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Re: Spinops sternbergorum: new centrosaurine
From: Ben Creisler
The paper is now available online (free pdf, of course):
Andrew A. Farke, Michael J. Ryan, Paul M. Barrett, Darren H. Tanke, Dennis R.
Braman, Mark A. Loewen, and Mark R. Graham (2011)
A new centrosaurine from the Late Cretaceous of Alberta, Canada, and the
evolution of parietal ornamentation in horned dinosaurs.
Acta Palaeontologica Polonica 56 (4), 2011: 691-702
In 1916, a centrosaurine dinosaur bonebed was excavated within the
Campanian−aged deposits of what is now Dinosaur Provincial Park, Alberta,
Canada. Specimens from this now−lost quarry, including two parietals, a
squamosal, a skull missing the frill, and an incomplete dentary, were purchased
by The Natural History Museum, London. The material was recently reprepared and
identified herein as a previously unknown taxon, Spinops sternbergorum gen. et
sp. nov. Based upon the available locality data and paleopalynology, the quarry
lies in either the upper part of the Oldman Formation or the lower part of the
Dinosaur Park Formation. The facial region of the partial skull is similar to
putative mature specimens of Centrosaurus spp. and Styracosaurus albertensis,
with short, rounded postorbital horncores and a large, erect nasal horncore.
Parietal ornamentation is consistent on both known parietals and is unique
among ceratopsids. Bilateral, procurved
parietal hooks occupy the P1 (medial−most) position on the dorsal surface of
the parietal and are very similar to those seen in Centrosaurus apertus.
Epiparietals in the P2 or possibly P3 position (lateral to P1) manifest as
extremely elongate, caudally directed spikes, unlike the condition in C.
apertus, S. albertensis, or any other “derived” centrosaurine. Cladistic
analysis suggests that S. sternbergorum is closely related to Centrosaurus and
Styracosaurus. Historically, based upon the condition in Styracosaurus and
related centrosaurines, it was assumed that the medial−most elongated spikes on
centrosaurine parietals correspond to the P3 epiparietal position. The
exception illustrated in the new taxon suggests that homologies of epiparietals
among basal centrosaurines (e.g., Albertaceratops and Diabloceratops) and
derived centrosaurines (e.g., Styracosaurus and “pachyrhinosaurs”) should be
reconsidered. The medially−placed,
caudally-directed “P3” process of basal centrosaurines may, in fact, be
homologous with P2.