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1 January 2016 Cranial Anatomy of Yinlong downsi (Ornithischia: Ceratopsia) from the Upper Jurassic Shishugou Formation of Xinjiang, China
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Abstract
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.
© by the Society of Vertebrate Paleontology
Feng-Lu Han, Catherine A. Forster, James M. Clark and Xing Xu "Cranial Anatomy of Yinlong downsi (Ornithischia: Ceratopsia) from the Upper Jurassic Shishugou Formation of Xinjiang, China," Journal of Vertebrate Paleontology 36(1), (1 January 2016). https://doi.org/10.1080/02724634.2015.1029579
Received: 6 August 2014; Accepted: 1 February 2015; Published: 1 January 2016
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