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Pararcus, new placodont from the Netherlands



From: Ben Creisler
bcreisler@gmail.com


A new online paper describing Pararcus diepenbroeki, a new placodont:


Nicole Klein and Torsten M. Scheyer (2013)
A new placodont sauropterygian from the Middle Triassic of the Netherlands.
Acta Palaeontologica Polonica (in press)
doi: http://dx.doi.org/10.4202/app.2012.0147
http://app.pan.pl/article/item/app20120147.html


A new genus and species of a non-cyamodontoid placodont is described
on the basis of an incomplete and disarticulated skeleton from
Winterswijk, The Netherlands, dated as early Anisian (Lower
Muschelkalk). The new taxon is unique in a ventrolateral expansion of
the neural arches of the posterior presacral and sacral vertebrae, in
which the transverse process is incorporated. It has a round,
plate-like pubis and ischium, and the only preserved long bone
indicates elongated limbs. The holotype, which is relatively large (>
1.35 m) for a basal sauropterygian, has still un-fused halves of
neural arches and no distinct neural spine developed yet. The new
taxon is assigned to non-cyamodontoid placodonts based on its round
girdle elements, the morphology of dorsal-, sacral-, and caudal ribs,
the straight medial and mediolateral elements of gastral ribs, and the
presence of un-sutured armour plates. In spite of the large size of
the holotype, there is evidence that the animal was not yet fully
grown, based on the paired neural arches, and general poor
ossification of the bones. The un-fused halves of neural arches are
interpreted as skeletal paedomorphosis, which is typical for
vertebrates with a secondary marine life style. The sacral region
seems to be highly flexible.