything that look like a digestive system such as a mouth (Gehling et al., 2005) indicates that the animal was most probably feeding through ventral external digestion. And there is actually only one phylum of animals alive today that eats in this way, the Placozoans. So, is Dickinsonia a placozoan (Sperling & Vinther, 2010)? The difficulty of this hypothesis is that modern placozoans,such as Trichoplax adhaerens, appear to be much simpler creatures. Although multicellular, they do look like amoebas, with no apparent bilateral symmetry, no segments and reproduced asexually by budding. However, the genome sequencing of Trichoplax (Srivastava et al., 2008) showed that they belong to the eumetazoans. Cnidarians (jellyfish, sea anemones, corals and the like) do possess a radial symmetry rather than a bilateral symmetry. However molecular and deep morphological clues reveal that cnidarians were originally bilateral (Matus et al., 2006). Thus bilaterality was probably an ancestral feature to all eumetazoans including placozoans. So is Dickinsonia a placozoan? Well, we still can’t say for sure and the debate is far from closed, but that's one definite intriguing possibility.

Acknowledgment: I am indebted to Prof. James G. Gehling who has kindly provided me with first-hand information about Dickinsonia.

References:

Buss, L. W., & Seilacher, A. (1994). The Phylum Vendobionta: a sister group of the Eumetazoa?. Paleobiology, 1-4.

Fedonkin, M. A. (1987). Non-skeletal fauna of the Vendian and its place in the evolution of metazoans. Trans. Paleontol. Inst., 226. Nauka, Moscow 175 pp. (in Russian).

Fedonkin, M. A. (2003). The origin of the Metazoa in the light of the Proterozoic fossil record. Paleontological Research, 7(1), 9-41.

Gehling, J. G., Droser, M. L., Jensen, S. R., & Runnegar, B. N. (2005). Ediacara organisms: relating form to function. Evolving form and function: fossils and development, 43-66.

Matus, D. Q., Pang, K., Marlow, H., Dunn, C.W., Thomsen, G. H., and Martindale, M. Q. (2006). Molecular evidence for deep evolutionary roots of bilaterality in animal development. Proc. Natl. Acad. Sci., USA 103: 1195–1120.

Retallack, G. J. (1994). Were the Ediacaran fossils lichens?. Paleobiology, 523-544.

Retallack, G. J. (2007). Growth, decay and burial compaction of Dickinsonia, an iconic Ediacaran fossil. Alcheringa, 31(3), 215-240.

Seilacher, A. (1992). Vendobionta and Psammocorallia: lost constructions of Precambrian evolution. Journal of the Geological Society, 149(4), 607-613.

Seilacher, A., Grazhdankin, D., and Legouta, A. (2003). Ediacaran biota: the dawn of animal life in the shadow of giant protists. Paleontol. Res. 7: 43– 54.

Sperling, E. A., & Vinther, J. (2010). A placozoan affinity for Dickinsonia and the evolution of late Proterozoic metazoan feeding modes. Evolution & development, 12(2), 201-209.

Srivastava, M., Begovic, E., Chapman, J., Putnam, N. H., Hellsten, U., Kawashima, T., ... & Rokhsar, D. S. (2008). The Trichoplax genome and the nature of placozoans. Nature, 454(7207), 955-960.

Valentine, J. W. (1992). Dickinsonia as a polypoid organism. Paleobiology, 378-382.

Wade, M. (1972). Dickinsonia: polychaete worms from the late Precambrian Ediacara fauna, South Australia. Memoirs of the Queensland Museum, 16(2), 171-190.

Zhang, X., & Reitner, J. (2006). A fresh look at Dickinsonia: removing it from Vendobionta. Acta Geologica Sinica (English Edition), 80(5), 636-642.

First among the synapsids: the ophiacodonts

2015-01-31T17:29:00.000-08:00

The synapsids constitute the second major group of reptiles after the diapsids. They are characterized by a single hole in the skull just behind each eye socket called temporal fenestrae. Synapsids include the mammals (thus including us), their reptilian ancestors (“mammal-like reptiles”) and all their closest extinct relatives . The oldest known synapsid belongs to a group called Ophiacodontids which flourished during the Late Carboniferous and Early Permian periods. These were a rather peculiar lot with their unusually large head compared to their body size. The skull was very tall and narrow. The slightly recurved teeth were sharp, numerous and tightly packed inside the jaws, two being a bit larger than the other forming the upper canines. These medium size animals were among the largest land carnivores of their time. The limbs were rather short, broad and bulky.

Archaeothyris florensis

The ancestral ophiacodontid type can be seen in Archaeothyris florensis (Reisz, 1972) from the Late Carboniferous of Nova Scotia, Canada (Westphalian C; 308-311 MYA), which is by the way, the earliest known definite synapsid. It somewhat looked like a modern lizard but with already the group hallmark of a tall and elongated skull. Measuring about 50 cm, it was contemporary to other early reptiles such Palaeothyris and living in a swampy forest made of giant tree-like lycopsids (club mosses) and dominated by amphibians and giant arthropods.

Varanosaurus acutirostris (Broili, 1904) from the Early Permian of Texas, measured about 1.2 m in length and was an agile predator with a slender laterally compressed snout. It is known from decent material including the almost complete holotype skeleton. A second species, V. wichitaensis, has been described, based on isolated postcranial remains (Romer, 1937) and is virtually indistinguishable from V. acutirostris besides being smaller and geologically slightly older.

Varanosaurus acutirostris

Body proportions reached its extremes in Ophiacodon (Marsh, 1878; Cope, 1878; Case, 1907; Romer, 1925; Romer & Price, 1940) the best known and most studied ophiacodont. Many skeletons of this odd-looking animal are known from the Early Permian of Texas, New Mexico, Kansas, Oklahoma, Colorado, Utah and Ohio and it is unclear how many of the described species are actually valid. For the story, the type species, Ophiacodon mirus was first described by Othniel Marsh in 1878 based on a mandible and vertebrae in the midst of the so-called “bone war” against his rival Edwin Cope. Marsh clearly intended to beat Cope, who had a paper in press, in the naming of this animal but his hastily written paper was so deficient that the name Ophiacodon was ignored by the paleontological community for over 30 years. In the meantime, Cope’s paper published just days after Marsh’s, described three species, Theropleura retroversa, T. uniformis and T. triangulata, based on isolated vertebrae. The type specimen of Ophiacodon was reinvestigated by Williston and a new complete skeleton described in the 1910s (Williston & Case, 1913) and it is much later that Theropleura was found to be synonymous with Ophiacodon although the species names were retained (Romer & Price, 1940). The following species are still recognized today: O. mirus, known from several skeletons including a nearly complete one from New Mexico and Oklahoma; O. retroversus, known from multiple materials from Texas and Oklahoma, including a near complete skelton; O. uniformis from several partial skeletons from Texas and Oklahoma; O. navajonicus frong fragmentary postcranial skeletons from New Mexico; O. hilli known from a fragmentary skeleton from Kansas; O. major from fragmentary materials from Texas. It appears that size difference might reflect different growth stage rather than species (Brinkman, 1988). Ophiacodon was originally thought to be a semi-aquatic animal but recent studies debunked all the supposed aquatic adaptation that the animal might have possessed and today (Felice & Angielczyk, 2014), Ophiacodon is viewed as a fully terrestrial predator. Specimens of Ophiacodon have sizes ranging from 1.5 m up to 3 m in length.

Ophiacodon mirus

Other ophiacodontids are known from rather fragmentary remains and include the Late Carboniferous genera Clepsydrops and Echinerpeton from North America and Stereorhachis from France, the Early Permian Stereophallodon, Baldwinonus from North America. Protoclepsydrops haplous (Carrol, 1964) from Nova Scotia might also have been an ophiacodontid predating Archaeothyris but the remains are so fragmentary that it is difficult to tell for sure.

Refrerences:

Brinkman, D. (1988). Size-independent criteria for estimating relative age in Ophiacodon and Dimetrodon (Reptilia, Pelycosauria) from the Admiral and lower Belle Plains formations of west-central Texas. Journal of Vertebrate Paleontology, 8(2), 172-180.

F. Broili. 1904. Permische Stegocephalen und Reptilien aus Texas. Palaeontographica 51:1-120

Carroll, Robert L. (1964). "The earliest reptiles". Journal of the Linnean Society of London, Zoology 45 (304): 61–83

E. C. Case. 1907. Revision of the Pelycosauria of North America. Carnegie Institution of Washington 55:3-176

E. D. Cope. 1878. Descriptions of extinct Batrachia and Reptilia from the Permian formations of Texas. Proceedings of the American Philosophical Society 17:505-530

Felice, R. N., & Angielczyk, K. D. (2014). Was Ophiacodon (Synapsida, Eupelycosauria) a swimmer? A test using vertebral dimensions. In Early evolutionary history of the Synapsida (pp. 25-51). Springer Netherlands.

R. R. Reisz. 1972. Pelycosaurian Reptiles from the Middle Pennsylvanian of North America. Bulletin of the Museum of Comparative Zoology 144(2):27-60

A. S. Romer. 1925. An ophiacodont reptile from the Permian of Kansas. Journal of Geology 33(2):173-182

A. S. Romer. 1937. New genera and species of pelycosaurian reptiles. Proceedings of the New England Zoölogical Club 16:89-95

A. S. Romer and L. I. Price. 1940. Review of the Pelycosauria. Geological Society of America Special Paper 28:1-538

Williston, S. W., & Case, E. C. (1913). Description of a nearly complete skeleton of Ophiacodon Marsh. Carnegie Institution of Washington Publication, 181, 37-59.

2014 in Paleontology

2014-12-30T19:18:00.000-08:00

Here are my picks for the top paleontology stories of year 2014 (not in particular order):

1) Fossilized pigments show mesozoic marine reptiles in their true colors.

Tylosaurus nepaeolicus

Ref: Lindgren, J., Sjövall, P., Carney, R. M., Uvdal, P., Gren, J. A., Dyke, G., ... & Polcyn, M. J. (2014). Skin pigmentation provides evidence of convergent melanism in extinct marine reptiles. Nature. 506, 484–488.

2) Copulation and internal fertilization have appeared 385 millions years ago in primitive armored fish adding a big step to our understanding of the evolution of sex in our distant ancestors.

Ref: Long, J. A., Mark-Kurik, E., Johanson, Z., Lee, M. S., Young, G. C., Min, Z., ... & Trinajstic, K. (2014). Copulation in antiarch placoderms and the origin of gnathostome internal fertilization. Nature. Published online

3) New fossils of the cambrian chordate Metaspriggina walcotti show that it was an early very primitive fish.

Metaspriggina walcotti

Ref: Morris, S. C., & Caron, J. B. (2014). A primitive fish from the Cambrian of North America. Nature, 512(7515), 419-422.

4) Exceptionally well preserved fossilized eye tissues of a 300 millions years old spiny shark, Acanthodes bridgei, shows it had color vision.

Acanthodes sp.

Ref: Tanaka, G., Parker, A. R., Hasegawa, Y., Siveter, D. J., Yamamoto, R., Miyashita, K., ... & Maeda, H. (2014). Mineralized rods and cones suggest colour vision in a 300 Myr-old fossil fish. Nature Communications, 5, 5920.

5) Spinosaurus was an odd-looking semi-aquatic predator that might have walked on all four.

Ref: Ibrahim, N., Sereno, P. C., Dal Sasso, C., Maganuco, S., Fabbri, M., Martill, D. M., ... & Iurino, D. A. (2014). Semiaquatic adaptations in a giant predatory dinosaur. Science, 345(6204), 1613-1616.

