Osteology and ontogeny of Early Cretaceous Philydrosaurus (Diapsida: Choristodera) based on new specimens from Liaoning Province,China |
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| Institution: | 1. School of Earth and Space Sciences, Peking University, Beijing 100871, China;2. Division of Paleontology, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024, USA;3. Shenyang Normal University, 253 Huanghebei Street, Shenyang 110034, China;4. Laboratory for Vertebrate Paleontology, University of Alberta, Edmonton T6G 2E9, Canada;1. Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, 100044, People’s Republic of China;2. CAS Center for Excellence in Life and Paleoenvironment, Beijing, 100044, People’s Republic of China;3. College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, 100049, People’s Republic of China;4. Canadian Museum of Nature, Ottawa, ON K1P 6P4, Canada;5. The George Washington University, Washington D.C, 20052, USA;6. Institute of Dinosaur Research, Fukui Prefectural University, Fukui, 910-1195, Japan;7. Fukui Prefectural Dinosaur Museum, Fukui, 911-8601, Japan;8. Yanji Municipal Bureau of Land and Resources, Yanji, 133001, People’s Republic of China;9. Yanji Paleontological Research Centre, Yanji, 133001, People’s Republic of China;10. Yanji Dinosaur Museum, Yanji, 133001, People’s Republic of China;1. Faculty of Earth Systems and Environmental Sciences & Korea Dinosaur Research Center, Chonnam National University, Gwangju 61186, Republic of Korea;2. CAS Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210008, China;3. University of Chinese Academy of Sciences, Beijing 100049, China;4. State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210008, China;1. Natural History Museum of Geneva, Department of Geology and Palaeontology, Route de Malagnou 1, CP 6434, CH-1211 Geneva 6, Switzerland;2. IPHEP, UMR CNRS 7262, Université de Poitiers, UFR SFA, 6, rue M. Brunet, TSA 51106, 86073 Poitiers Cedex 9, France;3. Palaios Association, 86300 Valdivienne, France;1. Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, MRC 121, P.O. Box 37012, Washington, DC 20013-7012, USA;2. Zoological Institute, Russian Academy of Sciences, Universitetskaya nab. 1, 199034 Saint Petersburg, Russia;3. Department of Sedimentary Geology, Geological Faculty, Saint Petersburg State University, 16 Liniya VO 29, 199178 Saint Petersburg, Russia |
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| Abstract: | Choristoderes are a group of extinct diapsid reptiles that once occupied the freshwater systems in the Northern Hemisphere from the Middle Jurassic through the Miocene. The Early Cretaceous monjurosuchid Philydrosaurus from western Liaoning, China, represents a transitional morphotype between a broad-snouted (crocodile-like) and a narrow-snouted (gavial-like) skull during the evolution of Choristodera. New specimens of the taxon from the Early Cretaceous Jiufotang Formation include an incomplete braincase and a nearly complete juvenile skeleton; the study of these specimens provides new information on the braincase and ontogenetic change of the skeleton of this transitional monjurosuchid. In the braincase floor, the foramen internus canalis caroticus externus opens in a groove lateral to the constricted lateral aspect of the parasphenoid, and ventral exposure of this foramen differs from Champsosaurus, in which parasphenoid/pterygoid fusion completely encloses the canal. On the occiput, the vagus nerve foramen penetrates the basioccipital, while the two foramina for the hypoglossal nerve open at the exoccipital/basioccipital suture. Comparative study of the new juvenile specimen with adult Philydrosaurus reveals previously unknown developmental changes of the cranial and postcranial skeleton of this monjurosuchid. Ontogenetically, Philydrosaurus underwent a dramatic change of skull proportions, including elongation of the antorbital and postorbital regions, and elongation of the jaws, with a great increase of the number of marginal teeth. The lower temporal fenestra is entirely closed in early ontogeny, as in large, fully-grown adults. |
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| Keywords: | Anatomy Ontogeny Early Cretaceous Choristodera Western Liaoning China |
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