PLIOCENE-PLEISTOCENE EVOLUTION OF MARSH RABBITS

The late Pliocene Inglis 1C fauna (Citrus County, Florida) contains thousands of fossils of the extinct rabbit, Sylvilagus webbi.  Because most specimens in this collection are from immature individuals, study of the teeth involved both the occlusal and bottom surfaces.  While the occlusal views depict patterns at various ontogenetic stages, the bottom surfaces show the pattern that would be present in adult individuals.  The study of both immature and adult specimens allowed for a depiction of the ontogenetic changes undergone in the lower third premolars of S. webbi.  Very young individuals have a complete separation of the posterior and anterior sections of the occlusal surface of the lower third premolar.  A lingual wall of enamel forms later, connecting the sections.  This connection widens and encloses dentine (as in adults) prior to the development of multiple anterior reentrants.  The last feature to appear is the crenulation within the posterior external reentrant. 

Integration of this rare and detailed ontogenetic series with modern specimens from Florida and with hundreds of fossil teeth from 19 localities in Arizona, California, Florida, and Texas, yields an evolutionary scenario for marsh rabbits.  Sylvilagus hibbardi gave rise to S. webbi, and the two taxa were contemporaries for several hundred thousand years.  Sylvilagus webbi evolved anagenetically into S. palustris, which is ancestral to S. aquaticus and S. palustrellus.