ENDOCRANIAL ANATOMY OF A PALEOCENE STEM WATERFOWL (AVES, ANSERIFORMES)

TAMBUSSI, C.P.; SANTILLANA, S.N.; WITMER, L.; DEGRANGE, F.J.; DEMMEL FERREIRA, M.M.

Puerto Madryn

Congreso; Reunión de Comunicaciones de la Asociación Paleontológica Argentina 2018; 2018

Morphology of the avian brain is of criticalimportance for studies on the evolution of modern birds, and especiallyimportant is the information provided by stem avian fossils. Here we present areconstruction of the endocranial morphology based on computed tomography of astem representative of Anseriformes of early Paleocene age (Danian). The fossil(MLP 07-III-1-1) comes from the López de Bertodano Formation(Maastrichtian-Danian) of Seymour Island, West Antarctica. The brain cast showsa wide telencephalon, small optic lobes, large olfactory bulbs, a short andwide cerebellum, and a wide medulla oblongata. Viewed laterally, it displays aslight flexure of the main brain axis, and the telencephalon completely covers themesencephalon in dorsal view. No telencephalic Wulst is present, suggestingthat this innovative avian neurological peculiarity was not recognizablydeveloped 65.5 Myr ago. Morphology was closer to that of the Eocene anseriform Presbyornis due to the presence of largeolfactory bulbs, stout flocculi that are caudolaterally directed, and also theabsence of the Wulst. Absence of the Wulst and small optic lobes seems toindicate that stem Anseriformes were not strongly visually oriented birds whereasits large olfactory bulbs would denote significant olfactory capabilities. Incrown Anseriformes (as in most modern birds), the condition is the opposite. Consequently,the brain morphology of the new Antarctic fossil is consistent withmorphological trends seen in living birds: replacement of olfactory sensory inputby enhanced vision.