The Evolution of Avian Intelligence and Sensory Capabilities: The Fossil Evidence

Abstract

Crocodiles and birds are the only living representatives of Archosauria, a once diverse clade of vertebrates that mastered terrestrial, aerial and aquatic environments during the Mesozoic. Because the braincases of archosaurs are largely ossified, the group has particularly benefited from advances in non-destructive visualisation of endocranial structures over the past two decades. Here, we focus on the neurosensory evolution in the avian lineage of the Archosauria, a group in which the Bauplan of most representatives is optimised to accommodate the functional demands of flight. Neurosensory evolution in birds included a trend towards an enlargement of the telencephalon relative to the rest of the brain, an increased vestibular system sensitivity and probably also a widening of auditory frequency range and an increased reliance on visual stimuli. Despite a relatively smooth surface, bird endocasts provide crucial information on the evolution of a critical structure, the Wulst, which underwent significant enlargement during the Cenozoic and is found with highly variable form in all extant birds. With our increasing awareness of avian cognitive capacity and neural structure, the evolution of the brain in the sauropsid lineage represents an increasingly useful comparative tool against which the development of the synapsid lineage brain of primates can be assessed. Current refinements in quantification of brain structures in extant birds are improving the reliability of the information derived from the external surface of endocasts. This, in turn, should result in a better understanding of the palaeoneurology of extinct birds and other dinosaurs.