Comparative Topics in Vertebrate Mechanoreception with a Special Focus on the Crocodilians

Abstract

Insights into the organization of vertebrate nervous systems have often arisen through systematic examinations of specific behaviors and their possible neural substrates. This approach is even more effective when diverse groups can be assessed in order to identify commonalities in innervation, anatomy, or nervous system representation. Throughout this collection of investigations, we have examined a wide-ranging group of semi-aquatic vertebrates possessing peripheral nervous system specializations related to mechanotransduction. These included a range of insectivores such the American water shrew (Sorex palustris), the smallest homeothermic diver with an elaborate array of whiskers. We also analyzed the behavior and central nervous system representations of the tentacled snake (Erpeton tentaculatus) in the process of identifying the sensory function of the unique paired facial appendage. More extensive observations were collected from two members of the order Crocodylia – the Nile crocodile (Crocodilus niloticus) and the American alligator (Alligator mississippiensis) – with particular attention devoted to their integumentary sensory organs (ISOs). These ubiquitous dome-shaped protuberances speckle the jaws of all crocodilians and are also found on the bodies scalation of members of the families Crocodilidae and Gavialidae, yet their precise function and the behaviors they mediate have remained ambiguous. We suggest that the ISOs impart an exquisite level of tactile sensitivity, even exceeding that of the primate fingertip, thereby providing a sophisticated sense of touch to an otherwise armored body surface and draw comparisons between the sensory system organization of mammalian and reptilian taxa.