Deinocheirus mirificus

Spinosaurus aegyptiacus

6) Two new fossils of Deinocheirus mirificus solved 44 years old “terror arms” mystery.

Ref: Lee, Y. N., Barsbold, R., Currie, P. J., Kobayashi, Y., Lee, H. J., Godefroit, P., ... & Chinzorig, T. (2014). Resolving the long-standing enigmas of a giant ornithomimosaur Deinocheirus mirificus. Nature. 515, 257–260.

Dreadnoughtus schrani

7) Dreadnoughtus schrani, one of the largest dinosaurs and the most complete skeleton of a titanosaur to have been discovered to date.

Ref: Lacovara, K. J., Lamanna, M. C., Ibiricu, L. M., Poole, J. C., Schroeter, E. R., Ullmann, P. V., ... & Novas, F. E. (2014). A Gigantic, Exceptionally Complete Titanosaurian Sauropod Dinosaur from Southern Patagonia, Argentina. Scientific reports, 4, 6196.

Kulindadromeus zabaikalicus

8) The discovery of the feathered ornithischian Kulindadromeus zabaikalicus, suggests that the earliest dinosaurs probably also sported feathers.

Ref: Godefroit, P., Sinitsa, S. M., Dhouailly, D., Bolotsky, Y. L., Sizov, A. V., McNamara, M. E., ... & Spagna, P. (2014). A Jurassic ornithischian dinosaur from Siberia with both feathers and scales. Science, 345(6195), 451-455.

Vintana sertichi

9) The discovery of a complete skull of Vintana sertichi shed light on an obscure group of mammals called Gondwanatheres previously reported from teeth and jaw fragments only.

Ref: Krause, D. W., Hoffmann, S., Wible, J. R., Kirk, E. C., Schultz, J. A., von Koenigswald, W., ... & Andriamialison, H. (2014). First cranial remains of a gondwanatherian mammal reveal remarkable mosaicism. Nature, 515(7528), 512-517.

Atopodentatus unicus

10.- Atopodentatus unicus is probably one of the strangest vertebrate fossil ever found.

Ref: Cheng, L., Chen, X. H., Shang, Q. H., & Wu, X. C. (2014). A new marine reptile from the Triassic of China, with a highly specialized feeding adaptation. Naturwissenschaften, 101(3), 251-259.

Semirostrum cerrutii

11.- A fossil porpoise, Semirostrum cerrutii, reveals unique skim feeding habit.

Ref: Racicot, R. A., Deméré, T. A., Beatty, B. L., & Boessenecker, R. W. (2014). Unique Feeding Morphology in a New Prognathous Extinct Porpoise from the Pliocene of California. Current Biology, 24(7), 774-779.

12.- A massive genomic analysis on 44 species of birds representing all extant orders resolves bird tree-of-life and ancestry. Chickens and turkeys, it turns out, were found to be more closer to their dinosaur ancestors than any other birds.

Ref: Jarvis, E. D., Mirarab, S., Aberer, A. J., Li, B., Houde, P., Li, C., ... & Samaniego, J. A. (2014). Whole-genome analyses resolve early branches in the tree of life of modern birds. Science, 346(6215), 1320-1331.

Extraordinary Tanystropheus

2014-11-03T19:55:00.003-08:00

Tanystropheus longobardicus reconstructed as a shoreline fish hunter.

With a length approaching 5 meters for the largest specimens, half of which taken up by an extremely elongated neck, Tanystropheus was a truly remarkable creature. The neck was quite rigid being made of only a dozen of elongated cervical vertebrae. The behavioral habit of Tanystropheus has been intensely debated and the exact function of such a neck still constitutes to this day a puzzling enigma. At first, and based on fragmentary and disarticulated remains from Germany, Tanystropheus was thought to be a flying reptile (Nopsca 1923). Later, when more complete and articulated fossils have been discovered in the Alps, it was viewed as a terrestrial lizard-like creature that hunted fish from the shoreline, using its neck to reach out long distances (Peyer, 1931). Still, a later study found that the neck was probably too rigid to be flexed above shoulder level forcing it to an horizontal position, therefore making a fully aquatic lifestyle more probable (Tschanz, 1986). However, it was argued that Tanystropheus’s skeleton does not show any obvious sign of aquatic adaptation and the limbs were ill-suited for paddling, so the question of how this animal could have swam in open water makes the hypothesis problematic. A new specimen from Switzerland with preserved skin and soft tissue impressions (Renesto, 2005) shows a large amount of fleshy part in the tail which would have acted as an efficient counterweight to the neck making it possible for the animal to moved it up. This last study makes Peyer’s hypothesis of a semi-aquatic animal staying on the shoreline and using its long neck to reach out for fish farther in the water more likely but the debate is certainly far from being closed (Nosotti, 2007).

Tanystropheus belongs to a small group of basal archosauromorphs (the group that contains all archosaurs such as crocs, dinos and birds) called protorosaurs. Some well known members of this group of Late Permian to Late Triassic animals include Protorosaurus speneri from the Late Permian of Germany, the “monkey lizard” Drepanosaurus unguicaudatus and Megalancosaurus preonensis of the Late Triassic of Italy, and Tanystropheus. Several species of Tanystropheus have been described, probably not all valid. The type species, T. conspicuus Meyer, 1855 from the Middle Triassic (Anisian) Upper Muschelkalk of Germany is known from very fragmentary material. The most completely and best known species is T. longobardicus (Bassani, 1886) for which many specimens, some quite complete, adults and juveniles from the Middle Triassic Besano Formation of Italy were found. Specimens from the Monte San Giorgio in Switzerland have been referred to this species, as well as one specimen from the Falang Formation of the Guizhou province of China (Rieppel et al., 2010). The latter confirms the close faunal connection between the western side of the Tethys sea (Europe) and its eastern border (China) during the Middle Triassic period. T. meridensis Wild, 1980 is known from a single incomplete specimen from the Meride Limestome, Monte San Girogio, Switzerland, but this one is probably a junior synonym of T. longobardicus. T. haasi Rieppel, 2001 from the Middle Triassic Muschelkalk of Israel has been described based on cervical vertebrae.

Tanystropheus forms with all its closest long-necked relatives the family Tanystropheidae. These include Amotosaurus rotfeldensis Fraser & Rieppel, 2006 from the Middle Triassic (Upper Buntsandstein) of Germany, the recently described and oldest member of the group, Augustaburiania vatagini Sennikov, 2011 from the Early Triassic of the Don River, Volgograd Region, Russia, Protanystropheus antiquus (Huene, 1905) from the Middle Triassic (Lower Muschelkalk, Gogolin Formation, Anisian) of Poland, Tanytrachelos ahynis Olsen, 1979 from the Late Triassic (Cow Branch Formation, Newark Supergroup) of North Carolina and Virginia , and Dinocephalosaurus orientalis Li, 2003 from the Middle Triassic (Guanling Formation) of the Guizhou province of China. Some authors also include the bizarre Langobardisaurus Renesto, 1994 from the Late Triassic (Zorzino Limestone Formation) of Italy.

References:

Fraser, N., & Rieppel, O. (2006). A new protorosaur (Diapsida) from the Upper Buntsandstein of the Black Forest, Germany. Journal of Vertebrate Paleontology, 26(4), 866–871.

Nosotti, S. (2007). " Tanystropheus Longobardicus"(Reptilia, Protorosauria): Re-interpretations of the Anatomy Based on New Specimens from the Middle Triassic of Besano (Lombardy, Northern Italy). Società Italiana di Scienze Naturali e Museo Civico di Storia Naturale.

Peyer, B. (Ed.). (1931). Die Triasfauna der Tessiner Kalkalpen. 2. Tanystropheus longobardicus Bass. sp. Birkhäuser.

Renesto, S. (2005). A new specimen of Tanystropheus (Reptilia Protorosauria) from the Middle Triassic of Switzerland and the ecology of the genus. Rivista Italiana Di Paleontologia E Stratigrafia, 111(3), 377–394.

Rieppel, O. (2001). A new species of Tanystropheus (Reptilia: Protorosauria) from the Middle Triassic of Makhtesh Ramon, Israel. Neues Jahrbuch für Geologie und Paläontologie-Abhandlungen, 271-287.

Rieppel, O., Jiang, D., & Fraser, N. (2010). Tanystropheus cf. T. longobardicus from the early Late Triassic of Guizhou Province, southwestern China. Journal of Vertebrate Paleontology, 30(July), 1082–1089.

Tschanz, K. (1986). Funktionelle Anatomie der Halswirbelsäule von Tanystropheus Longobardicus (Bassani) aus der Trias (Anis, Ladin) des Monte San Giorgio (Tessin) auf der Basis vergleichend morphologischer Untersuchungen an der Halsmuskulatur rezenter Echsen. na.

Wild, R. (1980). Tanystropheus (Reptilia: Squamata) and its importance for stratigraphy. Mémoires de la Société Géologique de France NS, 139, 201-206.

Meet the Chroniosuchians

2014-09-01T22:16:00.003-07:00

Chroniosaurus dongusensis measured about 30 cm in length.

Chroniosuchians form a very obscure group of small, superficially croc-like four-legged animals that lived during the Late Permian period and survived until the Middle and perhaps Late Triassic periods. Most species are from the Late Permian (Late Tatarian regional stage) of Russia, but they are also known from China, Germany and Kyrgyzstan. They were aquatic or semi-aquatic fish-eating predators characterized by a distinct row of interconnected “butterfly-shaped” bony plates or scutes (osteoderms) covering their back and part of their tail, one for each vertebra. They are traditionally subdivided into two families, the more primitive Chroniosuchidae from the Late Permian with one representative in the Triassic and the Bystrowianidae from the Late Permian to the Middle Triassic. The exact affinities of the Chroniosuchians are quite uncertain. They are usually placed among non-amniote reptiliomorphs but more recent studies make them “stem tetrapods”, so not reptiles and not quite amphibians but something a bit more primitive. The eel-like embolomeres appear to have been their closest relatives.

Madygenerpeton pustulatus from Kyrgyzstan.

Among the Chroniosuchids, Chroniosaurus dongusensis Tverdochlebova, 1972 from the Late Permian of the Orenburg province of Russia is probably the best known species, with fossils from many individuals including one near complete articulated specimen. Chroniosuchus paradoxus Vjuschkov, 1957 also from the Orenburg province but a bit younger, differs in the taller shape of its skull. Madygenerpeton pustulatus Schoch et al., 2010 from the Middle or Late Triassic of Kyrgyzstan appears to be the basalmost member of the group despite its late occurrence. The type specimen is a nearly complete skull showing a broad snout quite different from the two previous species. Jarilinus mirabilis (Vjuschkov, 1957) from the Novgorod province and Uralerpeton tverdochlebovae Golubev, 1998 from the Vladimir Province were quite large species for the group, the reconstructed skull of the former measuring 20 cm and of the latter some 55 cm. The others three species, Chroniosaurus levis Golubev, 1908, Chroniosuchus lichaveri (Riabinin, 1962) and Suchonica vladimiri Golubev, 1999, all from the Vologda Province of Russia, are only known from fragmentary remains.

Chroniosuchus paradoxus.

The other family, the Bystrowianids, are much less known, their fossil remains consisting mainly on isolated armor scutes. Late permian species include Bystrowiana permira Vjuschkov, 1957 from the Vladimir Province of Russia, Bystrowiana sinica Young, 1979, Dromotectum largum Liu et al., 2014 and Jinyuanitectum flatum Liu et al., 2014, the last three from the Henan Province of China. Early Triassic species are Axitectum vjushkovi Shishkin & Novikov, 1992 from the Novgorod province, Axitectum georgi Novikov & Shishkin, 2000 from the Kirov province, Dromotectum spinosum Novikov & Shishkin, 1996 from the Orenburg Province. Middle Triassic forms are Synesuchus muravjevi Novikov & Shishkin, 2000 from the Komi Republic and Bystrowiella schumanni Witzmann et al., 2008 from Germany.

