RE: GSA Abstracts Posted

[Tim Williams <twilliams_alpha@hotmail.com>]

Looks like _Seismosaurus_ has been cut down to size, both length-wise and 
taxonomically.  Lucas & co. revise the body length from 52 to 33m, and 
formally sink _Seismosaurus_ as a species of _Diplodocus_ (_D. hallorum_).

> REAPPRAISAL OF SEISMOSAURUS, A LATE JURASSIC SAUROPOD DINOSAUR FROM NEW
> MEXICO.  LUCAS, Spencer G.1, HERNE, Matthew C.2, HECKERT, Andrew B.3, HUNT, 
> Adrian
> P.1, and SULLIVAN, Robert M.4,

The holotype and only known specimen (NMMNH P-3690) of Seismosaurus hallorum 
Gillette is from the Upper Jurassic Brushy Basin Member of the Morrison 
Formation near San Ysidro, New Mexico. It consists of several dorsal 
vertebrae, several cervical and dorsal ribs, an incomplete pelvis, a sacrum, 
and ~ 20 caudal vertebrae including two chevrons. Axial length estimates of 
Seismosaurus of as much as 52 m have been used to identify it as the longest 
dinosaur. However, they are largely based on mistaken placement of the 
middle caudal vertebrae and do not stand up to close critical scrutiny. 
Instead, an axial length estimate of 33 m is well supported. A single 
(right) femur (NMMNH P-25079) found as float at the type locality was 
excluded from the type series but appears to belong to the same individual 
as the holotype. As preserved, this femur is ~1680 mm long, and compares 
well with a reconstructed skeleton based on the axial length estimate used 
here. The supposed 240 gastroliths of Seismosaurus have been revealed to be 
highly polished quartzite pebbles that lack an unambiguous skeletal 
association; they are stream-deposited cobbles of a channel-lag deposit. The 
taxonomic validity of Seismosaurus also is questionable. Many of the 
supposedly diagnostic features of the genus are those of the caudal 
vertebrae that are spurious artifacts of misplacing the middle caudals as 
vertebrae 20-27 although, in fact, they are vertebrae 12-19. This correct 
placement reveals a caudal morphology strikingly similar to that of 
Diplodocus. Other supposedly diagnostic characters of Seismosaurus can be 
summarized as a relatively robust pelvis that has an unusual distal 
expansion of the ischium. This expansion, however, appears to be pathologic 
and is not mirrored in the second ischium (prepared subsequently), and the 
differences in proportions between the pelves of Seismosaurus and Diplodocus 
are minor---most metric ratios differ by less than 10%. Therefore, we 
consider Seismosaurus to be a junior subjective synonym of Diplodocus, 
though a case can be made for recognizing the New Mexican fossil as a valid 
species of Diplodocus, D. hallorum.



> ABELISAUROID THEROPOD DINOSAURS FROM THE LATE CRETACEOUS OF EGYPT: EVIDENCE
> FOR GONDWANAN COSMOPOLITANISM
> SMITH, Joshua B.,

Recent paleogeographic and paleobiogeographic scenarios postulate the 
isolation of continental Africa throughout the Late Cretaceous. The absence 
of abelisauroid theropods from Upper Cretaceous African strata has been 
employed as evidence of hypothesized African isolation, with acknowledgement 
that the paucity of African abelisauroids may be related to sampling rather 
than to their actual absence from the continent. Here we report on a shed 
theropod tooth from the Upper Cretaceous (Campanian-?Maastrichtian, ~70Ma) 
Duwi (Phosphate) Formation of the Eastern Desert of Egypt that was referred 
to Megalosaurus crenatissimus (=Majungatholus atopus) in 1921. Stepwise 
discriminant function analyses (DA) using squared Mahalanobis distances (D2) 
and including eight size and shape variables were run to test for 
morphological congruence between the Egyptian tooth and the dental 
morphologies of 16 well-established theropod taxa. The DA correctly 
classified 96.1% of the teeth in the sample and assigned the tooth to the 
Malagasy abelisaurid Majungatholus (29.95 D2, p <.0001). Given that current 
paleogeographic reconstructions posit that Madagascar had attained its 
current position relative to Africa before the beginning of the Late 
Cretaceous, it is unlikely that the Egyptian tooth actually pertains to 
Majungatholus. Nevertheless, its classification as an abelisaurid 
constitutes the first definitive evidence of this clade from the 
post-Cenomanian Cretaceous of the African continent. This result, combined 
with recent discoveries of abelisauroids from ~95Myr and older rocks in 
Niger and Morocco and ~95Myr-old remains from the Bahariya Oasis of Egypt 
that share dental characters with the abelisauroid Masiakasaurus, indicate 
that Abelisauroidea was actually a diverse group in continental Africa 
during the Late Cretaceous, existing in multiple places for at least ~25Myr. 
These results suggest that abelisauroids may have been more cosmopolitan 
than demonstrated by previous evidence and that faunal communication between 
South America and Africa might have remained possible for longer than has 
been generally hypothesized.

_________________________________________________________________
Don?t just search. Find. Check out the new MSN Search! 
http://search.msn.click-url.com/go/onm00200636ave/direct/01/