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Kosmoceratops not present in Dinosaur Park Formation of Canada



Ben Creisler
bcreisler@gmail.com

New in PLoS ONE:

James A. Campbell, Michael J. Ryan, Robert B. Holmes & Claudia J.
Schröder-Adams (2016)
A Re-Evaluation of the Chasmosaurine Ceratopsid Genus Chasmosaurus
(Dinosauria: Ornithischia) from the Upper Cretaceous (Campanian)
Dinosaur Park Formation of Western Canada.
PLoS ONE 11(1): e0145805.
doi:10.1371/journal.pone.0145805
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0145805

Background

The chasmosaurine ceratopsid Chasmosaurus is known from the Upper
Cretaceous (Campanian) Dinosaur Park Formation of southern Alberta and
Saskatchewan. Two valid species, Chasmosaurus belli and C. russelli,
have been diagnosed by differences in cranial ornamentation. Their
validity has been supported, in part, by the reported stratigraphic
segregation of chasmosaurines in the Dinosaur Park Formation, with C.
belli and C. russelli occurring in discrete, successive zones within
the formation.

Results/Conclusions

An analysis of every potentially taxonomically informative
chasmosaurine specimen from the Dinosaur Park Formation indicates that
C. belli and C. russelli have indistinguishable ontogenetic histories
and overlapping stratigraphic intervals. Neither taxon exhibits
autapomorphies, nor a unique set of apomorphies, but they can be
separated and diagnosed by a single phylogenetically informative
character—the embayment angle formed by the posterior parietal bars
relative to the parietal midline. Although relatively deeply embayed
specimens (C. russelli) generally have relatively longer postorbital
horncores than specimens with more shallow embayments (C. belli),
neither this horncore character nor epiparietal morphology can be used
to consistently distinguish every specimen of C. belli from C.
russelli.

Status of Kosmoceratops in the Dinosaur Park Formation

Kosmoceratops is purportedly represented in the Dinosaur Park
Formation by a specimen previously referred to Chasmosaurus. The
reassignment of this specimen to Kosmoceratops is unsupported here, as
it is based on features that are either influenced by taphonomy or
within the realm of individual variation for Chasmosaurus. Therefore,
we conclude that Kosmoceratops is not present in the Dinosaur Park
Formation, but is instead restricted to southern Laramidia, as
originally posited.