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Crocodylomorph vertebral column aquatic adaptation (free pdf)

Ben Creisler

A new paper in open access:

Julia L. Molnar, Stephanie E. Pierce, Bhart-Anjan S. Bhullar, Alan H.
Turner & John R. Hutchinson (2015)
Morphological and functional changes in the vertebral column with
increasing aquatic adaptation in crocodylomorphs.
Royal Society Open Science 2: 150439
DOI: 10.1098/rsos.150439

The lineage leading to modern Crocodylia has undergone dramatic
evolutionary changes in morphology, ecology and locomotion over the
past 200+ Myr. These functional innovations may be explained in part
by morphological changes in the axial skeleton, which is an integral
part of the vertebrate locomotor system. Our objective was to estimate
changes in osteological range of motion (RoM) and intervertebral joint
stiffness of thoracic and lumbar vertebrae with increasing aquatic
adaptation in crocodylomorphs. Using three-dimensional virtual models
and morphometrics, we compared the modern crocodile Crocodylus to five
extinct crocodylomorphs: Terrestrisuchus, Protosuchus, Pelagosaurus,
Steneosaurus and Metriorhynchus, which span the spectrum from
terrestrial to fully aquatic. In Crocodylus, we also experimentally
measured changes in trunk flexibility with sequential removal of
osteoderms and soft tissues. Our results for the more aquatic species
matched our predictions fairly well, but those for the more
terrestrial early crocodylomorphs did not. A likely explanation for
this lack of correspondence is the influence of other axial
structures, particularly the rigid series of dorsal osteoderms in
early crocodylomorphs. The most important structures for determining
RoM and stiffness of the trunk in Crocodylus were different in
dorsoventral versus mediolateral bending, suggesting that changes in
osteoderm and rib morphology over crocodylomorph evolution would have
affected movements in some directions more than others.



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