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Yinlong (Jurassic ceratopsian) cranial anatomy

Ben Creisler

A new paper:

Feng-Lu Han, Catherine A. Forster, James M. Clark & Xing Xu (2015)
Cranial anatomy of Yinlong downsi (Ornithischia: Ceratopsia) from the
Upper Jurassic Shishugou Formation of Xinjiang, China.
Journal of Vertebrate Paleontology (advance online publication)

Yinlong downsi, from the Upper Jurassic Shishugou Formation, Xinjiang,
northwestern China, is the oldest known ceratopsian dinosaur. Here we
provide a detailed description of the skull and mandible based on the
holotype, three partial skulls, and disarticulated materials from
several other specimens. Yinlong can be diagnosed by six
autapomorphies: a distinct fossa along the midline of the frontals; a
slit-like carotid canal bordered by laminae; premaxillary teeth with a
vertical wear facet and a basal shelf; a deep sulcus on the ventral
surface of the quadratojugal; large oval nodules concentrated on the
lateral surface of the jugal; and a squamosal with an expanded dorsal
surface and a long, constricted quadrate process. A detailed
comparison with other basal ceratopsians suggests that Yinlong downsi
may belong within Chaoyangsauridae. Yinlong also shares many derived
characters both with Psittacosaurus and neoceratopsians, suggesting
that character evolution in early ceratopsians is complex.
Additionally, a caniniform premaxillary tooth is present in one small
specimen (IVPP V18636), which may suggest sexual dimorphism or
individual variation.

SUPPLEMENTAL DATA—Supplemental materials are available for this
article for free at www.tandfonline.com/UJVP