Basal ornithopods exhibit a very low diversity in Cretaceous deposits of Asia, with only two diagnostic taxa published to date. A new basal ornithopod, Haya griva, gen. et sp. nov., is described here based on several well-preserved specimens from the Late Cretaceous Javkhlant Formation of Mongolia. Haya is diagnosed by a unique combination of characters, some of which are also present in other Asian Cretaceous basal ornithopods such as a bifid caudal ramus of the jugal and a tapering and beveled predentary. Traits, such as presence of separate maxillary fenestra, otherwise only known in Hypsilophodon, show more homoplastic distributions. Phylogenetic analysis provides weak support for grouping Haya with the Chinese Cretaceous taxa Jeholosaurus and Changchunsaurus, suggesting a greater hidden diversity of such animals in Asia. The most complete prepared specimen of Haya exhibits a sizeable gastrolith mass, representing only the second occurrence among ornithopods.
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We thank members of the 2002–2007 AMNH-MAS expeditions for the discovery and excavation of the material described herein. We are grateful to L. Herzog, A. Shinya, and D. Wagner (FMNH) for their masterly preparation of the specimens. John Weinstein (FMNH) provided excellent photography, and the figures were skillfully crafted by Marlene Donnelly (FMNH) and Mick Ellison (AMNH). R. Butler kindly shared pre-publication versions of his papers on Changchunsaurus. We thank S. Kaal (SAM) and A. Milner (NHMUK) for specimen access. This research was supported by the U.S. National Science Foundation grants EAR 0418648 to P.J.M., and EAR AToL 0228693 to P.J.M. and M.A.N. TNT is kindly made available at no cost by the Willi Hennig Society. The specimens were collected under auspices of agreements between the AMNH and the Mongolian Academy of Sciences. Support for these expeditions was provided by the Division of Paleontology, AMNH. We are especially grateful to Raymond Metoyer and Loren Eade of the Loyola University Medical Center outpatient CT facility for their assistance with CT scanning and measurement. Careful reviews by R. Butler and C. Boyd improved the quality of the manuscript.