Miocene Vertebrate Fossils
IntroductionUntil recently, vertebrate fossils of Miocene age (23.7 to 5.3 million years ago) have been unreported from Louisiana. The lack of such fossils had been puzzling given the broad outcrop of nonmarine strata that crosses Louisiana and the numerous vertebrate fossil sites that have been found in nonmarine strata within adjacent parts of Texas. As of early 1993, the only documented Miocene vertebrate fossil known from Louisiana was a proboscidean (ancestral elephant) fossil from Vernon Parish. A couple of fossil bird tracks from Grant Parish, once considered to be of Miocene age, have turned out to have come from older, Oligocene strata.
Proboscidean Fossil, Vernon ParishIn 1941, the first Miocene vertebrate fossil found in Louisiana consisted of the anterior end of two lower tusks (articulated mandibular) found 4.5 miles (7.2) kilometers) southeast of Leesville, Vernon Parish, Louisiana. It was found by Mr. Carl L. Hilderbrand about 21 feet, 9 inches (6.63 meters) below the surface of the ground in embedded in light-colored, sticky clay where it had been exposed and shattered by a scraper. It apparently had come to light as the result of excavations associated with the construction of U.S. Army facilities at Fort Polk. Fortunately, it had been collected by Mr. Hilderbrand and given to the U.S. National Museum (Arata 1976).
Later, Madden (1986) was able to examined this fossil, now known as USNM 16644, because it had been donated to the museum. He determined this fossil, USNM 16644, to be the remains of a gomphothere, an early ancestor of the elephant, named Gompotherium obscurum. Judging form the age of strata in which it has been found elsewhere, this gomphotherelived sometime between 15 to 5.2 million years ago.
Fort Polk Fossil VertebratesDuring Mid-1993, U.S. Army personnel at the Main Post of Fort Polk found the first large concentration of Miocene vertebrate fossils within Louisiana. In an excavation, their first find was the jaw of a small, primitive Miocene horse that was encrusted by calcium carbonate. Later examination of the site by Louisiana State University (LSU) paleontologists and them, found several other large vertebrate fossils at that site. Also, the LSU paleontologists discovered thin limestone beds that contained numerous vertebrate teeth (Schiebout 1994).
The remains of eight orders of mammals, as well as crocodile and fish remains were recovered from three sites in Fort Polk. The fossils recovered from rained-washed exposures of clay include a horse jaw, three horse teeth, a camel jaw, a fragments of a gomphothere tooth and skull, and fragments of a jaw from a deer-size artiodactyl called _Prosynthetoceras francisi_. The thin limestone beds yielded about 200 small teeth per ton of material processed for fossils. These fossils consisted of mostly teeth and other small bones of small mammals from Rodentia, Insectovora, Chiroptera, Lagomorpha, and Carnivora. In addition to these fossils, crocodile teeth and fish teeth and vertebrate have been recovered from the thin limestone beds (Schiebout 1994).
Few other types of fossils have been found in association with the Miocene vertebrate fossils at Fort Polk. The only known invertebrate fossils so far found are small, high-spired snails that are vaguely turritellid. Unfortunately, these snails are so poorly preserved that they cannot be identified. In addition to these snails, the thin limestone beds contain numerous charophytes. Charophytes are ovoid microscopic grains with spiral grooves and composed of calcium carbonate. They are the fruiting bodies of algae.
Future DiscoveriesThe above fossil discoveries clearly show that the Miocene strata of Louisiana definitely contain numerous vertebrate fossils. When people have taken the time and trouble to closely examine outcrops, they have eventually found vertebrate fossils. As indicated by other sites within adjacent parts of Texas, the rare typically, black-stained, chert gravels within the Miocene strata should be especially examined for vertebrate fossils.
The vertebrate fossils found should be mentioned to interested scientists. Furthermore, any limestone beds composed of caliche or any other carbonate concretions that lie within these Miocene strata should be reported regardless of whether they contain fossils or not. As shown above, these beds often contain numerous microscopic vertebrate fossils. Contact addresses are given below.
Dr. Judith Schiebout
Dept. of Geology and Geophysics
Louisiana State University
Baton Rouge, LA 70803
504-388-3353 - workdays
Paul V. Heinrich,
Louisiana Geological Survey
Energy, Coast, and Environment
Building, Room 3079
Louisiana State University
Baton Rouge, LA 70803
225-578-4398 - workdays
Reference CitedArata, A. A., 1966, A Tertiary probosidian from Louisiana. Tulane Studies in Geology, vol. 4, no. 4, pp. 73-74.
Jones, M. H., Schiebout, Judith A., and Kirkova, T. J., 1995, Cores from the Miocene Castor Creek Member of the Fleming Formation, Fort Polk, Louisiana: relationship to the outcropping Miocene terrestrial vertebrate fossil bearing beds (CORE). Transactions of the Gulf Coast Association of Geological Societies. vol. 45, pp. 293-202.
Madden, C. T., 1986, Gomphothere proboscidean Gomphotherium from Miocene of Louisiana. Abstracts with Programs Geological Society of America. vol. 18, no. 3, p. 252-253.
Schiebout, Judith A., 1994, Fossil vertebrates from the Castor Creek Member, Fleming Formation, western Louisiana. Transactions of the Gulf Coast Association of Geological Societies. vol. 44, pp. 675-680.
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Dec 18, 2001Copyright ｩ 1996-2002 Paul V. Heinrich All rights reserved.