Guiana dolphins (Sotalia guianensis), which inhabit the Caribbean and waters along Atlantic coasts of Central and South America, can sense electrical activity in the water using hairless follicles on their rostrums, where a land mammal’s whiskers would be. Once thought to be nonfunctional remnants of their land-dwelling ancestors, these so-called vibrissal crypts contain dense populations of nerves (about 300 axons per crypt), as well as intraepithelial nerve fibers, suggesting the structures may serve a sensory purpose, according to a paper published yesterday (July 26) in Proceedings of the Royal Society B. The study's authors confirmed this hypothesis by exposing a captive Guiana dolphin to electrical fields of various strengths. The animal could sense and respond to low electrical signals, but did not react to even high-intensity electric fields when its crypts were covered with a plastic shell.
Such passive electroreception has been widely documented in fish and amphibians, and has even been studied in egg-laying mammals, such as the platypus. But this is the first evidence that some true mammals also have this sensory capability, suggesting electroreception may be more widespread than previously believed, and can evolve from a mechanosensory organ possessed by nearly all mammals.