Difference between revisions of "Mammal Fossils"
Revision as of 16:18, 24 April 2013
Paleoindians sometimes hunted mastodons until these giant mammals died out at the end of the Ice Age.
Mammals first appeared during the Triassic Period and lived with dinosaurs during the Mesozoic Era. At the beginning of the Cenozoic Era, after extinction of the dinosaurs about 65 million years ago, mammals flourished and diversified. However, similar to the Mesozoic Era, Ohio was an upland land mass and erosion removed large quantities of rock. It is probable that mammals roamed Ohio just as had the dinosaurs but no rocks, and therefore no mammal remains from the Paleogene and Neogene Periods are preserved in the state. It was not until the Pleistocene Ice Age that remains of mammals were entombed and preserved in sediments.
Most, if not all, mammal remains from Pleistocene sediments in Ohio represent the last part of the Ice Age (Wisconsinan) and many sites yield radiocarbon dates that place them very near the end of the Ice Age (10,000 years ago) when glacial ice had been gone from the state for several thousand years. Most of the fossil-bearing deposits represent former glacial lakes and ponds that are now swampy areas. Excavation of these deposits sometimes yields large bones that are easily recognized as unusual. Isolated teeth, tusks, and bones are commonly picked up along streams and rivers in sand and gravel deposited as outwash of from melting glaciers. These specimens are commonly broken and water worn. The best specimens and the greatest faunal diversity are from deposits preserved in caves and sinkholes. Only one such deposit is known from Ohio, although they are abundant in other states with better development of caves.
It would be surprising to many people to learn that of the 40 species of mammals known from Ohio�s Pleistocene deposits, 29 species still survive in North America Of these, 21 species still live in the state. A significant extinction event at the end of the Ice Age selectively removed large mammals, collectively known as the megafauna.
Without question the most significant and well-known extinct Ice Age animal found in Ohio was the American mastodon, Mammut americanum. Although most specimens consist of isolated teeth or tusks, a number of nearly complete specimens have been found. Several are on display at museums in the state, including the famous Conway mastodon displayed at the Ohio Historical Society. Mastodons were elephant-like animals that were sturdily built browsers of open spruce forests. Adults stood about nine feet high at the shoulder and they weighed between four and five tons. Their cone-shaped teeth are distinctive. Most complete specimens have been found in the sediments of former glacial lakes where they broke through the ice in winter or became bogged down in mud. Some specimens show evidence of having been butchered by Paleoindians.
Mammoths were elephants that are related to the modern Indian elephant. They were more slimly built than mastodons and were primarily grazing animals more common to grasslands. Although mammoth remains are not uncommon in Ohio, they are decidedly less common than are the remains of mastodons. Two species of mammoth have been recognized in Ohio: Mammuthus primigenius, the northern mammoth, and Mammuthus columbi, a more southerly species. Both mastodons and mammoths became extinct about 10,000 years ago.
A large and bizarre animal that inhabited Ohio during the Pleistocene and became extinct at the end was the ground sloth. These ox-sized animals migrated northward from South America during the Ice Age and are occasionally found in bog deposits in Ohio. They had large, strong front legs with claws that were used to obtain vegetation.
Remains of horses, mostly isolated teeth and jaws, that lived in Ohio during the Pleistocene have been found occasionally. Remains of a tapir, another southern migrant, have also been found.
Bones of an extinct, pig-like peccary species, Platyogonus compressus, have been reported from several sites in Ohio, including nearly complete specimens. Excavations at Indian Trail Caverns in Wyandot County, produced remains of at least 39 individual peccaries.
Cervalces scotti, sometimes called the stag-moose or elk-moose, is known from several specimens from Ohio. A nearly complete specimen was collected in Stark County and is on display at the Ohio Historical Society. These animals were similar in size and characteristics to the modern moose but their antlers differed.
Two species of musk ox lived in Ohio during the Ice Age, although fossils of either species are uncommon. Bootherium bombifrons is an extinct species. Ovibos moschatus still survives in northern climates.
One specimen of the giant-horned bison, Bison latifrons, is known from southwestern Ohio. The horns of this specimen measure about six feet from tip to tip. Specimens of modern bison, Bison bison, have been reported from presumed Pleistocene deposits.
Specimens of deer (Odocoileus virginianus), caribou (Rangifer tarandus), and elk (Cervus elaphus). Have been found in deposits that are late Pleistocene or early Holocene. Two fairly complete elk skeletons from Ohio have been radiocarbon dated to about 9,000 years old, suggesting that elk, which survived in Ohio until historic times, may have been an early migrant into the state after extinction of the megafauna.
Fossil remains of large carnivores are generally less common than remains of herbivores because of lesser abundance of the predators. Fragmentary remains of the short-faced bear, Arctodus simus, were found at Indian Trail Caverns and a skull of a grizzly bear, Ursus arctos, was found in Butler County. So far, fossils of the saber-toothed cat, Smilodon fatalis, and dire wolf, Canis dirus, have not been found in Ohio but it is likely that both species lived here because their remains have been found in nearby states. The small number of Pleistocene cave sites in Ohio probably accounts for lack of a fossil record of these animals in Ohio.
The giant beaver, Castoroides ohioensis, is comparatively well known from Ohio�s Pleistocene sediments, with 15 specimens recorded. This black-bear sized rodent looked similar to modern beaver, Castor canadensis, but was much larger. It has been suggested that giant beaver did not build dams or gnaw on trees, but fed on aquatic vegetation. The first known and described specimen of giant beaver (type specimen) was found near Nashport, Muskingum County, and was illustrated in 1838 by the first Geological Survey of Ohio. Specimens of giant beaver fossils are displayed at the Ohio Historical Society.
In addition to modern beaver, Pleistocene sediments in Ohio have produced remains of small mammals such as shrews, bats, red squirrel, tree squirrel, voles, and field mice. Medium-sized mammals include woodchuck, porcupine, muskrat, weasel, pine marten, fisher, mink, skunk, red fox, raccoon, and river otter. Most of these remains have come from cave or bog sites that have been systematically excavated.