The functional anatomy of elephant trunk whiskers.

Behavior and innervation suggest a high tactile sensitivity of elephant trunks. To clarify the tactile trunk periphery we studied whiskers with the following findings. Whisker density is high at the trunk tip and African savanna elephants have more trunk tip whiskers than Asian elephants. Adult elephants show striking lateralized whisker abrasion caused by lateralized trunk behavior. Elephant whiskers are thick and show little tapering. Whisker follicles are large, lack a ring sinus and their organization varies across the trunk. Follicles are innervated by ~90 axons from multiple nerves. Because elephants don't whisk, trunk movements determine whisker contacts. Whisker-arrays on the ventral trunk-ridge contact objects balanced on the ventral trunk. Trunk whiskers differ from the mobile, thin and tapered facial whiskers that sample peri-rostrum space symmetrically in many mammals. We suggest their distinctive features-being thick, non-tapered, lateralized and arranged in specific high-density arrays-evolved along with the manipulative capacities of the trunk.

Coevolution of rostrum and brain in pig species.

Domestic pigs have a prominent cortical gyrus (the rostrum gyrus) isomorphic to the contralateral hemirostrum. It is unclear, however, if the size and shape of the rostrum gyrus are of evolutionary/functional relevance. Here, we address this question by assessing the relationship of rostrum and rostrum gyrus across eight pig species. To this end, we quantified rostrum morphology in fresh and alcohol-preserved pig specimens by surface scans, microfocus computed tomography scans, and photography. We establish that the size and shape of the rostrum gyrus can be precisely inferred from endocasts. We then took advantage of the accessibility of pig skulls and endocasts to assess features of the rostrum gyrus across species. Our investigation led to the following results: (i) The rostra of pig species show basic similarities. (ii) A cortical rostrum gyrus is apparent in all pigs. (iii) The size of the rostrum gyrus differs across species and outgroups of the evolutionary dominant suinae (i.e., peccaries and the babirusa) have a noticeably smaller rostrum gyrus. (iv) Warthogs have a derived rostrum morphology with an extra fold and a very wide rostrum; the warthog rostrum gyrus recapitulates these rostrum features. (v) Domestic pigs have relatively smaller rostrum gyrus than wild boars. We also provide indications for a conserved cytoarchitectonic patterning of the rostrum gyrus. We conclude that the rostrum gyrus is a neural module that was putatively present in the common ancestor of pigs and that this neural module is conserved across pig species. Natural selection maintains the rostrum gyrus' size and its exact isomorphism to the rostrum.