Palaeoneurology of the early cretaceous iguanodont Proa valdearinnoensis and its bearing on the parallel developments of cognitive abilities in theropod and ornithopod dinosaurs

Abstract

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 (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 analyzed. 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 encephalization of P. valdearinnoensis through the calculation of the encephalization 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 P. valdearinnoensis (3.611) suggests that this species was significantly more encephalized than most if not all extant nonavian, nonmammalian amniotes. Our work adds to the growing body of data concerning theoretical cognitive capabilities in dinosaurs and supports the idea that an increasing encephalization was fostered not only in theropods but also in parallel in the shorter‐lived lineage of ornithopods. P. 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 favored a degree of encephalization that was outstanding by reptile standards.

Could theropod dinosaurs have evolved to a human level of intelligence?

“…Analysis of brain size relative to body size reinforces the conclusion from paleontological behavioral data that at least some dinosaur species rivaled living birds and mammals in behavioral sophistication (Balanoff et al, 2013;Hopson, 1977;Jerison, 1973;Knoll et al, 2021;Ksepa et al, 2020;Russell & Seguin, 1982). For example, although brain size-body size ratios for many dinosaur species tend to be within the range of extant reptiles, many of the theropod dinosaurs show ratios greater than those for living reptiles (for example, allosaurids and tyrannosaurids), and maniraptorid theropod dinosaurs show brainbody ratios that approach those of birds (Figure 2) (Hopson, 1977;Jerison, 1973;Ksepa et al, 2020).…”

Neurovascular anatomy of dwarf dinosaur implies precociality in sauropods

“…As is generally the case in non-maniraptoriform dinosaurs (e.g., Witmer and Ridgely, 2008a ; Witmer and Ridgely, 2009 ; Knoll et al, 2015 ; Knoll et al, 2021 ), many characteristics of the mid- and hindbrain are not perceivable with certainty (however, see Evans, 2005 ; Morhardt, 2016 ; Fabbri et al, 2017 ) on the braincase endocast of DFMMh/FV 581.1 ( Figure 1A ), which implies scarce correlation of the actual brain and the inner surface of the endocranial cavity (see Watanabe et al, 2019 , for ontogenetic variations in recent archosaurs).…”

Theropod dinosaurs had primate‐like numbers of telencephalic neurons

“…As modeling techniques based on micro‐CT data improve and allow the volume of other brain structures to be estimated (Knoll et al., 2021), more evidence should help distinguish which dinosaur and pterosaur species were ecto‐ or endothermic. The cerebellum, for example, is decidedly larger in extant endothermic species compared to ectothermic species of similar body mass (Kverkova et al., 2022); thus, the size of the cerebellum relative to the mass of the telencephalon (Herculano‐Houzel, 2022) and of the body may serve as a new diagnostic criterion to infer the metabolic status of species of the prehistoric fauna.…”