The brain of Leptictis dakotensis, an Oligocene leptictid (Eutheria; Mammalia) from North America

Observations of previously undescribed endocasts referable to the Oligocene leptictid Leptictis dakotensis yield new and revised information on the brain features of this species. The neocortex is larger relative to other regions of the brain than in several Recent lipotyphlous insectivores. There is also evidence for two small neocortical sulci in Leptictis. The estimated range of encephalization quotients (EQ's) for this species, assuming a wide range of body weights, is 0.450.70. Relative brain size in this animal is therefore possibly greater than in most Recent insectivores for which data are available. Only elephant shrews (macroscelidids) and a few specialized lipotyphlous insectivores show a significantly greater degree of encephalization. The Leptictis EQ estimates are also comparable to those in some early prosimians but are notably lower than such estimates for later Tertiary and Recent primates. Leptictis is a relatively derived leptictid, and the only member of the family represented by well-preserved endocranial features. The genus does not represent an appropriate model for the primitive brain condition in primates and insectivores.