THE OSTEOLOGY OF HAYA GRIVA (DINOSAURIA: ORNITHISCHIA) FROM THE LATE CRETACEOUS OF MONGOLIA DANIEL E. BARTA AND MARK A. NORELL BULLETIN OF THE AMERICAN MUSEUM OF NATURAL HISTORY THE OSTEOLOGY OF HAYA GRIVA (DINOSAURIA: ORNITHISCHIA) FROM THE LATE CRETACEOUS OF MONGOLIA DANIEL E. BARTA Department of Anatomy and Cell Biology Oklahoma State University College of Osteopathic Medicine at the Cherokee Nation, Tahlequah, OK; and Richard Gilder Graduate School and Division of Paleontology, American Museum of Natural History, New York MARK A. NORELL Division of Paleontology American Museum of Natural History, New York BULLETIN OF THE AMERICAN MUSEUM OF NATURAL HISTORY Number 445, 111 pp., 58 figures, 1 table Issued February 26, 2021 Copyright © American Museum of Natural History 2021 ISSN 0003-0090 CONTENTS Abstract.............................................................................3 Introduction.........................................................................3 Material and methods ................................................................3 Institutional acronyms . 4 Systematic paleontology...............................................................5 Taphonomy..........................................................................7 Description..........................................................................7 Skull and mandible . 7 Axial skeleton ....................................................................45 Appendicular skeleton.............................................................61 Gastroliths .........................................................................77 Histology ..........................................................................77 Phylogeny ..........................................................................84 Discussion .........................................................................89 Ontogenetic and other intraspecific variation.........................................89 Phylogenetic position of Haya griva . 93 Summary ..........................................................................94 Acknowledgments...................................................................94 References..........................................................................95 Appendix 1: Anatomical abbreviations . 102 Appendix 2: Character list for phylogenetic analyses ................................... 103 Supplement available online ..............................(https://doi.org/10.5531/sd.sp.47) 2 ABSTRACT Haya griva is an early-diverging neornithischian (“hypsilophodontid”) dinosaur known from several well-preserved skulls and articulated postcranial skeletons, in addition to dozens of partial or isolated finds from the Upper Cretaceous Khugenetslavkant and Zos Canyon localities (Javkhlant Formation and equivalent beds) in the Gobi Desert of Mongolia. Collectively, nearly the entire skeletal anatomy of Haya is known, including partial growth series of skulls and femora. Detailed description and comparisons with other ornithischians, including novel anatomical information about the palate and braincase gleaned through high-resolution x-ray microcomputed tomography, reveals a wealth of osteological data for understanding the growth and relationships of this key taxon. Though theHaya specimens span a wide size range, bone histology reveals that all are likely perinatal to subadult individuals, with specimens of intermediate age the most common, and skel- etally mature specimens absent. Phylogenetic analyses place Haya as one of the few Asian members of Thescelosauridae, an important noncerapodan neornithischian group of the Late Cretaceous. INTRODUCTION parative anatomical knowledge of early-diverg- ing neornithischians. The combination of The ornithischian dinosaurHaya griva holds character states described in Haya provides fur- great evolutionary, systematic, biostratigraphic, ther information for attempts to resolve the and paleoecological significance. It is the only unstable relationships and complex, mosaic dis- representative of an early-diverging ornithis- tribution of characters within clades along this chian dinosaur currently known among the vast grade (Boyd, 2015). In order to provide a thor- diversity of Mesozoic vertebrates from Mongo- ough account of the morphology, growth, sys- lia’s Gobi Desert. Despite previous expeditions tematics, and probable life habits of Haya griva, to the Upper Cretaceous (Santonian-Campan- we apply high-resolution X-ray microcomputed ian) eastern Gobi exposures of the Javkhlant tomography (µCT) scanning and bone histol- Formation (Shine Us Khudag redbeds) at the ogy to a partial growth series of this taxon for Khugenetslavkant locality (Eberth et al., 2009; the first time, reassess its phylogenetic