Sunday, December 20, 2009

Vancleavea


Congrats yet again to Sterling Nesbitt and colleagues on the publication of another one of those insane Triassic hellasaurs, this time the surreal archosauriform*Vancleavea campi (Nesbitt et al. 2009) [adjacent life restoration by Sterling Nesbitt]. Vancleavea was named by Long & Murry (1995) and is well represented by various bits and pieces from the Upper Triassic of the southwestern USA (interestingly, it seems to have been around for a long time: like, 20 million years or so). Its affinities were initially unclear: all that was clear was that it was a weird, armoured diapsid reptile, with relatively small limbs and a covering of assorted osteoderms. But, as everyone knows, a new, very well preserved, articulated skeleton was later discovered at Ghost Ranch Quarry in New Mexico, and this is the specimen described in the new paper. Finally, we know what Vancleavea is, and what it looked like...

* Archosauriformes corresponds with Archosauria of tradition, with Archosauria now being restricted to the archosauriform crown-group (the crocodilian-bird clade).


Vancleavea was about 1.2 m long and, as is clear from the reconstruction shown here (from Nesbitt et al. 2009) was long-bodied and short-limbed. It was covered in rows of osteoderms, and 30 particularly tall osteoderms formed a vertical fin along the top of the tail. The latter is totally unique (archosauriformes, and reptiles [and tetrapods!] in general, tend to use elongated neural spines to increase the depth of the tail) and suggests that Vancleavea was a semi-aquatic swimming animal, and thus very different ecologically from other basal archosauriforms.

The skull is also really weird...


Check out the dorsally directed external nostril openings, the big caniniform fangs, and absence of a supratemporal fenestra (this absence is not primitive, but seems to represent secondary closure). Whether the animal is freakishly weird and disturbing, or beautiful and really cute, depends on your point of view. I intended here just to showcase a few pics: for more information check out Bill Parker's thoughts at Chinleana (Bill published on this taxon in 2008: Parker & Barton (2008)). Very, very cool - and yet more striking evidence for really profound diversity within the Triassic archosauriform assemblage.

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