P1.105 Wednesday, Jan. 4 Gross Anatomical Brain Region Approximation (GABRA): a new technique for assessing brain size and structure in extinct archosaurs MORHARDT, A.*; RIDGELY, R.; WITMER, L.; Ohio University; Ohio University; Ohio University email@example.com
Studying brain evolution in extinct taxa is difficult due to the potential lack of close correspondence between the brain and its bony braincase. Cranial endocasts may be good proxies in certain groups (mammals, birds), but the brain does not fill the endocranial cavity in many reptiles, making their endocasts less reliable indicators of brain size and morphology. Thus, assessments of relative brain size and brain-region evolution often require untested assumptions. We propose the use of a new technique known as Gross Anatomical Brain Region Approximation (GABRA), which involves importing a digital endocast derived from CT scanning and 3D visualization software into modeling software (Maya). Brain regions underlying the digital endocast are modeled as ellipsoids, the limits of which are based on the osteological correlates of soft-tissue structures visible on endocasts, as identified by comparison with extant taxa. These discernable structures (neurovascular canals, dural sinuses, fossae produced by the brain itself, etc.) provide limits on the location and size of major brain regions (e.g., cerebral hemispheres, cerebellum, optic lobes, olfactory bulbs). GABRA criteria were validated in extant archosaurs (birds, alligators) with gross dissection, CT scanning of Lugol’s-iodine-soaked specimens, and MRI data. Preliminary GABRA brain results of dinosaur taxa are credible. Ultimately, GABRA allows moving beyond studying the cranial endocast as a singular entity to studying the evolution of the brain and its different parts, allowing hypotheses of neurological mosaic evolution to be better tested. Moreover, revised estimates of brain and brain-region dimensions will provide a better basis for quantitative analyses of relative brain size.