affinities, fig. 1) by Russian, Mongolian, and American and further evaluate the implications of gastro- paleontologists, the presence of a primitive liths associated with three specimens. neornithischian dinosaur at this site was not revealed until the first discovery of its fossils in 2002 by the joint Mongolian Academy of Sci- MATERIAL AND METHODS ences–American Museum of Natural History The holotype and referred specimens col- expedition (Makovicky et al., 2011). Makovicky lected by the Mongolian Academy of Sciences– et al. (2011) named and described Haya griva American Museum of Natural History (MAE) on the basis of an articulated holotype skull and expeditions listed below form the basis of this several referred specimens consisting of articu- description. lated and partially articulated cranial and post- Four Haya griva skulls (IGM 100/2016, IGM cranial remains. We extensively describe these 100/2017, IGM 100/3178, IGM 100/3181) were materials and another specimen (IGM scanned using high resolution X-ray micro- 100/3181) first presented by Norell and Barta computed tomography (µCT) at the American (2016). We also describe six new nearly com- Museum of Natural History Microscopy and plete or partial specimens of Haya griva, and Imaging Facility (MIF) with a GE v|tome|x CT compare them to other ornithischian dinosaurs, scanner at 160 kv, with a 0.5 mm copper filter, particularly those for which excellent material a current of 200 µA, and a voxel dimension of also exists. Such comparisons enhance com- 0.04 mm to produce 1800 images. All of these 3 4 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 445 FIG. 1. Map of Mongolia showing the Khugenetslavkant and Zos Canyon localities. except IGM 100/3181, which was not processed INSTITUTIONAL ACRONYMS for this study, were reconstructed using Phoe- nix Datos X (GE Inspection Technologies, LP, AMNH FARB American Museum of Natural Lewistown PA) and FIJI (ImageJ, Schindelin et History Fossil Amphibians, Rep- al., 2012) software, and features of interest were tiles, and Birds Collection segmented with VGStudio Max (Volume BYU Earth Sciences Museum, Graphics, Inc. Charlotte, NC). Key specimens Brigham Young University, (IGM 100/1324, IGM 100/2014, IGM 100/2015, Provo, Utah IGM 100/2016, IGM 100/2017, IGM 100/2019, IGM Institute of Geology, Mongolian IGM 100/2020, IGM 100/3137, IGM 100/3178, Academy of Sciences, Ulaan IGM 100/3181, and IGM 100/3661) were sur- Baatar, Mongolia face scanned with a Space Spider surface scan- ROM Royal Ontario Museum, ner (Artec, Luxemborg). Stereolithography Toronto, Ontario, Canada (STL) files of these specimens are provided as MOR Museum of the Rockies, Boze- supplementary information available online man, Montana (https://doi.org/10.5531/sd.sp.47). Bone histol- YPM Yale Peabody Museum of Natu- ogy and phylogenetic analysis methods are ral History, New Haven, Con- described in the relevant sections below. necticut 2021 BARTA AND NORELL: OSTEOLOGY OF HAYA GRIVA 5 SYSTEMATIC PALEONTOLOGY IGM 100/3137 (fig. 29), articulated postcrania lacking skull. Dinosauria Owen, 1842 IGM 100/3178 (figs. 7, 32, 36, 39, 40, 45, 46, 48), Ornithischia Seeley, 1887 skull (CT scanned) and partially articulated postcrania. Neornithischia Cooper, 1985 (sensu Sereno, IGM 100/3181 (fig. 8), skull (CT scanned) and 1998) articulated dorsal series with ribs, manual Haya Makovicky et al., 2011 phalanges, radius and ulna (Norell and Barta, 2016). Haya griva Makovicky et al., 2011 IGM 100/3182 (fig. 50), partial postcrania, Etymology: “Haya griva, from the Sanskrit including a largely complete left leg, some for the Hindu deity Hayagriva, an avatar of dorsal vertebrae, and associated gastroliths. Vishnu characterized by a horse head, in refer- IGM 100/3557 (fig. 12), crushed partial skull. ence to the elongate and faintly horselike skull of IGM 100/3661 (fig. 14), disarticulated partial this dinosaur, and the common depiction of this skull and skeleton. deity in the Buddhist art of Mongolia” (fig. 2) IGM 100/3672 (fig. 15), partial pelvic region and (Makovicky et al., 2011: 626). articulated legs and feet from two individuals Holotype: IGM 100/2017 (figs. 3–5, 17A, in close proximity, centra of the axis and third 18A, 21–26A, 30), complete articulated skull (CT cervical vertebra, a jaw fragment and other scanned) and anterior cervical vertebrae. surface collected fragments, including a pos- Referred Specimens: sible atlantal neurapophysis. An isolated IGM 100/1324 (figs. 41, 51, 52), large isolated troodontid tooth was found in the matrix femur (the largest in the studied sample). inside the jacket during preparation (fig. 16). IGM 100/2013 (figs. 44, 47), “dorsal rib and MAE 15-84, isolated femur. series of chevrons, an articulated right crus Many additional specimens