References:

Buchwitz, M., Foth, C., Kogan, I., & Voigt, S. (2012). On the use of osteoderm features in a phylogenetic approach on the internal relationships of the Chroniosuchia (Tetrapoda: Reptiliomorpha). Palaeontology, 55(3), 623–640.

Golubev, V. K. (1998). Narrow-armored Chroniosuchians from the Late Permian of Eastern Europe. Paleontological Journal, 32(3), 278–287.

Golubev, V. (1998). Revision of the Late Permian chroniosuchians (Amphibia, Anthracosauromorpha) from Eastern Europe. Paleontological Journal, 32(4), 390–401.

Golubev, V. K. (1999). A New Narrow-Armored Chroniosuchian from the Upper Permian of Eastern Europe. Paleontological Journal, 33(2), 166–173.

Klembara, J., Clack, J. a., & Čerňanský, A. (2010). The anatomy of palate of Chroniosaurus dongusensis (Chroniosuchia, Chroniosuchidae) from the Upper Permian of Russia. Palaeontology, 53(5), 1147–1153.

Liu, J., Xu, L., Jia, S.-H., Pu, H.-Y., & Liu, X.-L. (2014). The Jiyuan tetrapod fauna of the Upper Permian of China — 2 . stratigraphy , taxonomical review , and correlation. Vertebrata PalAsiatica, 52(3), 328–339.

Schoch, R., Voigt, S., & Buchwitz, M. (2010). A chroniosuchid from the Triassic of Kyrgyzstan and analysis of chroniosuchian relationships. Zoological Journal of the Linnean Society, 160, 515–530.

Witzmann, F., Schoch, R. R., & Maisch, M. W. (2008). A relict basal tetrapod from Germany: first evidence of a Triassic chroniosuchian outside Russia. Die Naturwissenschaften, 95(1), 67–72.

Dinosaurs of the British Isles: the Book

2014-07-20T17:08:00.000-07:00

For those of you who were wondering why I never completed my series on British dinosaurs on paleoexhibit, stopping midway through the theropods, here is the reason: the material has been used as a starting point for a book. Written in collaboration with Doncaster Museum very own paleontologist and good friend, Dean Lomax, the book has just been published by Siri Scientific Press and is available for purchase on Amazon (link from the ad on the left). Prefaced by Dr. Paul Barrett of the Natural History Museum, “Dinosaurs of the British isles” consists of over 400 pages describing in details some 100 species of dinosaurs unearthed for over two centuries in the United Kingdom. It features extensive amount of photographs of fossil remains taken by Dean as he visited all the major paleontology collections from England, Scotland and Wales, skeletal reconstructions from Scott Hartman, Jaime Headden and Greg Paul, as well as life reconstructions by talented artist James McKay, and by myself. Highly recommended to anybody interested in fossils in general, and British dinosaurs in particular.

Reference: D. R. Lomax & N. Tamura, 2014. “Dinosaurs of the British Isles”, Siri Scientific Press, 414 pages, ISBN 13: 9780957453050, ISBN 10: 0957453051

Two late Scottish relatives of Jamoytius

2014-05-21T13:28:00.000-07:00

Cornovichthys blaauweni.

The now flooded Achanarras fish beds in Caithness, Northern Scotland, has yielded an abundant collection of fossil fish belonging to some 15 genera dating from the Eifelian stage (about 390 MYA) of the Middle Devonian period. These include the arthrodire (a group of heavily armored jawed fish) Coccosteus cuspidatus, the Acanthodians (“spiny sharks”) Diplacanthus, Mesacanthus and Cheiracanthus, the enigmatic Palaeospondylus gunni, the early Actinopterygian (ray-finned fish) Cheirolepis treilli and the Sarcopterygians (lobed-finned fish) Osteolepis macrolepidotus and Dipterus valenciennesi. The agnathans (jawless fish) are a rarity there and consist of only two species, Cornovichthys blaaweni and Achanarella trewini, which are believed to be closely related to Jamoytius kerwoodi from the Silurian, and placed in the clade Jamoytiiforms. The limestone of Achanarras quarry has been deposited in what appear to have been a deep freshwater lake environment.

Cornovichthys blaauweni is known from a single carbonaceous impression of a complete specimen measuring a little over 10 cm in length. The body is long and slender with a hypocercal tail and a quite large anal fin. There is no evidence of any other fin, nor of any scale in the specimen. Eyes appear to be situated near the top surface of the head. Overall, Cornovichthys looks a lot like Euphanerops and like its Canadian counterpart has a long series of branchial openings running from the head to the anal fin, numbering to around 15 on each side of the body.

Achanarella trewini.

Achanarella trewini is known from many specimens that were found in large numbers on single slabs of rock. Individuals of Achanarella range in size from 2 cm to 9 cm in length. Like Cornovichthys, it has a hypocercal tail and a large anal fin, no apparent scale and a large number of branchial openings on each side of the body, 13 or more, but the body is much thinner and elongated and the head is extremely small. Just like Jamoytius and Euphanerops, Cornovichthys and Achanarella were probably feeding on micro-organisms and detritus through their jawless mouth.

Reference:

Newman, M., & Trewin, N. (2001). A new jawless vertebrate from the Middle Devonian of Scotland. Palaeontology, 44, 43–51.

Newman, M. (2002). A new naked jawless vertebrate from the Middle Devonian of Scotland. Palaeontology, 45(5), 933–941.

The Canadian cousins of Jamoytius

2014-05-04T22:37:00.001-07:00

Euphanerops longaevus

The rich Late Devonian fish fauna of Miguasha, in Eastern Quebec, Canada (Escuminac Formation) includes some peculiar jawless fish closely related to the Silurian scottish species Jamoytius kerwoodi. They have a strongly hypocercal tail with a relatively large anal fin. The body is elongated and have a series of long and narrow weakly mineralized scales on the flanks. The eyes are relatively large and the mouth is a circular opening situated at the bottom of the head. Like most if not all primitive fish, they lack paired fins. The branchial openings were numerous numbering 30 or so (lampreys have only 7 of these gill pouches) aligned from the head to the anal region, and therefore stretching over a very long portion of the body. This peculiar arrangement is thought to be an adaptation to a poorly oxygenated water. The first species to be described is Euphanerops longaevus by the British paleontologist Sir Arthur Smith Woodward in 1900. This strange animal was however originally described upside down, with the anal fin as a dorsal one and an epicercal tail. Euphanerops measured about 10 cm in length. The second species is Endeiolepis aneri described by the swedish paleontologist Erik Stensiö in 1939. It is very similar to Euphanerops and it was suggested that the two represent the same animal, with Euphanerops being the juvenile form. In that case, the name Euphanerops has priority and Endeiolepis would be a junior synonym. Legendrelepis parenti described by M. Arsenault and P. Janvier, 1991 is considered to be a junior synonym as well, any noted differences such as the alleged presence of a dorsal fin are now viewed as artifacts of preservation.

References:

Janvier, P., Desbiens, S., Willett, J. a, & Arsenault, M. (2006). Lamprey-like gills in a gnathostome-related Devonian jawless vertebrate. Nature, 440(7088), 1183–5.

Janvier, P., & Arsenault, M. (2007). The anatomy of Euphanerops longaevus Woodward, 1900, an anaspid-like jawless vertebrate from the Upper Devonian of Miguasha, Quebec, Canada. Geodiversitas, 29(1), 143–216.

The enigmatic jawless fish Jamoytius kerwoodi

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A reconstruction of Jamoytius kerwoodi

The exact affinities of the jawless fish Jamoytius have been at the heart of scientific controversies and heated debate during most of the second part of the 20th century (Ritchie, 1984). The first fossils of this early vertebrate were discovered in 1914 near Lesmahagow, Lanarkshire, central Scotland in beds dating from the Late Silurian period, but awaited more than 20 years before a formal description was published (White, 1946). The species Jamoytius kerwoodi is based on two specimens and was first considered to be a primitive naked fish-like chordate possibly ancestral to the cephalochordate Amphioxus (also called Lancelet). Later studies however reinterpreted the “carbonized muscle remains” described by White as being weakly mineralized scales, similar to those seen in another grade of jawless fish, the Anaspida, and Jamoytius was naturally placed among them. Its branchial apparatus similar to those of a lamprey made it at one point, a possible ancestor of the petromyzontiformes (the group that include the modern lampreys). These branchial openings (gill slits) numbered from 10 to 15 or more and were therefore more numerous than in modern lampreys (seven). The discovery of a few more fossils did little to help settle the debate and details such as the shape and position of the fins remain greatly hypothetical. It appears to have had a dorsal fin, an anal fin and a hypocercal caudal fin although the latter is rather inferred from related species such as Endeiolepis than genuinely observed as preserved in the fossils. The presence of paired fins along the body has never been very conclusive.

It had relatively large eyes and a single nostril. The mouth was circular without teeth. Some authors proposed that Jamoytius represented the larval stage of an ostracoderm or even of a cephalochordate (Wickstead, 1969). This is rather unlikely as the animal has an elongated body of 15 to up to 35 cm, making it one of the largest jawless fish from the Silurian period. The most recent study of this animal (Sansom et al., 2010) using a combination of topological reconstruction, comparative anatomy, elemental mapping and phylogenetic analysis, concluded that Jamoytius and its relatives were definite vertebrates and stem gnathostomes rather than ancestors of lampreys or relatives of the Anaspida.

The absence of teeth indicates that it was either a filter feeder or a detritus feeder. An interesting theory linked to its supposed affinity with lampreys make it a possible suctorial feeder (Ritchie, 1968). In this theory, it is implied that the numerous circular perforations observed in the enigmatic organism Dictyocaris were made by Jamoytius. However there is nothing to back up that claim besides the matching size of the holes with the mouth of Jamoytius. Jamoytius fossils were found alongside numerous remains of another agnathan, Thelodus scoticus, fossils of the problematic taxon Ainiktozoon loganense (most recent study makes it an arthropod), as well as of many arthropods and a few molluscs in what constituted a marine environment. Anyhow, to date, the enigmatic Jamoytius is with Thelodus, still the oldest vertebrate known from the European continent.

References:

Ritchie, A. (1960). A new interpretation of Jamoytius kerwoodi White. Nature, 188(4751), 647–649.

Ritchie, A. (1968). New evidence on Jamoytius kerwoodi White, an important ostracoderm from the Silurian of Lanarkshire, Scotland. Palaeontology, 11(1), 21–39.

Ritchie, a. (1984). Conflicting interpretations of the Silurian agnathan, Jamoytius. Scottish Journal of Geology, 20(2), 249–256.

Sansom, R. S., Freedman, K., Gabbott, S. E., Aldridge, R. J., & Purnell, M. a. (2010). Taphonomy and affinity of an enigmatic Silurian vertebrate, Jamoytius kerwoodi White. Palaeontology, 53(6), 1393–1409.

Wickstead, J. (1969). Some further comments on Jamoytius kerwoodi White. Zoological Journal of the Linnean Society, 48(August), 421–422.

Jawless armored fish from the Ordovician: the Astraspids and Eriptychiids

2014-04-20T18:25:00.001-07:00

My reconstruction of Astraspis desiderata.

