Abstract
Teratornithidae is an extinct bird family, likely related to Cathartidae, known exclusively from the Americas. They were once thought to be scavengers, but recent theories suggest they were opportunistic or piscivorous birds capable of swallowing prey whole. The most notable species, Argentavis magnificens, had a wingspan of 6 to 8 m and weighed 70 to 80 kg. In order to infer paleobiological aspects of this bird, its endocast (as a proxy for brain morphology), reconstructed from computed tomography scans of the holotype skull, is here described and compared to that of other bird species of zoophagous feeding habits with different flight styles. The brain of Argentavis presents a general appearance similar to that of Cathartidae, being dorsoventrally flattened and anteroposteriorly elongated, with small optic lobes in relation to the total encephalic surface. The estimated volume of the bulbi olfactorii is very similar to that of the Andean Condor Vultur gryphus. The main difference observed with Cathartidae is the marked development of the eminentiae sagittales present in Argentavis (structures closely related to the perception of visual information), which are more similar to those of the Accipitriformes and Falconiformes analyzed. The results obtained here suggest that Argentavis was a scavenger or even maybe a kleptoparasitic bird, relying more on vision than on smell (similar to that observed in the Andean Condor). Furthermore, the inner ear and flocculi exhibit characteristics similar to birds without acrobatic flight, indicating that Argentavis had a soaring flight and inhabited open areas without much vegetation.