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[dinosaur] Proganochelys and Proterochersis habitats + longirostry in crocodilians and odontocetes.

Ben Creisler

Recent non-dino papers...

Asher J. Lichtig and Spencer G. Lucas (2017)
A simple method for inferring habitats of extinct turtles.
Palaeoworld (advance online publication)
doi: http://dx.doi.org/10.1016/j.palwor.2017.02.001

We present a simple method of inferring extinct turtle habitats based on four measurements of the shell (two ratios). These ratios are the maximum width of the carapace to the width of the abdominal-femoral sulcus of the plastron, and the ratio of the carapace length to the total height of the shell. Based on an extensive database, extant terrestrial turtles do not have a carapace-width-to-plastron-width ratio that exceeds 1.76. This carapace-width-to-plastron-width ratio in the Triassic turtle Proganochelys is ~2.1, and the length-to-height ratio of Proganochelys is ~2, which suggest an aquatic habitus. Triassic Proterochersis has a carapace-to-plastron-width ratio of 1.89, and a length-to-height ratio of 1.82, which are in the terrestrial range based on discriminant analysis. Inferences based on forelimb proportions and shell bone histology indicate a terrestrial paleoecology for Proganochelys. Conversely, femur morphology and shell cross sections indicate a semi-terrestrial to aquatic paleoecology of Proganochelys. The new method presented here indicates the early turtle Proganochelys was aquatic and Proterochersis was terrestrial in habitus.


M.R. McCurry, C.W. Walmsley, E.M.G. Fitzgerald & C.R. McHenry (2017)
The biomechanical consequences of longirostry in crocodilians and odontocetes.
Journal of Biomechanics (advance online publication)
doi: http://dx.doi.org/10.1016/j.jbiomech.2017.03.003

Unrelated clades of aquatic tetrapod have evolved a similar range of skull shapes, varying from longirostrine (elongate and narrow rostrum) to brevirostrine (short rostrum). However, it is unclear which aspects of organismal performance are associated with this convergence in the range of skull shapes. Furthermore, it is not known how fundamental anatomical differences between groups influence these relationships. Here we address this by examining the load bearing capabilities of the skulls of two of the most diverse groups of living aquatic tetrapod: crocodilians and odontocetes. We use finite element analysis to examine the abilities of different cranial morphologies to resist a range of biologically relevant feeding loads including biting, shaking and twisting. The results allow for form/function relationships to be compared and contrasted between the two groups. We find that cranial shape has similar influences on performance during biting, shaking or twisting load cases at the anterior tooth positions, e.g. brevirostrine species experienced less strain than longirostrine species. The pattern of this form/function relationship is similar for both crocodilians and odontocetes, despite their fundamentally different anatomies. However, when loading teeth at the posterior end or middle of the tooth row the results do not follow the same pattern. Behavioural differences in bite location plays a key role in determining functional abilities in aquatic tetrapod taxa.