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Locomotory capabilities in the Early Cretaceous ichthyosaur Platypterygius australis based on osteological comparisons with extant marine mammals
- MARIA ZAMMIT, BENJAMIN P. KEAR, RACHEL M. NORRIS
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- Journal:
- Geological Magazine / Volume 151 / Issue 1 / January 2014
- Published online by Cambridge University Press:
- 01 November 2013, pp. 87-99
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- Article
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Reconstructing the swimming capabilities of extinct marine tetrapods is critical for unravelling broader questions about their palaeobiology, palaeoecology and palaeobiogeography. Ichthyosaurs have long been the subject of such investigations because, alongside cetaceans, they are one of the few tetrapod lineages to achieve a highly specialized fish-like body plan. The dominant locomotory mode for the majority of derived, post-Triassic ichthyosaurs is hypothesized to have been caudal fin-driven propulsion. Limb-based swimming has however been suggested for some highly autapomorphic forms, such as the Cretaceous genus Platypterygius, which has a remarkably robust humeral morphology and exceptionally broad paddle-like limbs. To evaluate this atypical lifestyle model, we conducted a comprehensive comparative osteological assessment of Platypterygius in relation to extant marine mammals, whose analogous skeletal frameworks provide a structurally compatible selection of alternate propulsive strategies. Based on a proxy exemplar of the most completely known species, P. australis from the Early Cretaceous of Australia, the propodial shape, absence of functional elbow/knee joints, tightly interlocking carpals, hyperphalangy and extreme reduction of the pelvic girdle are most similar to cetaceans as opposed to pinnipeds or dugongs. There is no obvious structural consistency with aquatic mammals that use sustained forelimb-driven swimming. The exceptionally broad fore-paddle (a product of hyperdactyly) and extensive humeral muscle insertions might therefore have had a cetacean-like role in enhancing manoeuvrability and acceleration performance. We conclude that, despite its atypical features, P. australis was most likely similar to other ichthyosaurs in using lateral sweeps of the tailfin to generate primary propulsive thrust.
Contributors
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- By Jennifer Alvarez, Ananda B. Amstadter, Metin Başoğlu, David M. Benedek, Charles C. Benight, George A. Bonanno, Evelyn J. Bromet, Richard A. Bryant, Barbara Lopes Cardozo, M. L. Somchai Chakkraband, Claude Chemtob, Roman Cieslak, Lauren M. Conoscenti, Joan M. Cook, Judith Cukor, Carla Kmett Danielson, JoAnn Difede, Charles DiMaggio, Anja J.E. Dirkzwager, Cristiane S. Duarte, Jon D. Elhai, Diane L. Elmore, Yael L.E. Errera, Julian D. Ford, Carol S. Fullerton, Sandro Galea, Freya Goodhew, Neil Greenberg, Lindsay Greene, Linda Grievink, Michael J. Gruber, Sumati Gupta, Johan M. Havenaar, Alesia O. Hawkins, Clare Henn-Haase, Kimberly Eaton Hoagwood, Christina W. Hoven, Sabra S. Inslicht, Krzysztof Kaniasty, Ronald C. Kessler, Rachel Kimerling, Richard V. King, Rolf J. Kleber, Jessica Mass Levitt, Brett T. Litz, Maria Livanou, Katelyn P. Mack, Paula Madrid, Shira Maguen, Paul Maguire, Donald J. Mandell, Charles R. Marmar, Andrea R. Maxwell, Shannon E. McCaslin, Alexander C. McFarlane, Thomas J. Metzler, Summer Nelson, Yuval Neria, Elana Newman, Thomas C. Neylan, Fran H. Norris, Carol S. North, Lawrence A. Palinkas, Benjaporn Panyayong, Maria Petukhova, Betty Pfefferbaum, Marleen Radigan, Beverley Raphael, James Rodriguez, G. James Rubin, Kenneth J. Ruggiero, Ebru Şalcıoğlu, Nancy A. Sampson, Arieh Y. Shalev, Bruce Shapiro, Laura M. Stough, Prawate Tantipiwatanaskul, Warunee Thienkrua, Phebe Tucker, J. Blake Turner, Robert J. Ursano, Bellis van den Berg, Peter G. van der Velden, Frits van Griensven, Miranda Van Hooff, Edward Waldrep, Philip S. Wang, Simon Wessely, Leslie H. Wind, C. Joris Yzermans, Heidi M. Zinzow
- Edited by Yuval Neria, Columbia University, New York, Sandro Galea, University of Michigan, Ann Arbor, Fran H. Norris
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- Book:
- Mental Health and Disasters
- Published online:
- 07 May 2010
- Print publication:
- 20 July 2009, pp xi-xvi
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