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      Palaeoecology of triassic stem turtles sheds new light on turtle origins.

      Proceedings of the Royal Society B: Biological Sciences
      Animals, Body Weights and Measures, Environment, Forelimb, anatomy & histology, Fossils, Fresh Water, Phylogeny, Turtles, physiology

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          Abstract

          Competing hypotheses of early turtle evolution contrast sharply in implying very different ecological settings-aquatic versus terrestrial-for the origin of turtles. We investigate the palaeoecology of extinct turtles by first demonstrating that the forelimbs of extant turtles faithfully reflect habitat preferences, with short-handed turtles being terrestrial and long-handed turtles being aquatic. We apply this metric to the two successive outgroups to all living turtles with forelimbs preserved, Proganochelys quenstedti and Palaeochersis talampayensis, to discover that these earliest turtle outgroups were decidedly terrestrial. We then plot the observed distribution of aquatic versus terrestrial habits among living turtles onto their hypothesized phylogenies. Both lines of evidence indicate that although the common ancestor of all living turtles was aquatic, the earliest turtles clearly lived in a terrestrial environment. Additional anatomical and sedimentological evidence favours these conclusions. The freshwater aquatic habitat preference so characteristic of living turtles cannot, consequently, be taken as positive evidence for an aquatic origin of turtles, but must rather be considered a convergence relative to other aquatic amniotes, including the marine sauropterygians to which turtles have sometimes been allied.

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          Author and article information

          Journal
          15002764
          1691562
          10.1098/rspb.2003.2523

          Chemistry
          Animals,Body Weights and Measures,Environment,Forelimb,anatomy & histology,Fossils,Fresh Water,Phylogeny,Turtles,physiology

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