September JVP: Anchiceratops and Alamosaurus

[Brad McFeeters <archosauromorph2@hotmail.com>]

Mallon, J.C., R. Holmes, D.A. Eberth, M.J. Ryan & J.S. Anderson, 2011.  
Variation in the skull of *Anchiceratops* (Dinosauria, Ceratopsidae) from the 
Horseshoe Canyon Formation (Upper Cretaceous) of Alberta.  Journal of 
Vertebrate Paleontology 31(5): 1047-1071.


Abstract: *Anchiceratops* is a chasmosaurine ceratopsid from the Upper 
Cretaceous Horseshoe Canyon Formation (HCF) of Alberta. It is distinguished 
primarily by its unique parietosquamosal frill ornamentation and possibly by 
the presence of a ventrally flexed olfactory bulb of the brain. Although 
*Anchiceratops* is known from at least ten partial skulls, only two of these 
have been formally described. These skulls are not stratigraphically 
segregated, but they differ markedly in their proportions (e.g., supraorbital 
horncore and frill dimensions), causing previous authors to account for this 
disparity with reference to either interspecific or sexual differences. Both of 
these hypotheses assume that variation in *Anchiceratops* is dimorphic; 
however, this assumption has never been tested with reference to all available 
material. The present study describes all material from the HCF that can be 
positively attributed to *Anchiceratops*, and tests the assumption of 
dimorphism by subjecting this material to a series of morphometric analyses. We 
find no compelling evidence for dimorphism in *Anchiceratops*, although sample 
size is still too small for convincing statistical support. We conclude that 
there is a single, variable species of *Anchiceratops*, *A. ornatus*. Average 
sedimentation rates for the HCF suggest that *A. ornatus* is a particularly 
long-lived species compared with other ceratopsids (1.5–2.0 Ma), and the 
paleoecological implications of this are discussed. A cladistic analysis that 
includes the new data presented here indicates that *Anchiceratops* is more 
closely related to *Chasmosaurus* than to *Triceratops*, in contrast with 
previous studies.



D'emic, M.D., J.A. Wilson & T.E. Williamson, 2011.  A sauropod dinosaur pes 
from the latest Cretaceous of North America and the validity of *Alamosaurus 
sanjuanensis* (Sauropoda, Titanosauria).  Journal of Vertebrate Paleontology 
31(5):1072-1079.

Abstract: Complete sauropod pedes are rare in the fossil record, which has 
limited their use in systematics. We describe a nearly complete, large sauropod 
pes from the Maastrichtian-age Naashoibito Member of the Kirtland Formation of 
New Mexico, U.S.A., that bears synapomorphies of some eusauropod clades, such 
as the presence of metatarsal I with a wide shaft and laterally deflected pedal 
unguals. Novel pedal characters presented herein, such as the presence of an 
embayment on the proximomedial corner of metatarsal IV, suggest that the 
Naashoibito specimen likely belongs to a titanosauriform. Based on its 
provenance, the Naashoibito specimen likely belongs to the derived titanosaur 
*Alamosaurus sanjuanensis*, which is the only recognized Late Cretaceous 
titanosaur in North America. However, formal referral to *Alamosaurus* awaits 
discovery of overlapping materials with the holotype or definitively referred 
remains. The holotypic scapula of *Alamosaurus sanjuanensis* is diagnostic, 
providing a basis for referral of some other Maastrichtian North American 
titanosaur specimens to the genus. Confirmation of these referrals and the 
description of the pes presented herein augment the data relevant to the 
systematic problems that have historically surrounded *Alamosaurus*.