The Astraspids and Eriptychiids form other groups of jawless armored fish restricted to the Ordovician. They are the earliest known definite vertebrates from North America. Like the Arandaspids, they apparently all went extinct at the end of the period. Unlike the Arandaspids, their head shield carapace is made of hundreds of very small and separate bony pieces called tesserae. They have polygonal shape surmounted by tubercles of various morphologies. Their ornamentation and shape are different depending on their position in the carapace, so that a tesserae from the dorsal plate can be distinguished from one from the ventral plate. Two genera are known, Astraspis and Eriptychius, both originally described from the same location, the Late Ordovician (~ 455 MYA) Harding Sandstone, near Cañon City in Colorado, United States, and in the same 1892 paper authored by Charles D. Walcott, the discoverer of the famous Burgess Shale. It is still unclear how these two genera are related and they were often placed in two separate families, Astraspidae and Eriptychiidae or even orders, Astraspida and Eriptychiida. The microstructure of Eriptychius’s tesserae placed them closer to the Heterostraci than Astraspis.

Astraspis desiderata is the better known species with at least three mostly complete and articulated specimens. It had 8 branchial openings on its sides with well developed eyes in the front. The tail is made of large rhomboid scales. Astraspis desiderata measured about 20 cm in length. A seemingly larger species, Pycnaspis splendens has been described in 1958 by Swedish paleontologist Tor Ørvig from the Harding Sandstone of Bighorn Mountains in Wyoming, United States but this one is now considered to be synonymous with Astraspis desiderata. Isolated tesserae attributed to Astraspis have been found throughout North America, in Colorado, Wyoming, South Dakota, Ontario, Quebec and Oklahoma

Eriptychius americanus was only known from isolated and highly ornamented tesserae. The situation changed dramatically in 1967 with the discovery of an articulated specimen consisting of the front part of the dorsal shield (Denison, 1967). A second species, Eriptychius orvigi, honoring Ørvig and from the Bighorn Mountains of Wyoming, with seemingly thicker tesserae, was erected in the same paper, but is now considered to be synonymous with E. americanus.

Just like the Arandaspids, the Astraspids and Eriptychiids did not have any paired fins and would have been rather poor swimmers. They were probably living at the bottom of the sea floor in a sublittoral environment.

References:

Sansom, I. J., Smith, M. P., Smith, M. M., & Turner, P. (1997). Astraspis-the anatomy and histology of an Ordovician fish. Palaeontology, 40(3), 625–643.

Elliott, D. K. (1987). A Reassessment of Astraspis desiderata, the Oldest North American Vertebrate. Science (New York, N.Y.), 237(4811), 190–2.

Bryant, W. (1936). A study of the oldest known vertebrates, Astraspis and Eriptychius. Proceedings of the American Philosophical Society, 76(4), 409–427.

Denison, R. (1967). Ordovician vertebrates from western United States. Fieldiana: Geology, 16(6), 131–192.

Jawless armored fish from the Ordovician: the Arandaspids

2014-04-13T18:56:00.000-07:00

Jawless armored fish from the Ordovician: the Arandaspids

My reconstruction of Sacabambaspis janvieri.

The fossil record of fish during the Ordovician, the period that follows the Cambrian around 485 MYA, is quite poor and consists of just a little more than a handful of named taxa. One of the prominent groups of that time appears to be the Arandaspids. They were jawless (a condition shared by all other vertebrates in these ancient seas) and characterized by a head covered with a bony shield consisting of a flattish dorsal plate, a rounded ventral plate, and a few other smaller plates. Arandaspids were quite primitive looking with two eyes and two nostrils in the front, a series of branchial openings, each protected by bony platelets, on the side between the dorsal and ventral plates. The back portion of the animal was protected by strips of bony armor arranged in chevrons. They had a caudal fin, but no paired fin, making them not particularly good swimmers. They probably lived on the seafloor feeding on microorganisms or organic detritus sucked in through their jawless mouth. All Arandaspids were marine.

My reconstruction of Arandaspis prionotolepis.

The type species of the group is Arandaspis prionotolepis from the shallow marine deposits of the Stairway Sandstone in the Northern Territory, Australia, and dating from the Earliest Middle Ordovician. This 10-15 cm long fish, originally described in 1977 (Ritchie & Gilbert-Tomlinson, 1977) is known from several specimens, some quite complete. The other relatively well known species is Sacabambaspis janvieri from the Anazaldo Formation of Bolivia, which was discovered among a fauna composed almost exclusively of lingulid brachiopods, an indication that it lived near the littoral in a well oxygenated area. Initially described from three bone fragments in 1986 (Gagnier & Blieck, 1986), new fossils were later found including a complete articulated specimen (Pradel et al., 2007) that preserved the uniquely shaped hypocercal tail (the end tip of the vertebral column bends downward supporting the bottom lobe of the tail). The Anzaldo Formation was originally believed to be of Early Upper Ordovician age, but it may actually have been older making Sacabambaspis quite contemporary with Arandaspis (Gagnier et al., 1996). Sacabambaspis was a bit larger than its Australian counterpart, reaching a length of 25 cm.

Articulated fossil specimen of Sacabambaspis janvieri. From User:Ghedoghedo, Wikipedia commons

Another fish, Andinaspis suarezorum from the Capinota Formation of Bolivia, known from a single poorly preserved fragment, was once thought to be Early Middle Ordovician and classified as a possible Arandaspid, but there are now doubts on its actual age, which turned out to be in all probability Devonian (Gagnier et al., 1996). Also from Bolivia, but from the Pircancha Formation of Early Ordovician age, comes what seems to a be ventral shield of a possible large Arandaspid christened Pircanchaspis rinconensis (Erdtmann et al., 2000) This is the earliest record of a fish from South America. From Australia, Porophoraspis crenulata from the same location and age than Arandaspis was described in the same paper than the latter, but is much less known as only a single external mould of a small plate has been recovered. This one is also a possible Arandaspid.

Arandaspids belong to one of the two major groups of armored jawless fish that would dominate the first part of the Paleozoic era: the Heterostraci or Heterostracomorphs, the other group being the Cephalaspids. Arandaspids apparently did not last longer than the Ordovician, being replaced by far more efficient forms in the Silurian.

References:

Erdtmann, B., Weber, B., Schultze, H.-P., & Egenhoff, S. (2000). A possible agnathan plate from the Lower Arenig (Lower Ordovician) of South Bolivia. Journal of Vertebrate Paleontology, 20(2), 394–399.

Gagnier, P., Blieck, A., & G., R. S. (1986). First Ordovician vertebrate from South America. Geobios, 19(5), 629–634.

Gagnier, P., Blieck, A., Emig, C., Sempere, T., Vachard, D., & Vanguestaine, M. (1996). New paleontological and geological data on the Ordovician and Silurian of Bolivia. Journal of South American Earth Sciences, 9(5/6), 329–347.

Pradel, A., Sansom, I. J., Gagnier, P.-Y., Cespedes, R., & Janvier, P. (2007). The tail of the Ordovician fish Sacabambaspis. Biology Letters, 3(1), 73–76.

Ritchie, A., & Gilbert-Tomlinson, J. (1977). First Ordovician vertebrates from the southern hemisphere. Alcheringa, 1(4), 351–368.

Early vertebrates: the Myllokunmingiidae

2014-04-06T18:57:00.000-07:00

My reconstruction of the early vertebrate Haikouichthys ercaicunensis, based on Zhang & Hou, 2004.

Early vertebrates: the Myllokunmingiidae

Molecular data of extant fauna places the divergence of vertebrates (animals with a backbone, including mammals, birds, reptiles, amphibians and fish) from their closest relatives, the cephalochordates (Amphioxus) as far back as 751 MYA (Hedges, 2001) during the Cryogenian period of the proterozoic. This is well before the Ediacaran biota (575 MYA) and the so-called Cambrian explosion (542 MYA). However, it was recently shown that the molecular clock ran some five times faster during the Cambrian than during any other period that followed (Lee, 2013). A more conservative and reasonable estimate would therefore make the vertebrates appeared at the very end of the Proterozoic or during the Lower Cambrian along many other phyla. What does the fossil record says? For a while, the earliest undisputed vertebrate fossil remains consisted of some isolated dermal bones dating from the Early Ordovician (480 MYA) of central Australia and belonging to a group of jawless fish called Arandaspida. This situation changed quite a bit in 1999 with the discovery and description of two fossils from the famous Chengjiang biota of the Maotianshan Shale in the Yunnan Province of China, dating from the middle of the Lower Cambrian (525-520 MYA). Two species were erected, Myllokunmingia fengjiaoa Shu et al., 1999 and Haikouichthys ercaicunensis Luo et al., 1999, regrouped into the family Myllokunmingiidae. A third species, Zhongjianichthys rostratus Shu, 2003 has been added to the list four years later.

Haikouichthys (“Haikou fish”) is by far the best known of the three. Originally based on a single incomplete specimen, it is today known from more than 500 specimens from the same fossil locality near Haikou, in the Kunming prefecture of Yunnan. Measuring about 2.5 cm in length, Haikouichthys has an elongated fish-like body with a single dorsal, ventral and caudal fin, as shown from a remarkably well-preserved specimen (Zhang & Hou, 2004). It is not easy to interpret faint impressions within the fossils but structures and internal organs such as vertebrae, paired eyes, guts, heart, and possibly a nostril, an olfactory organ have been identified. Haikouichthys had a number of gill pouches and series of W shape myomeres (muscle blocks that are typical in fish). The presence of a mouth can only be inferred as it is not clearly visible in the fossils. Haikouichthys was certainly an active swimmer but probably not a good one because of the lack of paired fins. Haikouichthys and the other Myllokunmingiids appear to be the most primitive agnathans (jawless fish). Phylogenetic analysis indicates that this is a stem vertebrate more primitive than lampreys and any other known jawless fish.

Myllokunmingia (“Kunming fish”) is known from a single 2.8 cm long specimen. It is usually seen as being a bit larger and bulkier than Haikouichthys. However, a new fossil (Hou et al., 2002) showing a combination of characters found in Haikouichthys and Myllokunmingia, may indicate that the two constitute in fact a single animal (in that case, the name Myllokunmingia would have precedence over Haikouichthys) and any observed differences may rather reflect preservation bias. This view is however not universally recognized. Zhongjianichthys is a problematic animal that has been classified as a Myllokunmingiid, but not enough is known about it for this attribution to be certain. Another Maotianshan Shale animal, Haikouella lanceolata Chen, Huang & Li, 1999, known from more than 300 specimens, is often considered as another possible stem vertebrate. However it looks so similar to the contemporaneous Yunnanozoon lividum, a possible hemichordate or stem chordate, that this attribution is somewhat unlikely. Most specimen of Haikouella measured 2.5 to 3 cm in length with some individuals reaching 4 cm.

Reference:

Chen, J., Huang, D., & Li, C. (1999). An early Cambrian craniate-like chordate. Nature, 402(December), 518–522.

Hedges, S. (2001). Molecular evidence for the early history of living vertebrates. In Major Events in Early Vertebrate Evolution, 119–134.

Lee, M. S. Y., Soubrier, J., & Edgecombe, G. D. (2013). Rates of phenotypic and genomic evolution during the Cambrian explosion. Current Biology, 23(19), 1889–95.

Shu, D., Luo, H., Morris, S., Zhang, X., & Hu, S. (1999). Lower Cambrian vertebrates from south China. Nature, 402(November), 42–46.

Shu, D., Morris, S., Han, J., & Zhang, Z. (2003). Head and backbone of the Early Cambrian vertebrate Haikouichthys. Nature, 421(January), 526–529.

Xian-guang, H., Aldridge, R. J., Siveter, D. J., Siveter, D. J., & Xiang-hong, F. (2002). New evidence on the anatomy and phylogeny of the earliest vertebrates. Proceedings. Biological Sciences / The Royal Society, 269(1503), 1865–9.

