University of Florida Vertebrate Fossil Locality CI001
Inglis 1A is located about 1.5 miles (2.5 km) south of the town of Inglis, on the north bank of the Cross Florida Barge Canal west of US Highway 98, Citrus County, Florida. 29.01º N; 82.69º W.
- Early Pleistocene Epoch; latest Blancan land mammal age
- 1.9-1.6 million years ago
Basis of Age
An early Pleistocene, late Blancan age is confirmed by the presence of the sloth Megalonyx leptostomus, the hyena Chasmaporthetes ossifragus, the mustelid Trigonictis macrodon, the peccary Platygonus bicalcaratus, the pronghorn Capromeryx arizonensis, the muskrat Ondatra idahoensis, and many others. Inglis 1A falls within the latest part of the late Blancan based on the co-occurrence of Sigmodon curtisi, Peromyscus sarmocophinus, and Spilogale putorius (Hulbert, 2010). The mammalian fauna is generally regarded as a close correlate of that from Curtis Ranch in Arizona, whose age is well established by magnetostratigraphy and radioisotopic geochronology.
Inglis 1A consisted from bottom to top of a basal conglomerate unit, thin bed of clay, lower sand unit, a second thin clay bed, upper sand unit, and a cemented quartz sandstone (Klein, 1971). The entire sequence varied from 3 to 4 m thick, with the two sands comprising the majority of the deposit. The two sand units also produced the majority of the fossils. The bottom of the deposit is slight below modern sea level. As no marine species were found in the deposit (except those clearly reworked from the surrounding limestone walls of the sinkhole), deposition occurred at a time when the area was inland from the coast. As this part of Florida has been uplifted by about 80 meters in the last 1.7 million years (Adams et al., 2010), global sea level was over 80 meters (260 feet) lower than it is now when the Inglis 1A sinkhole formed, placing it within a glacial period.
The site was originally a sinkhole with an opening of about 10 × 20 m. The habitat surrounding the sinkhole at the time of deposition included longleaf pine flatwoods and pine-oak scrub based on ecological interpretation of the snakes, lizards, and birds (Meylan, 1982; Emslie, 1998). Cooler summer temperatures than today is indicated by the presence of spruce pollen in the sediments (Emslie, 1998), although abundant large tortoises and armadillos imply that winters were not significantly colder than today.
Inglis 1A was a very rich deposit, producing about 18,000 identifiable fossils representing at least 161 species. The total is the second highest for any single fossil site in the state of Florida, trailing only Leisey Shell Pit 1A. All four main terrestrial vertebrate groups, amphibians, reptiles, birds, and mammals, are abundant, and both small and large species are present. All recovered fossils were isolated finds; there were no associated or articulated skeletons. Freshwater aquatic and semiaquatic species are relatively uncommon compared to purely terrestrial species, and marine species are absent.
Figure 1. The 1974 Florida State Museum Inglis 1A excavations on the bank of the Cross Florida Barge Canal. Photo by S. D. Webb.
Excavation History and Methods
The south wall of the sediment-filled sinkhole called Inglis 1A was removed during the excavation in the mid-1960s of the western portion of the Cross Florida Barge Canal. This massive federal project was to allow commercial barge traffic between the Atlantic and Gulf coasts of Florida (Noll and Tegeder, 2009). This project was eventually stopped over environmental objections, but not before the western stretch of the canal, from Lake Rousseau to the Gulf of Mexico, was completed. Fossils were discovered eroding out the remaining sediment in the sinkhole by UF paleontology graduate students Jean Klein and Robert Martin in 1967. Sporadic, small-scale collecting by FLMNH crews occurred at the site from 1967 to 1973. A major excavation lead by museum curator David Webb began in December 1973 and lasted through March 1974, with approximately 2000 person-hours invested in the work (S. D. Webb field notebook). Approximately 300 cubic meters of the fossiliferous sand layers were excavated; most of this was screenwashed on-site while the remainder was taken to the museum on the UF campus where it could be washed through screens with smaller openings. At the end of this excavation, almost all of the fossil-bearing sediments filling the sinkhole had been removed. Over the next two decades a relatively small number of specimens were found by amateur collectors, some of which were later donated to the museum. A crew comprised of students from Western State College lead by Dr. Steven Emslie and Steve and Suzan Hutchens collected the last major accumulation of fossils from Inglis 1A in April 1996, although most of their efforts were focused on the nearby Inglis 1C locality.
Inglis 1A certainly ranks in the top 10 Florida vertebrate fossils sites as ranked by scientific significance. This is based on more than just its incredibly rich fauna and large samples of many species. Nine new species were described on the basis of specimens from Inglis 1A: the toad Bufo defensor; the snake Regina intermedia; the eagle Aquila bivia; the owl Glaucidium explorator; the rabbit Sylvilagus webbi; the pocket gopher Orthogeomys propinetis; the porcupine Erethizon kleini; the fox Urocyon citrinus; and the canid Theriodictis? floridanus. As noted in the reviews of the site’s snakes and lizards by Meylan (1982) and birds by Emslie (1998), Inglis 1A provides the oldest known records of many of today’s common native Florida animals. The large number of species that dispersed from South America found in the Inglis 1A local fauna started David Webb’s interest in the Great American Biotic Interchange, a topic upon which he wrote many significant papers during his long career (e.g., Webb, 1976; Marshall et al., 1982; Webb, 1991; Webb, 2006). Specimens from Inglis 1A formed a major component if not the primarily study material for theses and dissertations of several generations of graduate students both at the University of Florida and elsewhere. Published versions of these include Steadman (1980), Frazier (1981), Meylan (1982), Wilkins (1984), and Meachen (2005). Specimens from Inglis 1A have recently been extensively used in analyses of stable isotopes of carbon and oxygen from tooth enamel to determine ancient climates and diets (DeSantis et al., 2009; Yann et al., 2013; Yann and DeSantis, 2014; Feranec and DeSantis, 2014).
It is worth noting most references written before 2005 (and a few afterwards) gave the age of Inglis 1A as early Irvingtonian and not latest Blancan as stated above. This does not mean that the relative age of the site has changed. Instead, in 2005, Bell et al. revised the boundary between the Blancan and Irvingtonian land mammal ages, moving it from about 2 million years ago to about 1.6 million years ago. Thus sites in that interval were transferred from the Blancan to the Irvingtonian land mammal age, although their geologic age remained the same.
- Original Author: Richard C. Hulbert Jr.
- Original Completion Date: April 3, 2015
- Editor(s) Name(s): Natali Valdes
- Last Updated: June 16, 2015
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.