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Arenysaurus (hadrosaur from Spain) neuroanatomy

Ben Creisler

An online preprint version of a new paper in open access:

Penélope Cruzado-Caballero, Josep Fortuny, Sergio Llacer & José
Ignacio JI Canudo (2014)
Arenysaurus ardevoli, first paleoneuroanatomical description of a
European hadrosaurid.
PeerJ PrePrints 2:e590v1
doi:  http://dx.doi.org/10.7287/peerj.preprints.590v1

The neuroanatomy of hadrosaurid dinosaurs is well known from North
America and Asia. In Europe only a few cranial remains have been
recovered with the braincase. Arenysaurus is the first European
endocast for which the paleoneuroanatomy has been studied. The
resulting data have enabled us to draw ontogenetic, phylogenetic and
functional inferences. Arenysaurus preserves the endocast and the
inner ear. This cranial material was CT-scanned, and a 3D-model was
generated. The endocast morphology supports a general pattern for
hadrosaurids with some characters that distinguish to a subfamily
level, such as a brain cavity anteroposteriorly shorter or the angle
of the major axis of the cerebral hemisphere to the horizontal in
lambeosaurines. Both characters are present in the endocast of
Arenysaurus. Moreover, osteological features indicate an adult
ontogenetic stage while some paleoneuroanatomical features are
indicative of a subadult ontogenetic stage and even a juvenile
ontogenetic stage. Finally, a comparison with other hadrosaurids
reveals that the low values for the angle of the dural peak may be an
autapomorphy exclusive to the Parasaurolophus genus. It is
hypothesized that the presence of puzzling characters that suggest
different ontogenetic stages for this specimen, may reflect some
degree of dwarfism in Arenysaurus. Regarding the inner ear, its
structure shows differences from the ornithopod clade with respect to
the height of the semicircular canals. These differences could lead to
a decrease in the compensatory movements of eyes and head, with
important implications for the paleobiology and behavior of
hadrosaurid taxa such as Edmontosaurus, Parasaurolophus and
Arenysaurus. These differences in the vestibular system could be used
as a phylogenetical signal. The endocranial morphology of European
hadrosaurids sheds new light on the evolution of this group and may
reflect the conditions in the archipelago where these animals lived
during the Late Cretaceous.