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Spinosaurus is not an aquatic dinosaur

View ORCID ProfilePaul C. Sereno, View ORCID ProfileNathan Myhrvold, Donald M. Henderson, Frank E. Fish, Daniel Vidal, View ORCID ProfileStephanie L. Baumgart, Tyler M. Keillor, Kiersten K. Formoso, Lauren L. Conroy
doi: https://doi.org/10.1101/2022.05.25.493395
Paul C. Sereno
1Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL 60637
2Committee on Evolutionary Biology, University of Chicago, IL 60637
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  • For correspondence: dinosaur@uchicago.edu
Nathan Myhrvold
3Intellectual Ventures, 3150 139th Avenue Southeast, Bellevue, WA 98005
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Donald M. Henderson
4Royal Tyrrell Museum of Palaeontology, Drumheller, Alberta, Canada, TOJ OY
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Frank E. Fish
5Department of Biology, West Chester University, West Chester, PA 19383
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Daniel Vidal
6Grupo de Biología Evolutiva, UNED, 28040 Madrid, Spain
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Stephanie L. Baumgart
1Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL 60637
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Tyler M. Keillor
1Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL 60637
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Kiersten K. Formoso
7Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089
8Dinosaur Institute, Natural History Museum of Los Angeles County, Los Angeles, CA 90007
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Lauren L. Conroy
1Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL 60637
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Abstract

A predominantly fish-eating diet was envisioned for the sail-backed theropod dinosaur, Spinosaurus aegyptiacus, when its elongate jaws with subconical teeth were unearthed a century ago in Egypt. Recent discovery of the high-spined tail of that skeleton, however, led to a bolder conjecture, that S. aegyptiacus was the first fully aquatic dinosaur. The ‘aquatic hypothesis’ posits that S. aegyptiacus was a slow quadruped on land but a capable pursuit predator in coastal waters, powered by an expanded tail. We test these functional claims with skeletal and flesh models of S. aegyptiacus. We assembled a CT-based skeletal reconstruction based on the fossils, to which we added internal air and muscle to create a posable flesh model. That model shows that on land S. aegyptiacus was bipedal and in deep water was an unstable, slow surface swimmer (<1m/s) too buoyant to dive. Living reptiles with similar spine-supported sails over trunk and tail in living reptiles are used for display rather than aquatic propulsion, and nearly all extant secondary swimmers have reduced limbs and fleshy tail flukes. New fossils also show that Spinosaurus ranged far inland. Two stages are clarified in the evolution of Spinosaurus, which is best understood as a semiaquatic bipedal ambush piscivore that frequented the margins of coastal and inland waterways.

Competing Interest Statement

The authors have declared no competing interest.

Copyright 
The copyright holder for this preprint is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY 4.0 International license.
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Posted May 26, 2022.
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Spinosaurus is not an aquatic dinosaur
Paul C. Sereno, Nathan Myhrvold, Donald M. Henderson, Frank E. Fish, Daniel Vidal, Stephanie L. Baumgart, Tyler M. Keillor, Kiersten K. Formoso, Lauren L. Conroy
bioRxiv 2022.05.25.493395; doi: https://doi.org/10.1101/2022.05.25.493395
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Spinosaurus is not an aquatic dinosaur
Paul C. Sereno, Nathan Myhrvold, Donald M. Henderson, Frank E. Fish, Daniel Vidal, Stephanie L. Baumgart, Tyler M. Keillor, Kiersten K. Formoso, Lauren L. Conroy
bioRxiv 2022.05.25.493395; doi: https://doi.org/10.1101/2022.05.25.493395

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