Zhang, X.-G., & Hou, X.-G. (2004). Evidence for a single median fin-fold and tail in the Lower Cambrian vertebrate, Haikouichthys ercaicunensis. Journal of Evolutionary Biology, 17(5), 1162–6.

Old views on dull-witted semi-aquatic dinosaurs correct after all…

2014-04-01T09:13:00.005-07:00

A new study suggests dinosaurs were aquatic... too heavy to move on land.

For more than half a century, dinosaurs were depicted as slow-moving creatures living in swampy environments. Giants such as the 35 tons Brachiosaurus were deemed too heavy on land to be able to support their own weight and the prominent view for most of the 20th century was that they were amphibious animals that spent most of their time half-submerged in water, grazing on soft aquatic plants. Dinosaurs were also thought to be incredibly stupid in view of their very small braincase. For instance, the plated Stegosaurus had a brain the size of a walnut which is indeed minuscule for an animal reaching 9 m in length. This view on dinosaurs drastically changed starting in the 1960s (the so-called “dinosaur renaissance”) when new discoveries such as the numerous fossils of the duck-billed dinosaur Maiasaura found at “Egg Mountain” in Montana, and encompassing individuals of all ages from hatchlings to adults, purportedly showed that dinosaurs raised their youngs and thus had intelligence matching those of modern mammals and birds. Today, dinosaurs are ubiquitously portrayed as highly active fully terrestrial creatures capable of a wide range of social behavior such as pack hunting and parental care.

The old view of dinosaurs as dull-witted amphibious beasts has been totally abandoned and these animals are now often seen as one of the prime evolutionary successes rather than as a failed nature experiment doomed for extinction. However, in recent years, scattered discoveries indicated that at least some dinosaurs were aquatic: in the 1970s, a new specimen of the little theropod Compsognathus found in southern France was described as having webbed feet indicative of a semi-aquatic lifestyle. In 2010, the analysis of the oxygen isotope ratios in Spinosaurus teeth showed that it was close to those of crocodiles and aquatic turtles, proving that the giant sailed theropod spent lots of time in water. In 2011, a new ceratopsian dinosaur, Koreaceratops, was described as having a tail adapted for swimming. Now, a new study published in the April 2014 issue of the Journal of the Australian Society of Vertebrate Palaeontology, shows that the aquatic lifestyle of dinosaurs was actually widespread. The study applied the same isotopic analysis technique used for Spinosaurus, on the teeth of some 20 species of sauropods (the long-necked, long-tailed giants such as Diplodocus and Brachiosaurus) and ornithopods (including the duck-billed dinosaurs such as Parasaurolophus and Edmontosaurus) from the Late Jurassic and Late Cretaceous of North America. The results show for all teeth a level of oxygen isotopes compatible with life in water. “This technique has until now only been applied to Spinosaurus because a fish-eating diet was long suspected for this theropod due to its crocodile-like snout. Nobody thought to check on dinosaurs such as Brachiosaurus or Edmontosaurus as the general consensus was that these were fully terrestrial” says lead author Dr. Avril Zierste from the Palaeontology department of the University of Sao Paulo. “The results came quite as a shock because the current views on these ancient creatures will have to take a 180 degree turn”, she adds. Many observed dinosaurian features that were left unexplained as land animals, make perfect sense if they were water dwelling gentle giants. For instance, the flattened tail of duck-billed dinosaurs rigidified by ossified tendons, were superbly adapted for swimming. Moreover the often complex nasal apparatus of many of these same duck-billed dinosaurs were probably used as snorkels to breathe while underwater, as initially hypothesized well before the “dinosaur renaissance". Sauropod bones are well known to show high degree of pneumaticity, which are seen as evidence of the presence of air sacs. This purpose of this becomes clear if these animals were aquatic as air sacs will help with buoyancy and act as floating devices. It is probably not a coincidence that fossils of dinosaurs around the world were predominantly found in regions that were very close to water and often among remains of marine or freshwater animals such as fish and crocodiles.

Old depiction of Brachiosaurus depicted as aquatic animals by Czech painter Z. Burian (1905-1981). New study suggests early paleontologists were right from the beginning about the lifestyle of dinosaurs.

Is it possible that the current view of terrestrial dinosaurs with high metabolism portrayed after the “dinosaur renaissance” was more based on wishful thinking than hard evidences? The eminent scholar Josh Mothorn certainly thinks so: “We were so keen to believe that no group of animals could have dominated the earth for 165 millions years without sharing at least some of the qualities of our kind, the mammals, such as warm-bloodedness and intelligence, that any circumstances tending to indicate that they were something else than slow moving idiotic monsters, were branded as evidence of complex behavioral habit. The fact is that movies such as “Jurassic Park” would never have been successful if the heroes were confronted not by incredibly fast and skillful killing machines but by clumsy sluggish creatures that could be easily fooled and outsmarted”. “The dinosaur renaissance is dead” concludes Art Kerbebrok after hearing the conclusions of the study “it is high time that we stop imagining them as nothing more than stupid giants too heavy to support their own weight. People were quick to dismiss the obvious: their brain to body size ratios were among the smallest in any tetrapods. Dinosaurs were slow, gigantic and idiotic. Mammals have outwitted them, that’s why dinosaurs are extinct”. In light of the new study by Dr. Zierste and co-workers, it seems that the old prevalent view of dinosaur as slow-witted and placid semi-aquatic giants was correct after all.

Reference:

Avril Z., Peter S. G., Robert T. B., Ines L. P., Lambert J. B., Stewart M.T., Fernando E. N., Oviedo T. F., Oscar J., Lewis C. C. (April 1, 2014) “Oxygen isotope analysis and brain-body ratio measurements of 20 species of Sauropoda and Ornithopoda as evidence for semi-aquatic lifestyle and low I.Q. for the clade Dinosauria” J. of Australian Society of Vertebrate Palaeontology, 90., 1-12.

A unique feeding specialization in a prehistoric porpoise

2014-03-16T12:50:00.001-07:00

Life reconstruction of a pair of Semirostrum ceruttii

Porpoises (Family Phocoenidae) are among the smallest cetaceans (whales). They live in coastal regions, feeding on fish and squids on the sea floor. The six living species of porpoises are distributed in all the oceans of the world. Porpoises are a quite recent addition to the cetacean world, having diverged from the dolphins probably during the middle of the Miocene period. Fossil porpoises are all very similar to their modern counterparts and do not show much specialization, with the exception of the newly discovered Semirostrum ceruttii from the Pliocene San Diego and Purisima formations of California.

The Black Skimmer (Rynchops niger) (photo by Dan Pancano)

Semirostrum is unique among the cetaceans for its nearly toothless lower jaw that is some 40% longer than its upper jaw. The many mandibular canals found in this protruding lower jaw indicate that this was a richly innerved and vascularized area and was most probably used for prey detection. The slightest touch would provoke the immediate closure of the mouth. A modern equivalent of such apparatus is given by the beak of the skimmer (Rhynchops), a tern-like seabird that hunts by flying close to the water surface, skimming the waves with its lower jaw. Semirostrum would have done the same at the bottom of the seafloor in search of small preys living close to the sand surface. This high degree of feeding specialization (called skim-feeding) is rather unprecedented among mammals. Semirostrum lived alongside other benthic foraging mammals such as the near toothless walrus Valenictus and the baleen whale Herpetocetus, indicating an unique shallow water ecosystem. Semirostrum is known from an almost complete skull and several referred specimens that include postcranial elements.

Semirostrum scale diagram

Ref: Rachel A. Racicot, Thomas A. Deméré, Brian L. Beatty & Robert W. Boessenecker. 2014. Unique Feeding Morphology in a New Prognathous Extinct Porpoise from the Pliocene of California. Current Biology. Published online.

One crazy Sauropterygian

2014-02-02T20:12:00.001-08:00

You won’t believe what crazy prehistoric critter has just been described from the Middle Triassic (Anisian) Luoping fauna of the Yunnan province of China. The site is world famous for his rich collection of well-preserved fossils of shallow sea marine reptiles that include primitive ichthyosaurs, protorosaurs and pachypleurosaurs.

Atopodentatus unicus is a Sauropterygian with a typical body plan of a primitive Sauropterygian, elongated, with a long tail, and paddle-like limbs. However the neck is fairly short and the head minuscule. But what a head! It is from the sort that only a mother could love. The tip of the snout is bent downward and the jaw is filled with numerous needle like teeth. The most bizarre aspect of the snout is that its front is split in two and armed with more teeth forming a kind of non-functional second jaw. This bizarre apparatus has been linked to a very specialized diet. The animal was probably shoveling sand at the bottom of the sea to trap small crustaceans and worms inside the cage made by its delicate teeth.

If you don’t have access to the full paper in Naturwissenshaften, go check Jaime Headden’s blog for a vivid description of the remains of this peculiar critter.

Here is the abstract of the paper:

Abstract

The Luoping fauna (Anisian, Middle Triassic) is probably the oldest of Triassic faunas in Guizhou–Yunnan area, China. The reptilian assemblage is comprised of ichthyosaurs, a number of sauropterygians (pachypleurosaur-like forms), saurosphargids, protorosaurs, and archosauriforms. Here, we report on a peculiar reptile, newly found in this fauna. Its dentition is fence or comb-like and bears more than 175 pleurodont teeth in each ramus of the upper and lower jaws, tooth crown is needle-like distally and blade-shaped proximally; its rostrum strongly bends downward and the anterior end of its mandible expands both dorsally and ventrally to form a shovel-headed structure; and its ungual phalanges are hoof-shaped. The specializations of the jaws and dentition indicate that the reptile may have been adapted to a way of bottom-filter feeding in water. It is obvious that such delicate teeth are not strong enough to catch prey, but were probably used as a barrier to filter microorganisms or benthic invertebrates such as sea worms. These were collected by the specialized jaws, which may have functioned as a shovel or pushdozer (the mandible) and a grasper or scratcher (the rostrum). Our preliminary analysis suggests that the new reptile might be more closely related to the Sauropterygia than to other marine reptiles.

Reference: Cheng, L.; Chen, X.-H.; Shang, Q.-H. and Wu X.C. 2014. A new marine reptile from the Triassic of China, with a highly specialized feeding adaptation. Naturwissenschaften. In press.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com)

2013 in Paleontology

2014-01-01T11:23:00.001-08:00

A selection of species described in 2013

Here is my pick for the top paleontology stories of year 2013 (not in particular order):

Archicebus achilles

1) The discovery in the Hubei province of China of the oldest haplorhine primate skeleton, Archicebus achilles., dating from the Eocene.

Reference: Ni, X.; Gebo, D. L.; Dagosto, M.; Meng, J.; Tafforeau, P.; Flynn, J. J.; Beard, K. C. 2013. The oldest known primate skeleton and early haplorhine evolution. Nature 498 (7452): 60–64.

Entelognathus primordialis

2)Entelognathus primordialis, a Placoderm fish with a modern type jaw that rewrites the history of jaw evolution in vertebrates.

Reference: Zhu, Min; Xiaobo Yu, Per Erik Ahlberg, Brian Choo, Jing Lu, Tuo Qiao, Qingming Qu, Wenjin Zhao, Liantao Jia, Henning Blom & You'an Zhu 2013. A Silurian placoderm with osteichthyan-like marginal jaw bones. Nature (502): 188–193.

3) A new study using computer mechanical simulation coupled with high resolution CT scans has indicated that theropod dinosaur beaks evolved to stabilize the skull during biting and feeding rather than as a lightweight replacement for teeth as previously assumed.

Microraptor gui

Reference: Lautenschlager, Stephan et al. 2013. Edentulism, beaks, and biomechanical innovations in the evolution of theropod dinosaurs. PNAS. in press.

