Monday, December 14, 2015

Just What WAS Tanystropheus? Mark Whitton Answers

One of the most famous non-dinosaurian denizens of the Mesozoic is Tanystropheus, a spectacularly long-necked reptile which lived across Europe and Asia in Middle-Late Triassic times. We've known about this 5-6 m long animal since fragmentary fossils were pulled from Italian Triassic rocks in 1855, and now regard it as a particularly large and anatomically extreme member of the Protorosauria. This is a Permian-Triassic group of archosauromorphs (all reptiles more closely related to crocodylians and birds that lizards) that spawned numerous aberrant taxa, such as drepanosaurs, Sharovipteryx and Dinocephalosaurus. Within Protorosauria, Tanystropheus can be considered a tanystropheid, closely related to similar, but shorter-necked and smaller-bodied species such as Tanytrachelos and Langobardisaurus. Tanystropheus longobardicus is by far the best known Tanystropheus representative, and the one we always think of when discussing this animal, but something like five Tanystropheus species have been named over the years. It is currently uncertain how many of these should be considered valid and, of those, which ones truly represent Tanystropheus and not some other type of protorosaur. There are hints that longobardicus might be the sole representative of this genus, but work on this is ongoing.

What sort of animal was the Triassic, long-necked Eurasian protorosaur Tanystropheus? As we discovered in the last post, the lifestyle of Tanystropheus remains controversial over a century after it was first discovered. There is near universal agreement that it ate swimming prey such as fish and squid, but opinion is divided over whether it was obligated to aquatic, swimming lifestyles because of the burden of its long neck, or whether it was a water margin specialist that plundered small prey from shorelines. Previously, we discussed a core argument for the aquatic hypothesis, that the Tanystropheus neck would over-balance the animal. Calculations presented in the last post suggested that the mass distribution of Tanystropheus is not as weird as we might think, and certainly less so than than that of another group of long necked reptiles we are confident lived out of water, the azhdarchid pterosaurs. Based on this very basic test, I expressed some skepticism about the neck being simply too heavy to permit a terrestrial existence.

In the second discussion, I want to look at some finer aspects of Tanystropheus anatomy and palaeontology, how they've been interpreted, and what they might mean for its lifestyle. There are several areas which are relevant here: what we know of Tanystropheus diet, the palaeoenvironmental context of Tanystropheus fossils, aspects of tail and limb anatomy, and of course, the functionality of its neck. There's a lot to get through here, so let's not waste any more time on preamble.

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