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Ceratosaurus forearm and manus described



Ben Creisler
bcreisler@gmail.com


A new paper:


Matthew T. Carrano & Jonah Choiniere (2016)
New information on the forearm and manus of Ceratosaurus nasicornis
Marsh, 1884 (Dinosauria, Theropoda), with implications for theropod
forelimb evolution.
Journal of Vertebrate Paleontology.
DOI: 10.1080/02724634.2015.1054497.
http://www.tandfonline.com/doi/full/10.1080/02724634.2015.1054497

Here we describe the forearm and manus of the ceratosaurian theropod
dinosaur Ceratosaurus nasicornis Marsh, 1884, from the Upper Jurassic
Morrison Formation of the western U.S.A. Recently removed from
exhibition and reprepared, the holotype offers important new
information on the morphology of this taxon that bears on the
evolution of the forelimb in nonavian theropod dinosaurs more
generally. The ulna and radius show particular similarities to those
of Dilophosaurus and Eoabelisaurus but lack features that characterize
derived abelisaurids. In the manus, Ceratosaurus bears short first
phalanges, like more derived taxa in the clade, but retains
metacarpals that are much more similar to those of Dilophosaurus,
Berberosaurus, and Eoabelisaurus. Taken together, and incorporated
with existing phylogenetic data on other ceratosaurs, these data are
consistent with the placement of Ceratosaurus as close to
Abelisauroidea but basal to Eoabelisaurus. More importantly, they
strongly imply that the extremely reduced manus of Limusaurus is a
derived condition that does not reflect the primitive state for
Ceratosauria and therefore that Averostra is not the most likely
placement for a shift in manus digit identity during theropod
evolution. Finally, digit reduction began in ceratosaurs that still
possessed most phalanges and unguals, and we infer that grasping would
have been retained as a primary, if reduced, function in these forms.