The skull roof tracks the brain during the evolution and development of reptiles including birds

Abstract

Major transformations in brain size and proportions, such as the enlargement of the brain during the evolution of birds, are accompanied by profound modifications to the skull roof. However, the hypothesis of concerted evolution of shape between brain and skull roof over major phylogenetic transitions, and in particular of an ontogenetic relationship between specific regions of the brain and the skull roof, has never been formally tested. We performed 3D morphometric analyses to examine the deep history of brain and skull-roof morphology in Reptilia, focusing on changes during the well-documented transition from early reptiles through archosauromorphs, including nonavian dinosaurs, to birds. Non-avialan taxa cluster tightly together in morphospace, whereas Archaeopteryx and crown birds occupy a separate region. There is a one-to-one correspondence between the forebrain and frontal bone and the midbrain and parietal bone. Furthermore, the position of the forebrain-midbrain boundary correlates significantly with the position of the frontoparietal suture across the phylogenetic breadth of Reptilia and during the ontogeny of individual taxa. Conservation of position and identity in the skull roof is apparent, and there is no support for previous hypotheses that the avian parietal is a transformed postparietal. The correlation and apparent developmental link between regions of the brain and bony skull elements are likely to be ancestral to Tetrapoda and may be fundamental to all of Osteichthyes, coeval with the origin of the dermatocranium.

Modularity and evolution of flower shape: the role of function, development, and spandrels inErica

“…From the bacterial flagellum (McAdams et al, 2004) to the skull shape of dinosaurs (Fabbri et al, 2017), modular organization pervades life's phenotypes (Wagner et al, 2007).…”

Endocranial anatomy and life habits of the Early Triassic archosauriformProterosuchus fergusi

“…; Balanoff & Bever ; Fabbri et al . ). Perhaps with further research, the correlations between form and function of the endocranial anatomy will become better understood and explain some of the similarities between relatively phylogenetically‐distant taxa that our study displays.…”

“…Trotteyn & Paulina‐Carabajal () reconstructed the endocranium of the proterochampsian Tropidosuchus romeri , while Fabbri et al . () reconstructed the endocranium of P. fergusi (RC 846; although Fabbri et al . incorrectly identified the specimen as ‘RC 96’ which actually corresponds to a dicynodont; Ezcurra ) and E. capensis .…”

“…However, the endocasts from Fabbri et al . () are incompletely figured and not described in the text, and are therefore largely uninformative in regard to the morphology of the early archosauriform brain cavity.…”

The Endocranial Cavity of Oviraptorosaur Dinosaurs and the Increasingly Complex, Deep History of the Avian Brain

“…If correctly interpreted, this would call into question a generalized assumption that the functional significance of the brain and its regions gives it structural primacy over the surrounding head tissues. The complex signaling relationship between the brain and cranial mesenchyme is only beginning to be meaningfully outlined [Marcucio et al, 2011;Fabbri et al, 2017], and we are hopeful that the fossil record will serve as an increasingly useful resource in assessing the phenotypic potential of these integrated systems.…”