Platypterygius (Ichthyosauria) fetal remains from Australia

[Ben Creisler <bcreisler@gmail.com>]

From: Ben Creisler
bcreisler@gmail.com


A new online paper:


Benjamin P. Kear and Maria Zammit (2013)
In utero foetal remains of the Cretaceous ichthyosaurian
Platypterygius: ontogenetic implications for character state efficacy.
Geological Magazine (advance online publication)
DOI: http://dx.doi.org/10.1017/S0016756813000113
http://128.232.233.5/action/displayAbstract?fromPage=online&aid=8911886&fulltextType=RA&fileId=S0016756813000113



Ichthyosaurians provide some of the most famous examples of ‘live
birth’ in the amniote fossil record based on spectacular complete
skeletons of gravid females. Such remains facilitate direct
comparisons between adult and foetal life stages, and thus have
significant impact on phylogenetic hypotheses that require discrete
character states to be ontogenetically uncoupled. This is especially
true for Cretaceous ichthyosaurian taxa, the majority of which have
been established using single specimens of assumed osteological
maturity. Our assessment of in utero ichthyosaurian remains from the
late Albian of Australia was therefore aimed at testing ontogenetic
stability amongst key traits defining the most ubiquitous Cretaceous
taxon: Platypterygius. Surprisingly, almost all of the salient
features were identifiable in our sample of undoubtedly immature
individuals. Indeed, only the proportions of the sclerotic ring,
relative ossification and fusion of various basicranial elements,
development of the axial skeleton, prominence of the deltopectoral
crest and dorsal trochanter, and formation (but seemingly not number)
of distal articular facets on the humerus were found to vary from
larger-bodied members of the same species (P. australis). Ontogenetic
continuity amongst the majority of other phylogenetically pertinent
skeletal structures advocates their application for cladistic
analyses, and suggests that many classic characters used to
differentiate Platypterygius remain diagnostic irrespective of growth
stage.