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Stenopterygius (Ichthyosauria) forelimb/hind limb morphological integration



From: Ben Creisler
bcreisler@gmail.com

A paper in the new issue of Paleobiology:


Erin E. Maxwell and T. Alexander Dececchi (2013)
Ontogenetic and stratigraphic influence on observed phenotypic
integration in the limb skeleton of a fossil tetrapod.
Paleobiology 39(1):123-134
http://www.bioone.org/doi/abs/10.1666/0094-8373-39.1.123


Understanding morphological integration is one of the central goals of
evolutionary developmental biology. Despite its applicability to
questions of paleontological interest, there are few studies on
integration in fossil vertebrates. In this study, we examine limb
integration in the Lower Jurassic ichthyosaur Stenopterygius
quadriscissus, with the aim of examining the effect of ontogeny and
anagenetic changes over short geological time spans on metrics of limb
integration. Both ontogenetic and stratigraphic effects had a
significant influence on measured values of integration, the identity
of strongly integrated elements, and some common ratio values such as
the relative integration of the forelimb to the hind limb, or
within-limb to between-limb integration. Ontogenetic effects were
relatively greater, although this could be linked to sample size.
Although adults showed the lowest levels of overall integration, they
possessed high levels of integration between serially homologous
elements, something that was unexpected due to strong divergence in
limb size and perhaps functional differences in derived ichthyosaurs.
Ontogenetic differences in the relative integration of the forelimb to
the hind limb are probably related to early locomotor demands on the
forelimb. We conclude that if samples are pooled, the resulting
pattern of integration may not reflect any one subsample but will be a
composite created through the superposition of several variables.
Pooling data in paleontological studies of integration has a
non-trivial effect on the results obtained.


Supplementary materials deposited at Dryad: doi:10.5061/dryad.pm130