4) Microraptor gets a highlight again with the description of a specimen with fish scales in its abdominal cavity proving that it was an opportunistic feeder that also was also piscivorous.

Reference: Lida Xing et al. 2013. Piscivory in the feathered dinosaur Microraptor. Evolution. 67(8): 2441–2445.

Tsintaosaurus spinorhinus

5) Two familiar duck-billed dinosaurs got facelifts with the redescription of the crest of Tsintaosaurus and the finding of a soft tissue wattle on the head of one well preserved specimen of Edmontosaurus.

Reference: Prieto-Márquez, A.; Wagner J.R. 2013. The ‘Unicorn’ Dinosaur That Wasn’t: A New Reconstruction of the Crest of Tsintaosaurus and the Early Evolution of the Lambeosaurine Crest and Rostrum.. PLoS ONE 8 (11): e82268.

Bell, P. R.; Fanti, F.; Currie, P. J.; Arbour, V. M. 2013. A Mummified Duck-Billed Dinosaur with a Soft-Tissue Cock's Comb. Current Biology. in press.

Edmontosaurus regalis

6) A new methodology has clocked the rate of evolution of arthropods and it was found to be four to five times faster during the so-called "Cambrian explosion" than after it.

Reference: Michael S.Y. Lee, Julien Soubrier, Gregory D. Edgecombe, Rates of Phenotypic and Genomic Evolution during the Cambrian Explosion, Current Biology, Volume 23, Issue 19, 7 October 2013, Pages 1889-1895.

Lythronax argestes

7) At 8 meters in length, the tyrannosaurid Lythronax argestes from the Cretaceous of Utah emerges as the new rising star among the dinosaur enthusiasts and t-rex lovers.

Reference: Loewen, M. A.; Irmis, R. B.; Sertich, J. J. W.; Currie, P. J.; Sampson, S. D. 2013. Tyrant Dinosaur Evolution Tracks the Rise and Fall of Late Cretaceous Oceans. In Evans, David C. PLoS ONE 8 (11): e79420.

8) Three new ceratopsians from North America have been described: Bravoceratops from Texas, Nasutoceratops from Utah and Judiceratops from Montana.

Judiceratops tigris

Reference: Longrich, N. R. 2013. Judiceratops tigris, a New Horned Dinosaur from the Middle Campanian Judith River Formation of Montana. Bulletin of the Peabody Museum of Natural History 54: 51–65.

Sampson, S. D.; Lund, E. K.; Loewen, M. A.; Farke, A. A.; Clayton, K. E. 2013. A remarkable short-snouted horned dinosaur from the Late Cretaceous (late Campanian) of southern Laramidia. Proceedings of the Royal Society B: Biological Sciences 280 (1766): 2013118.

Wick, S. L.; Lehman, T. M. 2013. A new ceratopsian dinosaur from the Javelina Formation (Maastrichtian) of West Texas and implications for chasmosaurine phylogeny". Naturwissenschaften. in press (7): 667.

Panthera blytheae

9) Panthera blytheae from the Late Miocene of Tibet is the oldest known big cat (genus Panthera) that includes lions, tigers, panthers, leopards and jaguars, and points to an asian origin for them.

Reference: Tseng, Jack; Wang, Xiaoming; Slater, Graham J. ; Takeuchi, Gary T. ; Li, Qiang; Liu, Juan; and Xie, Guangpu. 2014. Himalayan fossils of the oldest known pantherine establish ancient origin of big cats. Proceedings of the Royal Society B 281 (1774): 20132686.

10) Rock legend Jim Morrison has now a prehistoric animal named after him, the 2 meter long iguana relative, Barbaturex morrisoni.

Barbaturex morrisoni

Reference: Head, J. J.; Gunnell, G. F.; Holroyd, P. A.; Hutchison, J. H.; Ciochon, R. L. 2013. Giant lizards occupied herbivorous mammalian ecospace during the Paleogene greenhouse in Southeast Asia. Proceedings of the Royal Society B: Biological Sciences 280 (1763): 20130665.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com)

Ajancingenia yanshini

2013-11-19T23:03:00.000-08:00

After more than 30 years, the oviraptorid "Ingenia" yanshini finally got a new name: officially, it is now Ajancingenia yanshini. This dinosaur, first described in 1981 by Rinchen Barsbold from a fragmentary skeleton, was originally christened "Ingenia" but this generic name turns out to be preoccupied by a nematode worm therefore necessitating a new denomination. The paper announcing the change of name was published in Zootaxa by one Jesse Easter and all sounded very well until I saw THIS! Shame on you, Mr Easter, this is not cool... not cool at all.

Ref:

R. Barsbold. 1981. Bezzubyye khishchnyye dinozavry Mongolii [Toothless carnivorous dinosaurs of Mongolia]. Sovmestnaia Sovetsko-Mongol’skaia Paleontologicheskaia Ekspeditsiia Trudy 15:28-39

J. Easter. 2013. A new name for the oviraptorid dinosaur "Ingenia" yanshini (Barsbold, 1981; preoccupied by Gerlach, 1957). Zootaxa. 3737(2), 184-190.

M. Mortimer. Theropod Database information on "Ingenia" published! ... by someone else

A. Cau. Il preoccupante caso del preoccupato Ingenia [AGGIORNAMENTO]

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com). Check out my portfolio at spinops.blogspot.com.

Deinocheirus the magnificent

2013-11-03T22:20:00.001-08:00

A tentative recon of Deinocheirus while awaiting the official publication describing two new skeletons

Apparently, the mysterious Deinocheirus was more freaking awesome than you could ever have imagined... as recently revealed at SVP 2013! Here is the abstract:

New Specimens of Deinocheirus mirificus from the Late Cretaceous of Mongolia

Lee, Yuong-Nam; Barsbold, Rinchen; Currie, Philip; Kobayashi, Yoshitsugu & Lee, Hang-Jae.

Abstract: The holotype of Deinocheirus mirificus was collected by the Polish-Mongolian Palaeontological Expedition at Altan Uul III in 1965. Because the holotype was known mainly on the basis of giant forelimbs with scapulocoracoids, Deinocheirus has remained one of the most mysterious dinosaurs. Two new specimens of Deinocheirus were discovered in the Nemegt Formation of Altan Uul IV in 2006 and Bugin Tsav in 2009 by members of the Korea-Mongolia International Dinosaur Expedition (KID). Except for the skull, middle dorsal and most of the distal caudal vertebrae, the right forelimb, left manus, and both pedes, the remaining parts of the skeleton (Mongolian Paleontological Center [MPC]-D 100/127) including a left forelimb clearly identifiable as Deinocheirus were collected. The humerus (993 mm in length) is longer than the 938 mm humerus of the holotype. The Altan Uul IV specimen (MPC-D 100/128) is a subadult Deinocheirus (approximately 72% of MPC-D 100/127), which consists of post-cervical vertebrae, ilia,ischia, and hind limbs. Both specimens provide important paleontological evidence for exact postcranial reconstruction of Deinocheirus mirificus. Cladistic analysis indicates that Deinocheirus is a basal member of Ornithomimosauria, but many new unique skeletal features appear to be quite different from other ornithomimosaurs. These include extreme pneumaticity of tall, anterodorsally oriented distal dorsal neural spines (7~8times taller than centrum height) with basal webbing, fused sacral neural spines forming a midline plate of bone that extends dorsally up to 170% of the height of the ilium, ventrally keeled sacral centra, a well-developed iliotibialis flange, a posterodorsally projecting posterior iliac blade with a concave dorsal margin, a steeply raised anteriordorsal margin of the ilium, an anteriorly inclined brevis shelf, vertically well-separatediliac blades above the sacrum, an completely enclosed pubic obturator foramen, triangular pubic boot in distal view, vertical ridges on anterior and posterior edges of medial surface of the femoral head, and a robust femur that is longer than tibiotarsus. These features suggest that Deinocheirus (unlike other ornithomimosaurs) was not a fast running animal, but a bulky animal with a heavily built pelvis and hind limbs. However,the dorsal ribs are tall and relatively straight, suggesting that the animal was narrow-bodied. A large number of gastroliths (>1100 ranging from 8 to 87 mm) were collected from the abdominal region of MPC-D 100/127, suggesting Deinocheirus was an herbivore.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com). Check out my portfolio at spinops.blogspot.com.

New Multituberculate fossil shows keys to their success

2013-08-17T21:27:00.000-07:00

Reconstruction of Rugosodon eurasiaticus.

Multituberculates are a highly successful group of early mammals and they were surprisingly long lived having evolved in the Jurassic, survived the KT extinction event before disappearing during the Oligocene period. They are in fact the most long-lasting group of mammals, having survived at least 130 million years, more than any other group of mammals either alive or extinct. A new mostly complete fossil discovered in China, Rugosodon eurasiaticus, greatly help clarify the origin of the group. It shows that some of the key characteristics of the multituberculates, such as highly flexible spine and mobile ankle joints, evolved very early, and were probable the reasons of their success.

Reference:

Ref: Yuan C.-X., Ji Q., Meng Q.-J., Tabrum A. R., Luo Z.-X. 2013. Earliest evolution of multituberculate mammals revealed by a new Jurassic fossil. Science 341 (6147): 779–783.

Abstract: Multituberculates were successful herbivorous mammals and were more diverse and numerically abundant than any other mammal groups in Mesozoic ecosystems. The clade also developed diverse locomotor adaptations in the Cretaceous and Paleogene. We report a new fossil skeleton from the Late Jurassic of China that belongs to the basalmost multituberculate family. Dental features of this new Jurassic multituberculate show omnivorous adaptation, and its well-preserved skeleton sheds light on ancestral skeletal features of all multituberculates, especially the highly mobile joints of the ankle, crucial for later evolutionary success of multituberculates in the Cretaceous and Paleogene.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com). Check out my portfolio at spinops.blogspot.com.

And then there were nine...

2013-08-15T23:00:00.001-07:00


The top right species is now synonymous with the top left one.

Up to 15 species of Psittacosaurus have been described in the scientific litterature, but a few are dubious and others have been shown to be synonymous. With the latest 3D geometric morphometric study of the skulls of the three species of Psittacosaurids from the Lujiatun beds of the Yixian Formation of China, this number is now down to nine: Hongshanosaurus houi and Psittacosaurus major are now taxonomically dead...

Psittacosaurus lujiatunensis

Here is the paper and abstract:
Hedrick BP, Dodson P (2013) Lujiatun Psittacosaurids: Understanding Individual and Taphonomic Variation Using 3D Geometric Morphometrics. PLoS ONE 8(8): e69265.

Abstract:

Psittacosaurus is one of the most abundant and speciose genera in the Dinosauria, with fifteen named species. The genus is geographically and temporally widespread with large sample sizes of several of the nominal species allowing detailed analysis of intra- and interspecific variation. We present a reanalysis of three separate, coeval species within the Psittacosauridae; P. lujiatunensis, P. major, and Hongshanosaurus houi from the Lujiatun beds of the Yixian Formation, northeastern China, using three-dimensional geometric morphometrics on a sample set of thirty skulls in combination with a reevaluation of the proposed character states for each species. Using these complementary methods, we show that individual and taphonomic variation are the joint causes of a large range of variation among the skulls when they are plotted in a morphospace. Our results demonstrate that there is only one species of Psittacosaurus within the Lujiatun beds and that the three nominal species represent different taphomorphotypes of P. lujiatunensis. The wide range of geometric morphometric variation in a single species of Psittacosaurus implies that the range of variation found in other dinosaurian groups may also be related to taphonomic distortion rather than interspecific variation. As the morphospace is driven primarily by variation resulting from taphonomic distortion, this study demonstrates that the geometric morphometric approach can only be used with great caution to delineate interspecific variation in Psittacosaurus and likely other dinosaur groups without a complementary evaluation of character states. This study presents the first application of 3D geometric morphometrics to the dinosaurian morphospace and the first attempt to quantify taphonomic variation in dinosaur skulls.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com). Check out my portfolio at spinops.blogspot.com.

