Evolution of somatic sensory specialization in otter brains



Expabsion of the coronal gyrus in Lutra and Pteroneura indicates a somatic sensory specialization of the head region, presumably in the form of extremely sensitive vibrissae. Enlargement of the primary somatic sensory projection area of the forelimb in Amblonyx, Aonyx, Parainyx and, in a different way, in Enhydra, correlates with anatomical and behavioral observations indicating increased tactile sensitivity of the hand of those otters. Fossil endocranial casts reveal that such specializations, at least in the Lutra and Aonyx groupe, were developed as far back as about ten million years ago. Potamotheirium, representing an independent line of aquatic mustelids, had an enlarged coronal gyrus 25 million years ago, at a time when in other respects it; brain was still quite primitive; descendants of Potamotherium survived until ten million years ago in North America.