A Jurassic ceratosaur from China helps clarify avian digital homologies

Xing Xu (), James M. Clark, Jinyou Mo, Jonah Choiniere, Catherine A. Forster, Gregory M. Erickson, David W. E. Hone, Corwin Sullivan, David A. Eberth, Sterling Nesbitt, Qi Zhao, Rene Hernandez, Cheng-kai Jia, Feng-lu Han and Yu Guo
Additional contact information
Xing Xu: Institute of Vertebrate Paleontology and Paleoanthropology
James M. Clark: George Washington University
Jinyou Mo: Natural History Museum of Guangxi, Nanning, Guangxi 530012, China
Jonah Choiniere: George Washington University
Catherine A. Forster: George Washington University
Gregory M. Erickson: Florida State University, Tallahassee, Florida 32306, USA
David W. E. Hone: Institute of Vertebrate Paleontology and Paleoanthropology
Corwin Sullivan: Institute of Vertebrate Paleontology and Paleoanthropology
David A. Eberth: Royal Tyrrell Museum, Drumheller, Alberta T0J 0Y0, Canada
Sterling Nesbitt: American Museum of Natural History, Central Park West at 79th Street, New York, New York 10024, USA
Qi Zhao: Institute of Vertebrate Paleontology and Paleoanthropology
Rene Hernandez: Instituto de Geologia, Universidad Nacional Autónoma de México, Ciudad Universitaria, Del. Coyocan, México DF 04510, Mexico
Cheng-kai Jia: Research Institute of Exploration and Development, Xinjiang Oilfield Company, Karamay, Xinjiang 834000, China
Feng-lu Han: Institute of Vertebrate Paleontology and Paleoanthropology
Yu Guo: Institute of Vertebrate Paleontology and Paleoanthropology

Nature, 2009, vol. 459, issue 7249, 940-944

Abstract: Abstract Theropods have traditionally been assumed to have lost manual digits from the lateral side inward, which differs from the bilateral reduction pattern seen in other tetrapod groups. This unusual reduction pattern is clearly present in basal theropods, and has also been inferred in non-avian tetanurans based on identification of their three digits as the medial ones of the hand (I-II-III). This contradicts the many developmental studies indicating II-III-IV identities for the three manual digits of the only extant tetanurans, the birds. Here we report a new basal ceratosaur from the Oxfordian stage of the Jurassic period of China (156–161 million years ago), representing the first known Asian ceratosaur and the only known beaked, herbivorous Jurassic theropod. Most significantly, this taxon possesses a strongly reduced manual digit I, documenting a complex pattern of digital reduction within the Theropoda. Comparisons among theropod hands show that the three manual digits of basal tetanurans are similar in many metacarpal features to digits II-III-IV, but in phalangeal features to digits I-II-III, of more basal theropods. Given II-III-IV identities in avians, the simplest interpretation is that these identities were shared by all tetanurans. The transition to tetanurans involved complex changes in the hand including a shift in digit identities, with ceratosaurs displaying an intermediate condition.

Date: 2009
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DOI: 10.1038/nature08124

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