38 
Carter R. Gilbert 
why evolution of these primary and secondary freshwater groups was 
temporally separated? One possible explanation is that during the mid- 
Miocene permanent freshwater habitats were more limited in insular 
Florida, which could have prevented the establishment of such primary- 
division freshwater families as the Esocidae, Cyprinidae, Catostomidae, 
Ictaluridae and Centrarchidae. Circumstantial evidence suggests that the 
family Percidae may not have immigrated into North America by this 
time (Gilbert 1976). 
Isolation and subsequent differentiation of fishes in insular Florida 
was not necessarily confined to freshwater forms, although certainly the 
freshwater groups provide more numerous examples. Evolution of the 
two species of the genus Chasmodes (of the marine family Blenniidae) 
appears also to have occurred as a direct result of the insularization of 
peninsular Florida. Chasmodes saburrae, which apparently evolved in 
that area following isolation of part of the original Chasmodes stock, 
ranges from the upper two-thirds of the east Florida coast around the 
peninsula westward to just beyond Mobile Bay (Williams 1983: Fig. 5). 
It effectively bisects the range of the closely related C. bosquianus , 
which displays an allopatric distributional relationship to C. saburrae 
on the Atlantic coast, but a syntopic relationship to that species on the 
middle Gulf coast, from the area of Pensacola west to just beyond 
Mobile Bay. It is obvious that C. bosquianus once had a continuous 
distribution, but has subsequently become divided as a result of intru- 
sion of C. saburrae into the center of its range following geographic 
reamalgamation of insular and mainland Florida. Although Williams 
(1983) believed this to be a .pre-Pleistocene event, he did not indicate 
exactly how much earlier this might have taken place. Based on the 
discussion presented earlier, it seems likely that differentiation of the 
two species of Chasmodes occurred during the Pliocene, an hypothesis 
that is concordant with the essentially similar level of morphological 
differentiation seen in the primary-division freshwater fish species cited 
earlier. 
Peninsular Florida contains a number of faunal and floral elements 
of West Indian origin, with those groups displaying the highest levels of 
mobility or vagility being best represented (e.g., birds, flying insects, and 
many kinds of plants). A number of fish species whose ranges lie princi- 
pally in the West Indies and Caribbean areas enter United States fresh 
waters only in peninsular Florida. These include Rivulus marmoratus 
(family Cyprinodontidae), Gambusia rhizophorae (family Poeciliidae), 
Awaous tajasica and Gobionellus pseudofasciatus (family Gobiidae), 
and three species of the genus Centropomus (family Centropomidae) 
(Gilbert and Burgess 1980h; Getter 1980; Lindquist 1980; Hastings 1980; 
