Please use this identifier to cite or link to this item: https://hdl.handle.net/2440/86448
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Type: Journal article
Title: Locomotory capabilities in the Early Cretaceous ichthyosaur Platypterygius australis based on osteological comparisons with extant marine mammals
Author: Zammit, M.
Kear, B.
Norris, R.
Citation: Geological Magazine, 2014; 151(1):87-99
Publisher: Cambridge University Press
Issue Date: 2014
ISSN: 0016-7568
1469-5081
Statement of
Responsibility: 
Maria Zammit, Benjamin P. Kear and Rachel M. Norris
Abstract: 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.
Keywords: Ichthyosauria; Platypterygius ; comparative anatomy; marine mammals; Cretaceous
Description: Published online: 01 November 2013
Rights: © Cambridge University Press 2013
DOI: 10.1017/S0016756813000782
Grant ID: ARC
Appears in Collections:Animal and Veterinary Sciences publications
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