50 Timothy S. Young and Joshua Laerm 



fauna is clearly mixed and reflects heterochronous deposition over 

 time beginning no later than the late Pleistocene (Wisconsinan) and 

 extending through the Recent. 



We compared the St. Marks River faunal list and a modern 

 regional faunal list of the Apalachicola River system (Means 1976). 

 Of the 344 species listed by Means, 29% of the mammals, 10% of 

 the birds, 19% of the reptiles, 5% of the amphibians, and 2% of 

 the fish are represented in the St. Marks River fauna. This bias 

 toward mammals probably reflects taphonomic factors associated with 

 the larger size of mammalian elements in a fluvial environment. Small, 

 more fragile vertebrates (birds, reptiles, amphibians, and fish) are clearly 

 under-represented in the St. Marks River fauna. This bias is reflected 

 also in the mammalian fauna where chiropteran, insectivoran, and small 

 rodent remains are conspicuously absent. 



While many of the species recovered from the St. Marks River 

 are eurytopic and provide only limited information regarding the 

 environment of deposition, a number are stenotopic and are considered 

 good environmental indicators. 



Mammals — The mammalian fauna, in particular, is very useful 

 in assessing the chronology and paleoenvironment of the St. Marks 

 River. The reason for this is two-fold. First, mammals are the most 

 numerous and have the largest component of extinct forms. Second, 

 Florida has an extremely rich and well-documented late Pleistocene 

 as well as modern mammalian fauna upon which comparisons to the 

 St. Marks River fauna can be made. 



Thirteen (35%) of the mammalian fauna of the St. Marks River 

 is represented by extinct forms. These include Holmsina septentrionalis, 

 Megalonyx jeffersonii, Glossotherium harlani, Canis dims, Smilodon 

 sp., Synaptomys australis, Tapirus, sp., Equus sp., Platygonus 

 compressus, Hemiauchenia macrocephala, Paleolama mirifica, 

 Mammut americanum, and Mammuthus jeffersonii. This closely 

 approximates the relative percentage of extinct mammals from a 

 number of Rancholabrean faunas from elsewhere in Florida (Martin 

 and Webb 1974). The temporal span of the extinct forms ranges 

 from Blancan through Recent. However, they all share a late 

 Wisconsinan chronology. Those species representing extant forms, 

 although individually some exhibit a longer stratigraphic history, also 

 share a late Wisconsinan chronology. With few exceptions, all the 

 extant species are represented in the local fauna today. 



Comparison of the known and inferred habitat preferences or 

 requirements of the extant and extinct mammalian species suggests 

 the depositional environment was heterogeneous. On one hand there 

 are a number of essentially woodland species: Didelphis, Holmsina, 