The Late Permian Diapsids, Part I

2013-07-27T12:11:00.001-07:00

The Late Permian Diapsids, Part I

In a previous post, I have covered the emergence of the diapsids during the Late Carboniferous and Early Permian. We don't really know what happened next as the diapsidian fossil record is unfortunately very sketchy between the Kungurian when we left Araeoscelis gracilis and the very end of the Late Permian period when diapsids reappear as fossils in reasonable number at a handful of locations on the planet.

Fig. 1.- Reconstructed skull of Lanthanolania ivakhnenko (after Modesto et al., 2003).

Through the entire Middle Permian, the diapsids constitute what scientists call a 'ghost lineage': we merely know they were there because their existence is attested before and after that time but no fossil has been found dating from that period. Well, almost... there is one single partial skull discovered in the Mezen River basin in the Arkhangel'sk province of Russia which was named Lanthanolania ivakhnenko (Modesto et al, 2003). This was a small neodiapsid, probably no more than 30 cm long judging from the 3 cm small skull. The fossil is the only diapsid found among hundreds of other amniote specimens in the Mezen river basin and was naturally overlooked, originally labeled as yet another specimen of the synapsid Mesenosaurus (the generic name Lanthanolania means 'forgotten ripper'). Diapsids were obviously a rare thing at that time, living in the shadows of the larger and more successful synapsids, anapsids and enormous amphibians. The specimen dates from the Uppermost Kazanian or the lowermost Tatarian around 260 MYA which translates into anything between the ICS Wordian (~265 MYA) and the ICS Wuchiapingian (~257 MYA) stages. Although the discovery of Lanthanolania created a little sensation among the specialists in filling the gap, it did not say much on the evolution of the group partly due to the quite fragmentary nature of the finds. All we know is that between the Early Permian and the Late Permian, the Araeoscelids were gone forever and that the terrestrial Neodiapsids survived and somehow diversified.

Fig 2.- Reconstruction of Youngina capensis.

In the Late Permian, a motley crew of forms collectively and formerly called "Eosuchians" (which means “early crocs”) was present. The Eosuchians do not constitute a natural group and their classification and phylogenetic relations are a bit hazy. At first it appeared that the Eosuchians should be divided into the ancestors of the lepidosaurians (lizards, snakes and such) and the ancestors of the archosaurs (crocs, dinosaurs, etc...) but current understanding is that the story is more complicated than this. The most recent cladogram (Reisz et al., 2011) shows a seemingly paraphyletic "younginiformes" group as the most basal eosuchians, with both terrestrial and aquatic forms, then the aquatic form Claudiosaurus (once thought to be a basal Sauropterygian), followed by some members of a family of terrestrial forms called "paliguanids", and finally the gliding coelurosauravids. None of them left any descendants and disappeared in the Early Triassic. Accompanying these "Eosuchians" in the Late Permian were the first members of the Archosauromorphs: the semi-aquatic protorosaurids.

Fig 3.- Skull of Youngina capensis.

Let's first go over the so-called "younginiformes", starting with the terrestrial ones. Youngina capensis was a small lizard-like creature that was first described from a partial skull (Broom, 1914) found in the Dicynodon assemblage zone of South Africa and dating from the latest Permian period. Youngina lived alongside a rich fauna of synapsids, including dicynodonts, gorgonopsids and biarmosuchians and anapsid reptiles, in what was a semi-arid environment. Since its original description, several fossils of Youngina, mostly skulls, were found, receiving different names (Youngoides, Youngopsis, etc...) that are all now considered to be synonymous to Youngina. One peculiar characteristics of Youngina is its single row of osteoderms on its back. A remarkable discovery consists of a set of 5 juvenile, fully articulated and complete individuals, indicating that those critters most certainly lived in a den (Smith &Evans, 1996).

The next two taxa are only tentatively placed among the younginids. Galesphyrus capensis, also described by Broom in 1914 is from the base of the Cistecephalus assemblage zone of South Africa (thus older than Youngina) and is known from a partial postcranial skeleton. Heleosuchus griesbachi, originally described by Owen (1876) as a species of Saurosternon, is known from a single specimen consisting of the posterior part of the skull and a partial postcranial skeleton. The fossil was thought to be lost until relocated in the Natural History Museum in Vienna, Austria (Carrol, 1987). The specimen is from South Africa from an unknown horizon and would date either from the Late Permian or the Early Triassic. Without good skull material, getting the exact affinities of these two animals is very difficult.

Fig 4.- Reconstruction of Thadeosaurus colcanapi.

From the Lower Sakamena formation of southern Madagascar originates Thadeosaurus colcanapi (Carroll, 1981) which is based on two nearly complete skeletons missing the skull and the lower parts of the limbs. This one was originally thought to belong to the European genus Datheosaurus, which is now known to be synonymous with the pelycosaur Haptodus (thus a Synapsid … it seems many of these early diapsids were first mistaken with a synapsid). As an intended pun, the name Thadeosaurus is simply an anagram of the name Datheosaurus, the only deliberate anagram of an animal scientific name that I am aware of. Thadeosaurus is known from several specimens, including juveniles, many being at first confused with the Tanzanian Tangasaurus (Currie & Carrol, 1984). It was a small lizard like creature measuring perhaps about 60 cm in length and characterized by a very long tail. Although found in marine strata, Thadeosaurus has no obvious adaptation for swimming indicating it was most probably a coastal fully terrestrial animal. The interesting thing about the Lower Sakamena formation is that this aquatic deposit contains an unusually large proportion of diapsid reptiles as compared to any other upper Permian deposits in the world. This is quite anomalous and the exact age of the deposits can be questioned. The age is based on palynological (fossil pollen) evidence and correlation of the vertebrate fauna with South Africa. One index fauna is the procolophonid Barasaurus which is similar to the South African Owenetta. But the latter was later also found in Early Triassic strata.

Let us conclude this tour of the terrestrial younginiformes with Kenyasaurus mariakanensis from the Early Triassic Maji-Ya-Chumvi formation of Kenya (Harris & Carroll, 1977). It is known from a single specimen lacking the skull and most of the pectoral girdle and forelimb, making its affinities hard to establish. This one was recently kicked out of the younginiformes. Like Thadeosaurus, it was found in marine strata but does not appear to have any specialization for aquatic environment. Therefore, it was probably a terrestrial form which measured about 50 cm in length.

Note also that two animals of that time, Heleosaurus and Apsisaurus, once considered being younginiformes turn out to be Synapsids of the varanopid sort.

Next, the marine “younginiformes”…

References:

Carroll, R. (1981). Plesiosaur ancestors from the Upper Permian of Madagascar. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, 293(1066), 315-383.

Carroll, R. (1987). Heleosuchus: An enigmatic diapsid reptile from the Late Permian or Early Triassic of southern Africa. Canadian Journal of Earth Sciences, 24, 664-667.

Currie, P., & Carroll, R. (1984). Ontogenetic changes in the eosuchian reptile Thadeosaurus. Journal of Vertebrate Paleontology, 4(1), 68–84.

Harris, J., & Carroll, R. (1977). Kenyasaurus, a new eosuchian reptile from the Early Triassic of Kenya. Journal of Paleontology, 51(1), 139-149.

Modesto, S., & Reisz, R. (2003). An enigmatic new diapsid reptile from the Upper Permian of Eastern Europe. Journal of Vertebrate Paleontology, 22(4), 851-855.

Olson, E. (1936). Notes on the skull of Youngina capensis Broom. The Journal of Geology, 44(4), 523-533.

Reisz, R. R., Modesto, S. P. and Scott, D. M. (2011). A new Early Permian reptile and its significance in early diapsid evolution. Proceedings of the Royal Society B 278, 3731-3737

Smith, R., & Evans, S. (1996). New material of Youngina: evidence of juvenile aggregation in Permian diapsid reptiles. Palaeontology, 39(2), 289-303.

2012 in Paleontology

2013-01-01T17:25:00.000-08:00

It’s time for a retrospective of year 2012 in the paleontological field. Many species were described that year and apart from a few obvious ones, it was quite difficult to decide what should make up the top ten stories. After multiple hesitations, here is my pick (not in particular order of importance):

1.- The Kelheim theropod unveiled in 2011 received its official scientific name as Sciurumimus albersdoerferi. More surprisingly, it turns out to be a Megalosauroid, making it the theropod the most distantly related to birds to show direct evidence of feathers.

Reference: O. W. M. Rauhut, C. Foth, H. Tischlinger and M. A. Norell. 2012. Exceptionally preserved juvenile megalosauroid theropod dinosaur with filamentous integument from the Late Jurassic of Germany. Proceedings of the National Academy of Sciences 29:11746-11751.

2.- At 9 meter in length, Yutyrannus huali is the largest dinosaur showcasing direct evidence of feathers. Yutyrannus is also a tyrannosauroid, moving the at least partial feather coverage idea for Tyrannosaurus rex, from good probability to almost certainty.

Reference: X. Xu, K. Wang, K. Zhang, Q. Ma, L. Xing, C. Sullivan, D. Hu, S. Cheng, and S. Wang. 2012. A gigantic feathered dinosaur from the Lower Cretaceous of China. Nature 484:92-95

3.- Echinoderms (starfish, urchins, sea lilies, etc…) are unique among animals in having a body with a fivefold symmetry. We know from embryology that they must have evolved from bilateral ancestors. The fossil record finally confirmed this with the discovery of Ctenoimbricata spinosa, a sea floor spiny animal which proved to be an early echinoderm with bilateral symmetry.

Reference: S. Zamora, I. A. Rahman, and A. B. Smith. 2012. Plated Cambrian Bilaterians Reveal the Earliest Stages of Echinoderm Evolution. PLoS ONE 7(6):e38296:1-e38296:11.

4.- Microraptor, the four-winged dinosaur that already made the headlines last year when it was discovered to feed on birds, reveals its true colors: the study of fossil pigments indicates it had the plumage of a crow: metallic black.

Reference: Q. Li. 2012. Reconstruction of Microraptor and the Evolution of Iridescent Plumage. Science 335: 1215-1219.

5.- Evidence of feathers was also found in the North American ostrich-mimic dinosaur Ornithomimus edmontonicus. While the body was covered with downy feathers, the arms in the adults had wing feathers, suggesting that mating display was the initial purpose of those, not flight.

Reference: D. K. Zelenitsky, F. Therrien, G. M. Erickson, C. L. Debuhr, Y. Kobayashi, D. A. Eberth, F. Hadfield, 2012. Feathered Non-Avian Dinosaurs from North America Provide Insight into Wing Origins. Science 338 (6106): 510.

6.- Mosasaurs form a group of highly specialized predators from the Late Cretaceous period, related to modern day monitor lizards and perfectly adapted for swimming. The fossil of Pannoniasaurus inexpectatus is the first evidence that these predominantly marine creatures have also conquered freshwater.

Reference: L. Makádi, M. W. Caldwell, and A. Osi. 2012. The first freshwater mosasauroid (Upper Cretaceous, Hungary) and a new clade of basal mosasauroids. PLoS ONE 7(12):e51781.

7.- Nyasasaurus parringtoni known from very fragmentary remains might have been the earliest representative of the dinosaur clade.

Reference: S. J. Nesbitt, P. M. Barrett, S. Werning, C. A. Sidor, and A. J. Charig. 2013. The oldest dinosaur? A Middle Triassic dinosauriform from Tanzania. Biology Letters 9(1):1-5.

