Meeting Abstract
Avian brain endocasts are relatively faithful representations of the external morphology of the brain, and in extinct birds, they are the only source of information on brain anatomy. The volumes of some brain structures in extant birds have been correlated with the complexity of the behaviors that they mediate. Often, these correlations are used to make inferences about behavior in extinct birds, but these inferences are based on endocast structures and rely on the assumption that the surface area of an endocast structure is a fair proxy for the volume of the underlying brain structure. However, this assumption has not been tested and may be problematic because the endocast only allows measurement of the surface area of externally-visible portions of brain structures. The optic lobe, which overlies the optic tectum, and the Wulst, which overlies the hyperpallium, are two endocast structures which are consistently expressed in birds and whose associated brain structures are involved in avian visual pathways. The relationships of these brain and endocast structures were assessed in 20 extant avian taxa. For each species, optic tectum and hyperpallium volumes, compiled from the literature, were regressed on the surface areas of the optic lobe and Wulst, measured from endocasts generated from CT scan data. These preliminary results indicate that there is a positive relationship between endocast structure surface area and brain structure volume in the studied vision-related structures, which was then used to predict the volumes of these brain structures in five extinct avian taxa (Archaeopteryx, Dinornis, Lithornis, Presbyornis, and “Buteo” grangeri). This taxonomic sample will be expanded in the future to strengthen these relationships and extend the study of brains and behavior of birds into deep time.
