Ichetucknee River

University of Florida Vertebrate Fossil Localities CO001, CO028, CO031, CO042, CO043, CO044, CO045, CO046, CO053, CO063, CO064, CO065, CO066, CO067, CO068, CO069, CO081, CO086, and CO087

Location

The river is about 4.1 miles (6.7 km) northwest of Fort White, Columbia-Suwannee county line, Florida. 29.96º N; 82.78º W (For most of its length, the river forms the boundary between Columbia and Suwannee counties; however, the Ichetucknee Head Spring and the initial part of the river actually lie within Suwannee County. For the sake of convenience and uniformity, in the UF database and collection, all Ichetucknee River fossils are regarding as coming from Columbia County).

Age

• Late Pleistocene Epoch; late Rancholabrean land mammal age
• 50,000-11,000 years ago

Basis of Age

Biochronology (co-occurrence of Sigmodon hispidus, Microtus pinetorum, Puma concolor, Panthera atrox, and Bison antiquus) indicates a late Rancholabrean age (Webb, 1974). Presence of Eremotherium laurillardi suggests that at least some of the fossils are in the range of 25 to 50 thousand years ago (Thulman and Webb, 2001; Fields et al., 2012).

Geology

The Ichetucknee River flows for about 5.5 miles (8.8 km) in a generally southerly direction. It originates from many springs, several of which are of first or second magnitude, and ends at the Santa Fe River (Scott et al., 2004). Vertebrate fossils have been found in the bed of the river, along its entire length, as well as in some of the individual springs and the channels connecting them to the river. The following is mostly taken from Auffenberg (1957, 1963), who provided the most detailed descriptions of the geology of the region.

The primary, undisturbed, fossil-bearing unit found along the banks of the river is a gray to white sandy clay that grades to pure sand. This unit is about 3 feet (1 m) thick. Above this is a bed of loose to moderately compact, gray clay that is 7-10 feet (2-3 m) thick. This unit contains bones of varying degrees of mineralization. Both of these beds are below the water level during intervals of normal flow. At the top of the sequence, rising above the water level, is a layer of brown silt and clay that also contains bones that vary in their degree of mineralization. According to Auffenberg (1963), the lowest unit is late Pleistocene in age, while the highest is essentially modern. He does not give an age for the middle unit, but does note that it has a much greater number of deer bones than does the lowest unit. This suggests its age is early or middle Holocene. The upper two beds do contain some Pleistocene fossils, but Auffenberg (1963) regards them as being reworked out of the lowest level. Others working with fossils from the Ichetucknee River have also emphasized that they are of mixed age (e.g., McCoy, 1963; Kurtén, 1965)

Auffenberg (1957) describes a somewhat similar sequence within Blue Spring. At the base of the sequence is a soft, reddish orange clay that contains late Pleistocene fossils without any modern contamination. Above this is a freshwater marl primarily consisting of cemented shells of the snail Pleurocera. The marl contains abundant, relatively complete specimens of emydid and chelydrid turtles and alligators, along with more isolated specimens of terrestrial mammals. Fossil bones from these two layers are much lighter in color than those typically found in the Ichetucknee River. Overlying the marl is a modern deposit rich in loose snail shells and unconsolidated sediment that contain a chronologically mixed assemblage of Pleistocene fossils, prehistoric artifacts, and modern debris such as lead fishing sinkers.

Depositional Environment

A mixture of stream, pond, and marsh deposits (Auffenberg, 1963).

Fossils

The combined number of vertebrate fossils from the Ichetucknee River in the Florida Museum of Natural History collection is over 11,000. Smaller collections are in the Museum of Comparative Zoology at Harvard University, the American Museum of Natural History, and probably others. The springs and river were a popular recreational destination for many decades prior to it becoming a state park in the 1970s, and so it must be assumed that numerous specimens ended up in private collections. A large percentage, perhaps as much as half, of the specimens in the UF collections appear to be of Holocene age. Most specimens lack precise collecting data, and were evidently not collected from in situ Pleistocene deposits. Those specimens lacking provenience from taxa that became extinct at the end of the Pleistocene can be assumed to be late Pleistocene, although they may not all be contemporaneous. Those from taxa that persisted into the Holocene are of suspect age and their preservation must be examined individually on a case by case basis. Some associated skeletons and complete skulls are known, but most specimens consist of partial jaws and isolated teeth and postcranial bones. Preservation varies widely from excellent to poor.

The following list of species consists of all vertebrate species whose bones were found in the Ichetucknee River, excluding only those of domesticated animals introduced by European settlers (pigs, cattle, etc.). As discussed above, species which are still living or who historically lived in the region, may in fact not be represented by any late Pleistocene specimens, only those of Holocene age. No one has as yet thoroughly and methodically analyzed the entire collection to make such a determination.

Excavation History and Methods

The oldest collected specimens in the UF collections date to the mid-1920s. The majority of the specimens were found in the 1950s and 1960s. There are no records of major, extensive excavations by museum crews of submerged in situ deposits such as occurred in the Santa Fe and Withlacoochee Rivers in the 1960s and the Aucilla River in the 1980s and 1990s. Collecting in the Ichetucknee appears to have been a more haphazard affair, although certainly dive crews from the museum worked it many times in the 1960s, but primarily collecting specimens from or near the surface of the river bed. Small vertebrate fossils are relatively rare, suggesting limited collection of sediment for screenwashing (a difficult but not impossible task in submerged deposits).

As in all Florida state parks, absolutely no fossil or artifact collecting is allowed in the Ichetucknee River or any of its source springs within the boundaries of the Ichetucknee Springs State Park. Effectively, this means the portion of the river north of the US Highway 27 bridge. Fossil collecting is allowed with a valid permit on the lower portion of the river, from the US 27 bridge to its confluence with the Santa Fe River.

Discussion

The issues of mixed chronology and lack of precise collecting data have limited the overall scientific significance of the rich sample of fossils from the Ichetucknee River. For example, Ruez (2011) studied what he termed the largest known Pleistocene assemblage of the marsh rabbit in Florida. But it is possible, even likely, that some of the specimens are actually early Holocene, or even late Holocene. In the study of the birds by McCoy (1963), the author stated that he only included well mineralized specimens. But Neil (1957) discussed this issue and noted that not even the degree of mineralization could reliably distinguish between Pleistocene and Holocene bones from Florida springs and rivers. The Ichetucknee River sample of beaver (Castor canadensis) was specifically discussed by Neil as one whose age was questionable.

Certainly there are individual specimens from the Ichetucknee River that are by themselves highly significant. Foremost among them is the nearly complete skull and lower jaws of the American lion (Panthera atrox) shown in Figure 1. This is the most complete specimen of the species found in the eastern United States. It was extensively studied by Kurtén (1965). The Ichetucknee River has also produced one of the largest samples of the sabertoothed cat Smilodon fatalis in Florida (also studied by Kurtén, 1965), as well as a relatively large sample of the giant capybara Neochoerus pinckneyi. There are also partial skeletons of both a tapir and a bison.

Sources

• Original Author: Richard C. Hulbert Jr.
• Original Completion Date: May 4, 2015
• Editor(s) Name(s): Richard C. Hulbert Jr., Natali Valdes
• Last Updated On: June 10, 2015

Copyright © Florida Museum of Natural History, University of Florida