title: Extreme Ontogenetic Changes in a Ceratosaurian Theropod.
abstract: Ontogenetic variation is documented within many dinosaur species, but extreme ontogenetic changes are rare among dinosaurs, particularly among theropods. Here, we analyze 19 specimens of the Jurassic ceratosaurian theropod Limusaurus inextricabilis, representing six ontogenetic stages based on body size and histological data. Among 78 ontogenetic changes we identify in these specimens, the most unexpected one is the change from fully toothed jaws in the hatchling and juvenile individuals to a completely toothless beaked jaw in the more mature individuals, representing the first fossil record of ontogenetic edentulism among the jawed vertebrates. Jaw morphological data, including those derived from Mi-CT and SR-μCT scanning of Limusaurus specimens, reveal dental alveolar vestiges and indicate that ontogenetic tooth loss in Limusaurus is a gradual, complex process. Our discovery has significant implications for understanding the evolution of the beak, an important feeding structure present in several tetrapod clades, including modern birds. This radical morphological change suggests a dietary shift, probably from omnivory for juvenile Limusaurus to herbivory for adult Limusaurus, which is also supported by additional evidence from gastroliths and stable isotopes. Incorporating new ontogenetic information from Limusaurus into phylogenetic analyses demonstrates surprisingly little effect on its placement when data from different stages are used exclusively, in contrast to previous analyses of tyrannosaurids, but produces subtle differences extending beyond the placement of Limusaurus.
authors.affiliation: Laboratory of Vertebrate Evolution, College of Life Science, Capital Normal University, 105 West 3(rd) Ring Road North, Beijing 100048, China; Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, 142 Xi-Zhi-Men-Wai Street, Beijing 100044, China. Electronic address: uslarky@163.com.
authors.forename: Shuo
authors.initials: S
authors.lastname: Wang
authors.affiliation: Department of Biological Sciences, The George Washington University, Washington, DC 20052, USA.
authors.forename: Josef
authors.initials: J
authors.lastname: Stiegler
authors.affiliation: CNRS UMR 5276, Université Claude Bernard Lyon 1 and Ecole Normale Supérieure de Lyon, Villeurbanne Cedex 69622, France.
authors.forename: Romain
authors.initials: R
authors.lastname: Amiot
authors.affiliation: Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, 19 Bei-Tu-Cheng-Xi Road, Beijing 100029, China.
authors.forename: Xu
authors.initials: X
authors.lastname: Wang
authors.affiliation: Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, 239 Zhangheng Road, Shanghai 201204, China.
authors.forename: Guo-Hao
authors.initials: GH
authors.lastname: Du
authors.affiliation: Department of Biological Sciences, The George Washington University, Washington, DC 20052, USA.
authors.forename: James M
authors.initials: JM
authors.lastname: Clark
authors.affiliation: Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, 142 Xi-Zhi-Men-Wai Street, Beijing 100044, China. Electronic address: xu.xing@ivpp.ac.cn.
authors.forename: Xing
authors.initials: X
authors.lastname: Xu
mesh_terms: D000818:Animals; D005075:Biological Evolution; D049628:Body Size; D001842:Bone and Bones / Q000033:anatomy & histology* / Q000502:physiology; D025061:Dinosaurs / Q000033:anatomy & histology* / Q000502:physiology; D005580:Fossils; D007568:Jaw / Q000033:anatomy & histology* / Q000502:physiology; D010802:Phylogeny; D014070:Tooth / Q000033:anatomy & histology* / Q000502:physiology
keywords: Jurassic; dietary change; ontogenetic edentulism; ontogeny; phylogeny; theropod dinosaur