One crazy Sauropterygian

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)

Rhomaleosaurus cramptoni

A friend of mine has asked me for a reconstruction of Rhomaleosaurus cramptoni to illustrate a book he is writing on prehistoric animals from England. R. cramptoni is one of these marine reptiles belonging to a group called plesiosaurs. It lived during the Early Jurassic in the shallow sea that was covering most of Western Europe at that time.


Plesiosaurs were traditionally divided into two morphology-based clades: the long-necked small-headed Plesiosauroidea (the plesiosaurs sensu stricto) with forms such as Plesiosaurus and Elasmosaurus, and the short-necked large-headed Pliosauroidea (the pliosaurs), represented by such animals as Kronosaurus and Liopleurodon of WWD fame.

Rhomaleosaurus and related taxa (the rhomaleosaurid family) were kind of oddballs among the plesiosaurs, as they combine features of the two morphotypes, i.e. they have relatively long necks and relatively large heads. A comprehensive phylogenetic analysis by Adam S.Smith and Gareth J. Dyke (2008) placed them firmly within the pliosaurs as sister group to the Leptocleidoidea and the Pliosauridae (pliosaur sensu stricto).


Rhomaelosaurus cramptoni, originally described in 1863 as a species of Plesiosaurus, was medium-size, measuring something like 7 meters in length. It is known from a complete skeleton of an adult specimen, which was unearthed in 1848 near Whitby, Yorkshire. Besides R. cramptoni, two other species are still tentatively recognized within the genus, R. zetlandicus and R. thorntoni, both from the Early Jurassic of England. The species R. propinquus is considered a junior synonym of R. cramptoni. “R. victor”  (Early Jurassic of Germany) was transferred in 2010  to  the new genus Meyerasaurus and “R. megacephalus” (Lower Jurassic, England) was found to be more closely related to Eurycleidus and Macroplata than to the other species of Rhomaleosaurus and will most likely be redescribed as a new genus in the near future.  Rhomaelosaurids were a remarkably shorted lived family, being present only in the Early and perhaps in the Middle Jurassic.

Proportions for my reconstruction is based on the skeletal published by A. S. Smith (2008).



References:

Carte A, Bailey WH. 1863. “Description of a new species of Plesiosaurus, from the Lias, near Whitby, Yorkshire”. J R Dublin Soc 4:160–170.

O’Keefe FR. 2001. “A cladistic analysis and taxonomic revision of the Plesiosauria (Reptilia: Sauropterygia)”. Acta Zool Fenn 213: 1–63.

Smith AS, Dyke GJ. 2008. “The skull of the giant predatory pliosaur Rhomaleosaurus cramptoni: implications for plesiosaur phylogenetics” Naturwissenschaften. 95, pp 975-980.

Smith AS, Vincent P. 2010. "A new genus of pliosaur (Reptilia: Sauropterygia) from the Lower Jurassic of Holzmaden, Germany". Palaeontology 53 (5): 1049–1063.

Taylor MA. 1992. Functional anatomy of the head of the large aquatic predator Rhomaleosaurus zetlandicus (Plesiosauria: Reptilia) from the Toarcian (Lower Jurassic) of Yorkshire, England. Philos Trans R Soc Lond Ser B 335:247–280.