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.

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.