CT data and 3D models associated with: Palaeoneurology of the Early Cretaceous iguanodont Proa valdearinnoensis and its bearing on the parallel developments of cognitive abilities in theropod and ornithopod dinosaurs

Proa valdearinnoensis is a relatively large-headed and stocky
iguanodontian dinosaur from the latest Early Cretaceous of Spain. Its
braincase is known from three specimens. Similar to that of other
dinosaurs, it shows a mosaic ossification pattern in which most of the
bones seem to have fused together indistinguishably while a few bones
(frontoparietal, basioccipital) might have remained loosely attached. The
endocasts of the three specimens are described based on CT data and
digital reconstructions. They show unmistakable morphological similarities
with the endocast of closely related taxa, such as Sirindhorna khoratensis
(which is close in age but from Thailand). This supports a high
conservatism of the endocranial cavity. The issue of volumetric
correspondence between endocranial cavity and brain in dinosaurs is
analysed. Although a brain-to-endocranial cavity (BEC) index of 0.50 has
been traditionally used, we employ instead  0.73. This is indeed
the mid-value between the situation in adults of Alligator
mississippiensis and Gallus gallus, which are members of the extant
bracketing taxa of dinosaurs (Crocodilia and Aves). We thence gauge the
level of encephalisation of Proa valdearinnoensis by the calculation of
the Encephalisation Quotient (EQ), which remains valuable as a metric for
assessing the degree of cognitive function in extinct taxa, especially
those with fully ossified braincases like dinosaurs and other archosaurs.
The EQ obtained for Proa valdearinnoensis (3.611) suggests that this
species was significantly more encephalised than most if not all extant
non-avian, non-mammalian amniotes. Our work adds to the growing body of
data concerning theoretical cognitive capabilities in dinosaurs and
supports the idea that increasing encephalisations were fostered not only
once in theropods but also in parallel in the shorter-lived lineage of
ornithopods. Proa valdearinnoensis was ill-equipped to respond to theropod
dinosaurs and possibly lived in groups as a strategy to mitigate the risk
of being predated upon. We hypothesize that group-living and protracted
caring of juveniles in this and possibly many other iguanodontian
ornithopods favoured a degree of encephalisation that was outstanding by
reptile standards.