Withlacoochee River 1A

University of Florida Vertebrate Fossil Locality MR060

Location

In channel of Withlacoochee River about 10 miles southeast of Dunnellon, Marion County, Florida; 29.0° N, 82.3° W.

Age

Early Pleistocene Epoch; later half of Blancan land mammal age
About 1.9 to 2.2 million years old

Basis of Age

Vertebrate biochronology (presence of Megalonyx leptostomus, Sigmodon medius, Nannippus peninsulatus, and Hemiachenia gracilis, species only known from late Blancan localities in Florida).

Geology

Fossils derive from a sandy gray clay filling shallow depressions and crevices in an irregular limestone surface.

Depositional Environment

Clay probably represents the remnants of material filling an ancient sinkhole.

Fossils

Excavation History and Methods

Discovered by Aaron Gipson in 1995. Collected by A. Gipson, Dawn Gibson, and friends and relatives between 1995 and 2014 (collecting still on-going as water conditions permit). Specimens donated to the Florida Museum of Natural History. Additional collecting by A. Gipson, D. Gibson, and Florida Museum of Natural History field crews in the spring of 2009 and 2011, including large samples of matrix for screenwashing (diver in Figure 1 is collecting in situ clay from a limestone depression). About 2,100 cataloged specimens in the Florida Museum of Natural History collection, along with a backlog of about 1000 unidentified specimens.

Figure 1. Former UF grad student Alex Hastings collecting in situ fossiliferous sediment at the Withlacoochee River 1A site in 2009.

Discussion

The only known Florida locality with both Paramylodon harlani and Nannippus peninsulatus. Therefore, one of the youngest, if not the youngest, record of three-toed horses in North America. The fossils are found along about a 30-yard-long stretch of the river at a depth of two to six feet (1-2 meters). Freshwater species are relatively rare; small tortoise shell elements and armadillo osteoderms both very common. Although primarily represented by postcranial skeletal elements, mammalian carnivores are remarkably diverse at Withlacoochhee River 1A (nine species, see faunal list). Most of this important fauna has not yet been studied.

Original Author(s): Richard C. Hulbert Jr.
Original Completion Date: January 30, 2009
Editor(s) Name(s): Richard C. Hulbert Jr., Natali Valdes
Last Updated On: July 20, 2020

This material is based upon work supported by the National Science Foundation under Grant Number CSBR 1203222, Jonathan Bloch, Principal Investigator. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Withlacoochee River 1A