Latvis/Simpson site update

By Matthew C. Mihlbachler

The Latvis/Simpson site (8Je1500) richly records a time that predates human occupation in Florida. It is filled with a detailed record of a biotic community that dates from well before the last glacial advance at the end of the Pleistocene epoch. Like Page/Ladson and many other locales along the Aucilla river, Latvis/Simpson is a sinkhole, once filled in by sediment that is now partially scoured out by the current river channel. A cross section of intact sediments remains on the west bank, cut by the river channel to form a sloping wall of clays and peats recording the last 32,000 years of environmental conditions in North Florida. In 1995, the ARPP dug a giant stairway down the west bank, from the youngest strata to the oldest, where we sampled sediments of various ages, filling in chronological gaps and environmental information for a much longer time period than previously known from the other, much younger Paleoindian sites we have excavated.

Our final season at the Latvis/Simpson site ended this past summer in late May 1998 after two and one half weeks of extra-hard work by the entire field crew. This time we concentrated on the bottom of the sinkhole, excavating a large deposit of once deeply buried, finely chopped plant remains lining the bottom of the sinkhole. Although protected for centuries by 10 meters of overburden, it is now exposed to the erosional forces of the Aucilla current, and is slowly being eaten away by this current. From dung samples collected in 1995, we knew that this unique plant layer consisted mostly of the dung remains of mastodons that had used the Latvis/Simpson sinkhole as a drinking hole and wallow 32,000 years ago. At that time, water levels were much lower, and the sinkhole was probably an isolated pool of water. The main objective of our excavations was to collect a series of mastodon digesta samples for reconstructing the diet of these extinct megaherbivores, and to compare them to the much younger mastodon digesta samples from Page/Ladson. Our efforts were fruitful and we achieved ample samples of digesta. Bill Gifford and I are painstakingly sorting through these samples (see “Wonderful Life in a petri dish”), while Lee Newsom, a botanist and anthropologist from Southern Illinois University in Carbondale, is helping us identify the plant fragments. Our preliminary view of these samples indicates that the mainstay of the mastodon diet in this region was the twigs and leaves of cypress and buttonbush. A healthy array of other species was present in the diet as well, including plums, grapes, elderberries, creeping cucumber and gourds.

As you can imagine from the size of mastodons and the large amount of plant materials that they consumed, the rate of deposition of the dung layer was quite rapid. The dung layer turned out to be about 60 cm deep and probably accounted for just a few years of mastodon activity at this sinkhole. The rapid rate of deposition caused fish, turtles and mammals that died in the sinkhole to be buried and beautifully preserved. In most cases the bones were not even fossilized but retained their original calcium phosphate and collagen matrix. As we uncovered these plant and animal remains, we realized that this site contained a singular snapshot in time of an animal community specifically adapted to cool and damp forest conditions dominated by mastodons, ground sloths, tapirs, deer, muskrats and beavers.

Our most exciting osteological find was a partial skeleton of a young female mastodon lying in the bottom of the sinkhole, buried in the digesta. The recovered material includes a pair of tusks, a complete mandible with a complete set of dentition, a pair of scapulae, a humerus, a tibia, numerous vertebrae, foot bones and ribs. Unfortunately, most of the skeleton appears to have eroded away long ago, but enough was recovered to really understand the age and health status of this animal. Paleontologists are well aware that fossil proboscideans are “filled with biology”. The slow growth rates and long life spans of proboscideans allow the skeletal elements, especially the tusks, to accumulate a wealth of information about the lives of these animals and the environments they lived in. Various aspects of the Latvis/Simpson mastodon are under study by numerous scientists for purposes of reconstructing the lives of Florida mastodons and the environments in which they lived. As part of a larger study of Florida mastodons and mammoths, scientists from the University of California at Santa Cruz sampled the enamel of the mastodon’s molars to determine the oxygen, carbon and strontium isotope signatures. Isotopic signatures provide information about diet, migration patterns and annual temperature changes in the environments that the proboscideans occupied.

At the Florida Museum of Natural History we are in the process of interpreting and reconstructing the life of the Latvis/Simpson mastodon. The first clue about its life came when we noticed that most of the bones of this mastodon are unusually porous, and a few of the ribs have pathological growths indicating that this animal may have died from some yet unidentified disease. I looked into the life history of this mastodon by analyzing the growth rings in the tusks. Tusks of proboscideans continually grow throughout life and preserve a record of each individual’s life history and its environment. Like growth rings of a tree, annually alternating dark and light bands are visible when the tusk is sliced in cross section. These growth lines record the age of the individual, the alternation of the seasons, and the growth rate and health status of the mastodon throughout its life history. With the help of a saw from the Department of Agricultural Engineering and a couple of willing hands we bravely sectioned one of the Latvis/Simpson mastodon tusks in the hope of retrieving this information. As it turns out, I counted 12-13 alternating light and dark bands (summer and winter bands), and if we add the missing two years that this animal would have had its deciduous “baby” tusks we can calculate that our mastodon was 14 to 15 years of age when it died. Although not fully grown, this mastodon was just past the age when living elephants give birth to their first offspring. Ironically, a few small, very porous, incompletely formed bones were found associated with the mastodon material that appear to be from a late stage fetus. It is likely that our unfortunate young mastodon would have been a new mother if it had not died at such a young age.