Pleistocene Mammals Central Florida 79 



is Recent or even unfossilized (e.g., some of the Equus and Odocoileus). 

 In addition, some Miocene fossils of marine invertebrates and sharks 

 have eroded from the limestone bedrock through which the stream 

 flows. The late Pleistocene fossilized materials represent accumulation 

 in two types of situations: one of higher sealevels and another of much 

 lower sealevels. The cetacean vertebra, the barnacle-covered Mylohyus 

 dentary, and the Trichechus material comprise evidence of marine intru- 

 sion. The last time seas could have covered the Rock Springs locale 

 (elevation 7 m above present sealevel) was some 125,000 years before 

 present (ybp). According to eustatic studies, 125,000 ybp was the most 

 recent occasion that seas have been higher than at present (Shackleton 

 and Opdyke 1973; Bloom et al. 1974; Chappell 1974). In Florida, this 

 late Sangamonian interglacial transgression corresponds to the Pamlico 

 shoreline at about 9 m (Healy 1975). It is possible, yet unHkely, that 

 some earlier transgressions of similar or greater extent introduced the 

 marine influence. Thus, the cetacean, the barnacles encrusting the 

 previously-deposited peccary jaw, and at least some of the sirenian 

 material are probably of Sangamonian age. 



Most of the terrestrial vertebrates presumably were deposited dur- 

 ing one or more phases of reduced sealevel. During at least one such 

 interval, sealevel and the piezometric surface dropped sufficiently to 

 produce habitats suitable to vertebrates that do not now occur in east- 

 ern North America. Woolfenden (1959) noted a western contingent in 

 the Rock Springs avifauna. A portion of the Rock Springs mammal 

 fauna also exhibits noneastern United States affinities. Smooth-toothed 

 pocket gophers (genus Thomomys) are known from the Rock Springs 

 deposit, but the genus now occurs only in Mexico and western North 

 America (Hall 1981). The range of Mormoops megalophylla is now res- 

 tricted to the southwestern United States, southward through much of 

 Central America and into northern South America (Smith 1972). Mor- 

 moops blainvilli, the only other extant species of the genus, occurs in 

 the West Indies (Hall 1981). 



Paleoenvironmental Interpretations 



The genus Mormoops (as well as the species M. megalophylla 

 itself) is neotropical and temperate in distribution and occupies humid 

 to semiarid to arid situations at elevations generally less than 3000 m 

 (Smith 1972). Similarly, Thomomys pocket gophers occupy habitats 

 including deserts, prairies, montane meadows and forests ranging over 

 some 35 degrees of latitude and 3000 m of elevation. It is apparent that 

 no single temperature or rainfall regime characterizes the entire range of 

 either genus. Therefore, because of their broad habitat and environmen- 

 tal tolerances, the presence of M. megalophylla or Thomomys at Rock 

 Springs need not be directly indicative of any particular habitat types. 



