Sunday, February 8, 2015

Dickinsonia from the Ediacara biota


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.

Saturday, January 31, 2015

First among the synapsids: the ophiacodonts



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.

Tuesday, December 30, 2014

2014 in Paleontology





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.

Monday, November 3, 2014

Extraordinary Tanystropheus



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.

Monday, September 1, 2014

Meet the Chroniosuchians



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.

Sunday, July 20, 2014

Dinosaurs of the British Isles: the Book

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

Wednesday, May 21, 2014

Two late Scottish relatives of Jamoytius

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.