USING MODERN LLAMA BRAINS AND CRANIAL ENDOCASTS TO STUDY BRAIN EVOLUTION IN FOSSIL CAMELS

Fossil cranial endocasts – natural casts of the inside of the cranium -- are sometimes very detailed, and are therefore potentially useful for the study of brain evolution. An important preliminary for such study, however, is knowledge of what parts of the brain can be expected to be well enough preserved to be adequately characterized. As part of a study of endocasts of the Oligocene American camelid Poebrotherium, we compared the brain of a close living relative, Lama pacos (llama), to a silicone cast of the llama’s cranial cavity. Thirteen features of the brain were chosen for examination based on their relative functional importance and overall visibility and ease of detection. These included the longitudinal fissure, sulci, gyri, size and overall preservation of the neocortex, the mastoid fossa, the rhinal fissure, olfactory bulbs, cerebellum, hypophysis, vermis, cranial nerves, the pons, and the fissure lateralis cerebri. Of these 13 features, only 8 could be examined in sufficient detail in the silicone endocast, and therefore could be expected to be preserved in fossil endocasts. The 5 features that are not expected to be preserved include the rhinal fissure, olfactory bulbs, cranial nerves, pons, and the fissure lateralis cerebri. Examination of 3 fossil Poebrotherium endocasts in museum collections confirms that these features are not preserved well enough to be characterized. Future studies of camelid brain evolution should therefore focus on the 8 preservable features: the longitudinal fissure, sulci, gyri, size and overall preservation of the neocortex, the mastoid fossa, cerebellum, hypophysis, and the vermis.