Freshwater Fish Zoogeography 
37 
1 i | i — i — i — i — ] — i — i — i — i — | — , — , — ( — i — | — i — i — , — i — | — | — i — i — | — | — i — i — ( — , — • -200 
60 50 40 30 20 10 0 
E 
LATE 
E 
MIDDLE 
L 
E 
LATE 

EARLY 
M 
L 
T 
EL 
I 
PALEOCENE 
EOCENE 
OLIGOCENE 
MIOCENE 
13 
a. 
UJ 
mmJ 
CL. 
Fig. 5. Tertiary eustatic changes in sea level. Meters above or below sea level 
are tentative. From Vail and Hardenbol (1979). 
genus Jordanella has been considered to be most closely related to the 
Yucatan genus Garmanella, but recent unpublished studies suggest that 
this is not the case (J. M. Humphries, pers. comm.). The poeciliid genus 
Heterandria, which contains nine species, occurs disjunctly in southeast- 
ern United States (one species, H. formosa) (Martin 1980), and in both 
lowland and upland areas from southeastern Mexico south to eastern 
Nicaragua (Rosen 1979: Fig. 22). Movement of Heterandria stocks 
between Mexico and peninsular Florida could have occurred by direct 
migration through the ocean, perhaps aided by much lower sea levels 
that existed throughout parts of the Oligocene and Miocene, or by 
movement and subsequent elimination of coastal populations around 
the northern rim of the Gulf of Mexico. Of these, the latter possibility 
seems more likely, as indicated by (a) the absence of Heterandria from 
Cuba, and (b) the continuous distribution of another poeciliid, Poecilia 
latipinna (also absent from Cuba), around the northern rim of the Gulf 
of Mexico from Yucatan to Florida and beyond (Burgess 1980a). 
Based on a lower level of taxonomic differentiation (i.e., subspecific 
or racial), it appears likely that the group composed entirely of primary- 
division freshwater fishes evolved during the second (i.e., Pliocene) iso- 
lation of peninsular Florida. However, the species-level differentiation 
of those in the salt-tolerant, secondary-division freshwater families 
Cyprinodontidae and Poeciliidae could be interpreted as more likely 
indicating an evolutionary history dating back to the mid-Miocene iso- 
lation of the peninsula. If the above scenarios are correct, we may ask 
METERS 
