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Shell geometry and habitat determination in extinct and extant turtles (Reptilia: Testudinata)

Published online by Cambridge University Press:  08 April 2016

Roger B. J. Benson
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, United Kingdom. E-mail:
Gábor Domokos
Department of Mechanics, Materials and Structures, Budapest University of Technology and Economics, H-1111 Budapest, Mùgyetem rkp 3, K242, Hungary
Péter L. Várkonyi
Department of Mechanics, Materials and Structures, Budapest University of Technology and Economics, H-1111 Budapest, Mùgyetem rkp 3, K242, Hungary
Robert R. Reisz
Department of Biology, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, Ontario L5L 1C6, Canada
E-mail address:


A variety of means, including forelimb proportions and shell bone histology have been used to infer the paleoecology of extinct turtles. However, the height-to-width ratio of the shell (as a one-parameter shell model) has been dismissed because of its unreliability, and more complex aspects of shell geometry have generally been overlooked. Here we use a more reliable, three-parameter geometric model of the shell outline in anterior view as a means to assess turtle paleoecology. The accuracy of predictions of extant turtle ecology based on our three-parameter shell model is comparable to that derived from forelimb proportions when distinguishing between three ecological classes (terrestrial, semiaquatic, and aquatic). Higher accuracy is obtained when distinguishing between two classes (terrestrial and non-terrestrial), because the contours of aquatic and semiaquatic turtles are often very similar. Our model classifies Proterochersis robusta, a stem turtle from the Late Triassic of Germany, as non-terrestrial, and likely semiaquatic. Our method, combined with inferences based on limb proportions, indicates a diverse range of ecotypes represented by Late Triassic stem turtles. This implies that the ecological diversification of stem-group turtles may have been rapid, or that a substantial period of currently cryptic diversification preceded the first fossil appearance of the turtle stem lineage during the Late Triassic.

Copyright © The Paleontological Society 

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