Avian brain evolution: new data from Palaeogene birds (Lower Eocene) from England

Abstract

Investigation of how the avian brain evolved to its present state is informative for studies of the theropod-bird transition, and as a parallel to mammalian brain evolution. Neurological anatomy in fossil bird species can be inferred from endocranial casts, but such endocasts are rare. Here, we use computed tomographic analysis to determine the state of brain anatomy in two marine birds from the Lower Eocene London Clay Formation of England. The brains of Odontopteryx (Odontopterygiformes) and Prophaethon (Pelecaniformes) are remarkably similar to those of extant seabirds, and probably possessed similar somatosensory and motor capabilities. Each virtual endocast exhibits a degree of telencephalic expansion comparable to living avian species. However, the eminentia sagittalis (wulst), a feature characteristic of all living birds, is poorly developed. Our findings support the conclusion that much of the telencephalic expansion of modern birds was complete by the end of the Mesozoic, but that overall telencephalic volume has increased throughout the Cenozoic through dorsal expansion of the eminentia sagittalis. We suggest that improvements in cognition relating to telencephalic expansion may have provided neornithine avian clades with an advantage over archaic lineages at the Cretaceous-Tertiary boundary, explaining their survival and rapid diversification in the Cenozoic.

Flight performance of the largest volant bird

“…The pseudoteeth exhibit a bilaterally symmetrical size progression, with the first two large pseudoteeth separated by two smaller pseudoteeth and the number of intervening small pseudoteeth increasing to three in the caudal part of the jaw. Impressions of the cerebral hemispheres indicate that the sagittal eminence was strongly projected and extended to near the rostral margin of the cerebral hemisphere, which is in contrast to the poorly developed sagittal eminence reported in the Early Eocene pelagornithid Odontopteryx (24). The mandibular ramus is separated into two sections by a complex intraramal joint.…”

Pseudotoothed Birds (Aves, Odontopterygiformes) from the Early Tertiary of Morocco

“…This crest is homologous to the crista fossae parabasalis. Milner and Walsh (2009) stated that the divergence of the nervus glossopharyngeus and nervus vagus is close to the exit of the latter, and that the nervus glossopharyngeus exits within the recessus scalae tympani. In one of the braincases, we found a small foramen in extreme marginal position, immediately lateral to the foramen nervi vagi, which may correspond to a foramen nervi glossopharyngealis ( fig.…”

“…3A). Computed tomographic (CT) reconstruction of the endocranium of Dasornis toliapica has shown that the os frontale overlaps the os parietale caudally, and that the two bones are unfused at the caudal region of the os frontale (Milner and Walsh, 2009). In the light of these new data, the groove in the caudal part of the cranial vault is interpreted as an incom- NO.…”

Inner ear anatomy is a proxy for deducing auditory capability and behaviour in reptiles and birds

“…Modern mCT imaging avoids these problems by providing reconstructions accurate to several micrometres of the internal space of the inner ear in intact specimens (e.g. Witmer et al 2003Domínguez Alonso et al 2004;Sanders & Smith 2005;Sampson & Witmer 2007;Sereno et al 2007;Witmer & Ridgley 2008;Milner & Walsh 2009), thus representing the maximal dimensions of the original soft tissue. However, the ECD encloses soft-tissue structures other than the basilar papilla (e.g.…”

“…the olfactory and optic lobes ;Gittleman 1991;Kalisinska 2005;Iwaniuk et al 2008;Steiger et al 2008), allowing some measure of sensory adaptation to be inferred in extinct taxa (e.g. Witmer et al 2003Domínguez Alonso et al 2004;Kundrát 2007;Sampson & Witmer 2007;Milner & Walsh 2009). …”