Freshwater Fish Zoogeography 
39 
Burgess 1980c,d,e). Other freshwater fishes of similar origin range only 
a short distance beyond Florida. All the above species are completely 
salt tolerant, and thus are subject to continual recruitment from farther 
south. Furthermore, in none of the above cases has the Florida popula- 
tion been shown to differ taxonomically from those elsewhere. 
ORIGIN OF ST. JOHNS RIVER DRAINAGE 
Previous reference has been made to the complex origin of the St. 
Johns River drainage and to the fact that, although it falls into the 
faunal cluster with those drainages immediately to the north (Fig. 2), it 
could equally well be included with those occurring in the southern part 
of peninsular Florida. Partial evidence for this is based on the taxo- 
nomic character of Micropterus salmoides, Lepomis macrochirus , 
Lepomis marginatus, Notropis emiliae and Ictalurus natalis, each of 
which has undergone genetic differentiation in peninsular Florida, with 
the peninsular form in each case being found in the St. Johns drainage. 
The St. Johns River historically was an ocean estuary with a north- 
south orientation determined by a series of barrier islands that parallel 
the coast and separate the river from the Atlantic Ocean. These islands, 
which collectively have been termed the “Atlantic Coastal Ridge,” 
appear to have been formed during Pamlico time (Yarmouth intergla- 
cial), when sea level was about 8 to 10 m highei than at present (White 
1970: 86). Most of the drainage was inundated during the Pliocene, the 
only areas not so covered being several tributaries flowing off higher 
ridges in the Palatka area, to the west, and a relatively small section in 
the upper (i.e., southern) part of the drainage (Burgess and Franz 1978) 
(Fig. 4). The latter included part of the upper Oklawaha River system, 
as well as that area included in the present-day Ocala National Forest 
(the so-called “Ocala scrub”), which is situated between the Oklawaha 
and St. Johns rivers. During the Pleistocene interglacial periods, partial 
inundations of the peninsula occurred, with each successive inundation 
covering less of the peninsula than before (Alt and Brooks 1965). 
The only endemic fish in the St. Johns drainage is the taxonomi- 
cally weakly defined Cyprinodon variegatus hubbsi, which occupies six 
lakes in the upper Oklawaha River system (Weir, Harris, Eustis, Yale, 
Griffin and Dora) (Johnson 1974, 1980). The precursor of this form 
(presumably very similar to C. v. variegatus ) is believed to have reached 
this area during either the Pliocene or early Pleistocene, when sea levels 
were highest, and evolved to its present taxonomic level during the 
Pleistocene. Cyprinodon v. variegatus , although tolerant of fresh water, 
is basically an inhabitant of brackish water, and the progressively lower 
sea stands during successive Pleistocene interglacial periods would have 
