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A crocodylian-style cloaca in a non-avialan dinosaur

View ORCID ProfilePhil R. Bell, View ORCID ProfileMichael Pittman, View ORCID ProfileThomas G. Kaye, View ORCID ProfileChristophe Hendrickx
doi: https://doi.org/10.1101/2020.10.11.335398
Phil R. Bell
1School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia; email:
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  • For correspondence: pbell23@une.edu.au pbell23@une.edu.au
Michael Pittman
2Vertebrate Palaeontology Laboratory, Division of Earth and Planetary Science, The University of Hong Kong, Pokfulam, Hong Kong SAR, China; email:
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  • For correspondence: pbell23@une.edu.au mpittman@hku.hk
Thomas G. Kaye
3Foundation for Scientific Advancement, Sierra Vista, Arizona, USA; email:
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  • For correspondence: tom@tomkaye.com
Christophe Hendrickx
4Unidad Ejecutora Lillo, CONICET-Fundación Miguel Lillo, Miguel Lillo 251, San Miguel de Tucumán 4000, Tucumán, Argentina; email:
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  • For correspondence: christophendrickx@gmail.com
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Abstract

Our knowledge of the reproductive biology of dinosaurs covers a range of aspects, from brooding behaviour to nesting style and the timing of sexual maturity. Yet, the basic anatomy and function of the cloaca in non-avialan dinosaurs remains unknown. Here, we describe the outer morphology of the only known non-avialan dinosaur cloaca, preserved in an exceptional specimen of the early-diverging ceratopsian dinosaur Psittacosaurus. We clarify the position of the cloaca with respect to the ischia and caudal vertebrae and document the scales immediately adjacent to the abdomen and tail. We find that the cloaca is from a near-sexually mature subadult individual and is most similar to the cloaca of crocodylians, to the exclusion of lepidosaurians and birds. However, the sex of SMF R 4970 could not be determined as the cloaca and the rest of the specimen does not yield any sexually dimorphic information. This study highlights the ongoing role of exceptional specimens in providing rare soft tissues that help to bridge longstanding gaps in our knowledge of the basic biology of dinosaurs and other extinct reptiles.

Competing Interest Statement

The authors have declared no competing interest.

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The copyright holder for this preprint is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. All rights reserved. No reuse allowed without permission.
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Posted October 12, 2020.
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A crocodylian-style cloaca in a non-avialan dinosaur
Phil R. Bell, Michael Pittman, Thomas G. Kaye, Christophe Hendrickx
bioRxiv 2020.10.11.335398; doi: https://doi.org/10.1101/2020.10.11.335398
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A crocodylian-style cloaca in a non-avialan dinosaur
Phil R. Bell, Michael Pittman, Thomas G. Kaye, Christophe Hendrickx
bioRxiv 2020.10.11.335398; doi: https://doi.org/10.1101/2020.10.11.335398

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