8.- A morphometric study of archosaur skulls indicate that birds have the skull of baby dinosaurs. Our avian friends may have therefore evolved from neotenic dinosaurs retaining their juvenile characteristics through adulthood.

Reference: Bhullar, B., Marugán-Lobón, J., Racimo, F., Bever, G., Rowe, T., Norell, M., & Abzhanov, A. 2012. Birds have paedomorphic dinosaur skulls. Nature, 487, 223-226.

9.- A new phylogenetic analysis of the enigmatic Miocene creature known as Necrolestes patagonensis indicates that it was a survivor of an ancient lineage of primitive mammals thought to have disappeared at the end of the Cretaceous: the Meridiolestids.

Reference: G. W. Rougier, J. R. Wible, R. M. D. Beck and S. Apesteguía. 2012. The Miocene mammal Necrolestes demonstrates the survival of a Mesozoic nontherian lineage into the late Cenozoic of South America. Proceedings of the National Academy of Sciences of the United States of America 109 (49): 20053–20058.

10.- The Cetotheriids are a family of baleen whales that appeared during the Late Oligocene and thought to be extinct since the Late Pliocene. Not anymore: a new phylogenetic analysis indicates that the living Pygmy Right Whale (Caperea marginata) is in fact a modern surviving representative of this family.

Reference: R. E. Fordyce and F. G. Marx. 2013. The pygmy right whale Caperea marginata: the last of the cetotheres. Proceedings of the Royal Society B: Biological Sciences 280 (1753): 20122645.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com)

Humble beginnings for the mighty diapsids: the Araeoscelids and Orovenator

2012-12-02T12:46:00.001-08:00

The amniotes (those initially four-legged creatures that produce "amniotic eggs", i.e. eggs adapted for land life) are traditionally divided into a few branches depending on some key characteristics of their skull, and the diapsids appear to be the most successful of all these branches. Virtually all living vertebrates that we commonly name "reptiles" are diapsids: crocs, lizards, snakes, the whole lot of them... Diapsids also include the birds by way of their forebears, the dinosaurs. In contrast, mammals and their ancestors belong to the synapsid branch of the amniotes. The distinction between diapsid and synapsid lays in the number of holes (scientist called those "fenestrae" which means windows) in the skull just behind the eye socket. Diapsids typically have two, the supratemporal (or upper temporal) fenestra on top and the infratemporal (or lower temporal) fenestra below. Synapsids only have one, the bottom infratemporal fenestra, simply called temporal fenestra. Both diapsids and synapsids evolved from more primitive reptiles with no opening behind the eye: the anapsids. The distinction between the different type of skulls are depicted in Figure 1.

Fig 1.- Different type of skulls among reptiles. Top left: anapsid skull of Procolophon trigonoceps (after Romer, 1956) top right: diapsid skull of Petrolacosaurus kansensis (after Reisz, 1981), bottom: synapsid skull of Eothyris parkeri (after Reisz et al., 2009).

The distinction seems simple enough but only reflects the primitive initial condition. Evolution indeed loves playing tricks. The same way that we know that dolphins are really mammals and not some strange air-breathing fish, scientists figured that everybody's favorite marine mesozoic reptiles, the plesiosaurs and ichthyosaurs, are really diapsids in disguise. Their skulls only have one opening behind the eye socket, the supratemporal fenestra, a condition which is called 'euryapsid'. The euryapsids used to be considered as a fourth branch of reptiles, but carefull examinations of the fossils show they evolved from diapsid ancestors and that the loss of the infratemporal fenestra is only a secondary characteristics. More tricky are the turtles. These do not have any opening behind the eye which classified them as "anapsids". However, nowadays, it seems quite firmly established that they too are highly modified diapsid reptiles, although it took scientists quite a while to figure this one out. Now look a the highly modified skulls of birds and snakes: you will have hard time recognizing any of the original temporal openings in them, but since their ancestors were diapsid reptiles, by way of basic phylogeny law (you shall belong to the same clade as your ancestors, ... i.e the monophyly principle), they too are diapsid reptiles.

That being said, the diapsids then really are the most successful group of amniotes with some 18,000 species, including birds, alive today (compared to the 5700 species of mammals representing the only survivors of the synapsid branch). But what is their origin? They probably evolved during the Late Pennsylvanian from a group of anapsid ancestors to which such lizard-like creatures as Paleothyris and Hylonomus belong to. But this is not at all very clear because of the scarcity of the fossil record. The first true diapsids are a family of small superficially lizard-like creatures called Araeoscelidia, to which Petrolacosaurus and Araeoscelis are the best known representatives. The fossil record of the Araeoscelids extends from the Late Carboniferous to the Early Permian.

Fig 2.- a reconstruction of Petrolacosaurus kansensis.

The most ancient known diapsid is Petrolacosaurus kansensis from the Late Pennsylvanian (the North American 'Missourian' stage which corresponds to the ICS Kasimovian stage, ~305 MYA) of Kansas. The generic name means "rock lake reptile" in reference to the "Rock Lake Shale" in which the type specimen (a nearly complete hind limb) was found. Although originally described in 1945 as a pelycosaur (thus a synapsid), it was not until 1977 after new specimens including the skull with its two characteristic openings, were thoroughly described, that it was realized to be the earliest known diapsid, raising the little critter from relative obscurity to paleontological stardom. In a world dominated by giant arthropods and fearful amphibians, Petrolacosaurus was indeed relatively small, measuring probably about 70 to 80 cm in length, accounting for the long tail.

Fig 3.- Reconstruction of Spinoaequalis schultzei.

Also from the Late Pennsylvanian of Kansas but a bit later (from the Calhouns Shale formation dated to the North American 'Virgilian' stage roughly corresponding to the ICS Gzhelian, ~ 300 MYA), comes Spinoaequalis schultzei. This early diapsid is a bit smaller (30 cm) and is only tentatively placed among the araeoascelids. The interesting note about this critter is the tail: the tall and equal size neural and haemal spines of the caudal vertebra (thus the generic name) which gives the distinct tall and laterally compressed shape to the tail is viewed as an adaptation for swimming, a good indication that Spinoaequalis was an aquatic animal. This is supported by the fact that its fossil was discovered in freshwater deposits among remains of spiny sharks (acanthodians) and other fully aquatic animals. However, the long and slender limbs, are those of a terrestrial animal, an indication that it wasn't fully aquatic. In any case, this makes Spinoaequalis the first amniote to have ever returned to water since their epic conquest of the dry lands.

Fig 4.- Skulls of Araeoscelis gracilis (after Reisz et al., 1984).

Araeoscelis dates from the Early Permian and was originally described in 1910 as a lizard. It has the same body plan than Petrolacosaurus but the skull was more massive with strong teeth, ideal for crushing the heavy exoskeleton protecting some of the arthropods of that time. Araeoscelis was about the same size too, with an estimated length of 70-80 cm accounting for the unknown tail. As a probable adaptation of its specialized diet, the lower temporal fenestra has closed making the skull more robust. Araeoscelis, has therefore this 'euryapsid' condition that will be common to the large marine predators of the Mesozoic. Two species have been described, A. gracilis from the Arroyo Formation of Texas (Kungurian age, ~275 MYA), known from several fairly complete specimens, and A. casei from the Admiral Formation of Texas (Artinskian age, ~285 MYA), known from at least seven individuals. The two are virtually indistinguishable and the separation into distinct species seems only to be justified by their difference in age, A. casei being from slightly (~ 10 millions years) older rocks than A. gracilis.

Fig 5.- Reconstruction of Araeoscelis gracilis.

The other Araeoscelids are poorly known and all date from the Early Permian. The 70 cm long Dictybolos tener from the Wellington formation of Oklahoma (~280 MYA) is known from isolated bones from numerous individuals. This one was presumably semi-aquatic and a fish eater. Zarcasaurus tanyderus from the Cutler Formation of New Mexico is known from a partial disarticulated skeleton. Characterized by its rather long neck vertebrae, it was a close relative of Araeoscelis. In Europe, the rather dubious Aphelosaurus lutevensis from the Tuilières formation of South Central France and first described in the 19th century, is another possible Araeoscelid, though it is hard to tell without any knowledge of a crucial piece of fossil information: the skull. Similarly, Kadaliosaurus priscus from the Rotliegend of Germany is only known from a postcranial skeleton and its classification among the araeoscelids is only tentative.

Fig 6.- Reconstructed skull of Orovenator mayorum (after Reisz et al., 2011).

Besides the Araeoscelids, there is one additional diapsid dating from the Early Permian, Orovenator mayorum discovered in one of the fissure fills of the Richards Spur locality of Oklahoma, and known from two partial crushed skulls. Orovenator has the distinction of being the earliest known and most primitive of the Neodiapsids, a clade that contains all the known diapsids except for the araeaoscelids. This was a small animal with an elongated skull half the length of those of Petrolacosaurus and Araeoscelis. The Richards Spur locality with its distinct Early Permian fauna of some 30 taxa of fully terrestrial vertebrates, is thought to originate from an upland ecosystem, which would only fossilized in very exceptional cases. This is in sharp contrast to the Araeoscelids which were all found in lowland swampy habitats, with better chances for fossilization. The hypothesis is therefore that the initial split of the early diapsids into the Araeoscelids and the Neodiapsids is the result of adaptation to two different habitats, with the Araeoscelids in the lowlands and the Neodiapsids in the uplands.

In conclusion, the early diapsids show a surprising degree of diversity with some forms that became at least partially aquatic (Spinoaequalis, Dictybolos) while others adapted to the harsher conditions of the uplands (Orovenator). There is also evidence of a quite specialized diet for some (Araeoscelis). However, the remains of these animals are quite rare and there is a rather long gap in the fossil record before we see them appear again in the Late Permian. Their number would not significantly increase before the Early Triassic. It is somewhat tempting to imagine that like the mammals of the Mesozoic dominated by the dinosaurs, the early diapsids lived in the relative shadow of the other reptiles for some 50 million years, when the world was dominated by larger synapsids, anapsids and amphibians and that it will take the massive Permian-Triassic extinction event to see the diapsids finally take the upper hand.

References:

Brinkman, D., Berman, D., & Eberth, D. (1984). A new araeoscelid reptile, Zarcasaurus tanyderus from the Cutler Formation (Lower Permian) of north-central New Mexico. New Mexico Geology, 34–39.

Debraga, M., & Reisz, R. (1995). A new diapsid reptile from the uppermost carboniferous (Stephanian) of Kansas. Palaeontology, 38(1), 199–212.

Lane, H. (1945). New mid-Pennsylvanian reptiles from Kansas. Transactions of the Kansas Academy of Science (1903-), 47(3), 381–390.

Olson, E. (1970). New and little known genera and species of vertebrates from the Lower Permian of Oklahoma. Fieldiana: Geology, 18(3), 359–434.

Reisz, R. R. (1977). Petrolacosaurus, the oldest known diapsid reptile. Science, 196(4294), 1091–3.

Reisz, R., Berman, D., & Scott, D. (1984). The anatomy and relationships of the Lower Permian reptile Araeoscelis. Journal of Vertebrate Paleontology, 4(1), 57–61.

Reisz, R. R., Modesto, S. P., & Scott, D. M. (2011). A new Early Permian reptile and its significance in early diapsid evolution. Proceedings. Biological sciences / The Royal Society, 278(1725), 3731–7.

Williston, S. (1910). New Permian reptiles: rhachitomous vertebrae. The Journal of Geology, 18(7), 585–600.

Williston, S. (1913). The skulls of Araeoscelis and Casea, Permian reptiles. The Journal of Geology, 21(8), 743–747.

Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com)