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Uteodon Braincase Ressigned to Dryosaurus



Ben Creisler
bcreisler@gmail.com

A recent paper:

Kenneth Carpenter and Matthew C. Lamanna (2015)
The Braincase Assigned to the Ornithopod Dinosaur Uteodon McDonald,
2011, Reassigned to Dryosaurus Marsh, 1894: Implications for
Iguanodontian Morphology and Taxonomy.
Annals of Carnegie Museum 83(2): 149-165
doi: http://dx.doi.org/10.2992/007.083.0201
http://www.bioone.org/doi/abs/10.2992/007.083.0201


The braincase from the Upper Jurassic (lower Tithonian) Morrison
Formation of the Carnegie Quarry at Dinosaur National Monument (Utah),
which was assigned to the ankylopollexian iguanodontian ornithopod
dinosaur Uteodon aphanoecetes (Carpenter and Wilson, 2008) is actually
that of the dryosaurid iguanodontian Dryosaurus cf. D. altus (Marsh,
1878). The purported braincase autapomorphy of U. aphanoecetes,
occipital condyle projects farther ventrally than basal tubera, is an
artifact of damage to the latter structures in this specimen. The
newly identified braincase of Dryosaurus Marsh, 1894, reveals features
that are not easily observed in other specimens of this taxon, such as
well-developed fossae on the anterior surfaces of the paroccipital
processes and a spike-shaped parasphenoid that lacks the dorsal
process seen in Dysalotosaurus Virchow, 1919. The distinction of this
latter dryosaurid genus from Dryosaurus is here regarded as tentative.

The removal of the braincase in question from the hypodigm of U.
aphanoecetes substantially reduces the morphological difference
between this taxon and another ankylopollexian species, Camptosaurus
dispar (Marsh, 1879). Furthermore, some of the postcranial characters
used to support the proposed sister-taxon relationship of U.
aphanoecetes and Cumnoria prestwichii (Hulke, 1880) are based on
hypothetical reconstructions of selected skeletal elements of the
latter, or are more widespread within Ornithopoda. The ilium of
Cumnoria prestwichii cannot currently be distinguished from that of
Camptosaurus dispar based on known material. Indeed, the only
presently recognized autapomorphy of Cumnoria prestwichii is the small
size of the opening into the maxillary sinus on the dorsomedial side
of the maxilla (i.e., the intramaxillary fossa); in Camptosaurus
dispar, by contrast, this opening is large and occupies most of the
dorsomedial surface of the bone. This single feature is not considered
sufficient to warrant the continued separation of the genera
Camptosaurus Marsh, 1885, and Cumnoria Seeley, 1888. Similarly, the
anatomical differences between U. aphanoecetes and Camptosaurus dispar
are regarded as meriting distinction at the species rather than the
genus level. Consequently, the genera Cumnoria Seeley, 1888, and
Uteodon McDonald, 2011, are here regarded as junior subjective
synonyms of Camptosaurus Marsh, 1885 (Cumnoria as revised synonymy,
and Uteodon as new synonymy). The species Cumnoria prestwichii and
Uteodon aphanoecetes are returned to the genus Camptosaurus, as
Camptosaurus prestwichii, revised combination, and Camptosaurus
aphanoecetes, revised combination, respectively.