Tuesday, June 24, 2008

A ratty old sauropodomorph caudal

Meet BP/1/5339 another James Kitching find, this time a lone sauropodomorph caudal vertebra from the lower Elliot Formation (Late Triassic). It isn’t brilliantly preserved, nor has it been properly prepared yet but it is worthy of note because it is BIG. The anterior centrum face is 232 mm high and 194 mm wide, while in side view the centrum is 138 mm long. Granted this vertebra probably comes from the base of the tail where the caudal vertebrae are at their largest but it isn’t the first vertebra. There are chevron facets both fore and aft, indicating that this is at least the second caudal, or more probably the third. Compare its size to a comparable caudal (ca II) from NSMT-PV 20375, an Apatosaurus ajax (data from Upchurch et al. 2004). In this specimen the same measurements are 230, 240 and 134, respectively. I think you will agree that the two specimens are closely similar in size, although the apatosaur has transversely wider centra. This means that the Triassic of South Africa was harbouring a sauropodomorph whose tail base, at least, was similar in size to that of one of the larger Morrison neosauropods. I find that .....unexpected, to say the least. So what species does the caudal belong to? That’s another good question without a good answer. The basal sauropod Antetonitrus ingenipes is a plausible candidate. The holotype includes proximal caudals that are quite a bit smaller than BP/1/5339 but it is a juvenile. Most features of Antetonitrus are in agreement this specimen but this does not include any specific diagnostic characters. One difference that may be of significance is the strongly concave nature of the anterior centrum face of BP/1/5339, which is comparable to the procoelous caudals of advanced titanosaurs (the posterior face remains flat however). Maybe this could be a diagnostic character, or maybe it is the result of postmortem collapse. The answer is hopefully out there in the relatively unexplored exposures of the Elliot Formation.


Upchurch P, Tomida Y, Barrett PM (2004) A new specimen of Apatosaurus ajax (Sauropoda: Diplodocidae) from the Morrison Formation (Upper Jurasic) of Wyoming, USA. National Science Museum Monographs 26: 1-107.

1 comment:

Mike Taylor said...

Wow. That is amazing, especially when you bear in mind that the tail of Apatosaurus (and diplodocids in general) is proportionally very large. Other things being equal, it looks like you have yourself a sauropodomorph from the freakin' Triassic already that is bigger overall than a good-sized Apatosaurus.