Chapter

Early Evolutionary History of the Synapsida

Part of the series Vertebrate Paleobiology and Paleoanthropology pp 25-51

Date:

Was Ophiacodon (Synapsida, Eupelycosauria) a Swimmer? A Test Using Vertebral Dimensions

  • Ryan N. FeliceAffiliated withDepartment of Biological Sciences, Ohio University Email author 
  • , Kenneth D. AngielczykAffiliated withDepartment of Geology, Field Museum of Natural History

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Abstract

Ophiacodon, a Permian synapsid, has been hypothesized to be semi-aquatic. This interpretation is based on a range of evidence, including observations of histology, phalangeal morphology, dentition, and taphonomy. However, many of these data are inconclusive or have been reinterpreted. Here we investigate whether the morphology of the axial skeleton in Ophiacodon displays specializations for aquatic locomotion. Qualitative and quantitative comparisons of Ophiacodon to extant terrestrial and semi-aquatic tetrapods demonstrate that the distribution of centrum lengths in its vertebral column is similar in some ways to those of extant semi-aquatic reptiles. However, other basal synapsids that are widely regarded as terrestrial show comparable patterns, and the correlation between swimming style and vertebral morphology in extant semi-aquatic tetrapods may be weaker than previously thought. Therefore, vertebral proportions provide little support for a semi-aquatic lifestyle in Ophiacodon. Given that most lines of evidence are equivocal at best, we suggest that future studies that consider the ecology of Ophiacodon use a terrestrial lifestyle as a null hypothesis.

Keywords

Permian Carboniferous Centrum length Limb length Aquatic tetrapods Ophiacodontidae