34 
Carter R. Gilbert 
Recent papers by Vail et al. (1977) and Vail and Hardenbol (1979), 
which discuss sea-level changes during the Cenozoic, have done much to 
clarify this situation. However, this picture has subsequently been modi- 
fied somewhat by the findings of Opdyke et al. (1984), who presented 
evidence to show that peninsular Florida and closely adjacent areas 
have undergone epeirogenic uplift during the late Cenozoic. One impor- 
tant consequence of this is that present elevations of the various marine 
terraces may be exaggerated in terms of reflecting changes in sea level. 
For example, the Cody Scarp (or Wicomico Shoreline) is at an eleva- 
tion approximately 30 m above present mean sea level; however, the 
actual drop in sea level may have been somewhat less than 30 m, with 
the difference being accounted for by epeirogenic uplift. Unfortunately, 
the exact relative contributions of the two events cannot be determined 
with certainty. Despite this new complication, the picture presented 
below regarding isolation and evolution of faunal elements in peninsular 
Florida correlates well with the sequences of rise and fall in sea level 
presented by Vail et al. (1977) and Vail and Hardenbol (1979). It corre- 
lates so well, in fact, that I must conclude that epeirogenic uplift, 
although an important consideration, does not significantly change the 
basic scenario. 
Cooke (1945) presented the first thorough summary of Florida sea- 
level stands. He envisioned the periodic separation and rejoining of 
peninsular Florida and the mainland to be essentially a Pleistocene 
event. Alt and Brooks (1965) and Alt (1968) regarded the isolation of 
these peninsular islands as having occurred earlier, with the last com- 
plete separation being no later than the first (Aftonian) interglacial, if 
then. They pointed out that pre-Pleistocene sea levels were higher than 
subsequently, this presumably related to the fact that large amounts of 
sea water were not then tied up in glacial ice. If so, this would suggest a 
continuous pre-Pleistocene isolation of the peninsular islands from the 
mainland. This assumption, however, is at odds with the fact that var- 
ious freshwater fishes that are intolerant of sea water (Myers’ [1938] 
primary-division groups) almost certainly had reached peninsular Flor- 
ida earlier, where they remained isolated sufficiently long to permit well- 
defined racial or subspecific differentiation to occur. 
Peninsular Florida is thought to have had its origin during the 
middle Oligocene epoch, probably around 30 million years before pres- 
ent (B.P.). This event is correlated with an unusually severe drop in sea 
level, perhaps as much as 250 m (Vail et al. 1977, Vail and Hardenbol 
1979), which in turn appears to be correlated with formation of the 
Antarctic ice cap (Miller et al. 1985, Prothero 1985, Savin and Douglas 
1985). Major mid-Oligocene cooling and circulation events are sug- 
gested by the benthic foraminiferal <5 l8 0and planktonic foraminiferal 
