Yinlong Research Articles

Postcranial anatomy of Yinlong downsi (Dinosauria: Ceratopsia) from the Upper Jurassic Shishugou Formation of China and the phylogeny of basal ornithischians

Ceratopsia includes some of the best-known ornithischian dinosaurs. Many species are erected based on cranial elements alone, and the postcranial skeletons are either missing or undescribed in many taxa. Here we provide the first detailed postcranial description of Yinlong downsi based on the holotype and eight other well-preserved skeletons. Yinlong downsi from the early Late Jurassic Shishugou Formation of the Wucaiwan area, Xinjiang, China, represents one of the most basal ceratopsians. The detailed study of the postcranial skeleton reveals one feature unique to it among ceratopsians: a blade-like prepubic process of the pubis with an elongate notch near its ventral margin. The postcranial material of Yinlong shares some unique features with that of the ornithischian Stenopelix valdensis from the Early Cretaceous of Germany, and provides further evidence that the latter is a basal ceratopsian. A comprehensive phylogenetic analysis of basal ornithischians was built based on 72 taxa and 380 characters. Most of the characters are illustrated for the first time in order to clarify character states. The new ornithischian phylogeny confirms that Yinlong belongs to Chaoyangsauridae. Chaoyangsaurids and Psittacosaurus form a monophyletic group that is sister to all other ceratopsians. The new phylogeny also supports Stenopelix valdensis as a basal ceratopsian, and Mosaiceratops to be close to Coronosauria. Additionally, the new phylogeny agrees with other recent analyses that place heterodontosaurids as the most basal ornithischians rather than with marginocephalians. Furthermore, Isaberrysaura, which has been hypothesized to be a basal ornithopod, is recovered as one of the most basal stegosaurs for the first time. The former ‘hypsilophodontid’ taxa are recovered within Ornithopoda rather than outside Cerapoda, and Jeholosauridae is shown to be valid in this analysis.

Correction: A New Taxon of Basal Ceratopsian from China and the Early Evolution of Ceratopsia

There is an error in the caption title for Fig 6, “The squamosal of Yinlong downsi (IVPP V18641).” Please see the complete, correct Fig 6 caption here. Fig 6 The squamosal of Hualianceratops wucaiwanensis (IVPP V18641).

Cranial anatomy of Yinlong downsi (Ornithischia: Ceratopsia) from the Upper Jurassic Shishugou Formation of Xinjiang, China

ABSTRACTYinlong 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/UJVPCitation for this article: Han, F.-L., C. A. Forster, J. M. Clark, and X. Xu. 2015. Cranial anatomy of Yinlong downsi (Ornithischia: Ceratopsia) from the Upper Jurassic Shishugou Formation of Xinjiang, China. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2015.1029579.

Evolutionary Transitions Among Dinosaurs: Examples from the Jurassic of China

Dinosaurs have captured the popular imagination more than any other extinct group of organisms and are therefore a powerful tool in teaching evolutionary biology. Most students are familiar with a wide variety of dinosaurs and the relative suddenness of their extinction, but few are aware of the tremendous longevity of their time on Earth and the richness of their fossil record. We first review some of the best-known groups of dinosaurs and discuss how their less-specialized relatives elucidate the path through which each evolved. We then discuss our recent discovery of Yinlong downsi, a distant relative of Triceratops, and other fossils from Jurassic deposits in China to exemplify how the continuing discovery of fossils is filling out the dinosaur family tree.