Mastodon

The mastodon, an elephantikle mammal belonging to the order Proboscidea, was widespread from Miocene through the Pleistocene epochs (26 million to 10 thousand years ago). Mastodons were in the mainline of proboscidean evolution, first appearing in the early Oligocene (38 million to 26 million years ago). Their teeth, consisting of a series of paired conical cusps, seen in profile resemble a woman’s breasts; hence the name mastodon was derived from the Greek for breasts tooth.

Gomphotherium (also called Trilophodon) lived during the late Miocene and the early Pliocene (12 million to 3, 5 million years ago). It resemble Phiomia, but the teeth were more beastlike and the trunk was more fully developed. Shovel-tusked mastodons such as amebelodon developed broad, scoop-shaped lower tusks that were useful for digging vegetation. Mastodon americanus, common in North America during the Pleistocene Epoch and perhaps up to a few thousand years ago, was not as tall as tall as modern elephants. Its strongly curved upper tusks were very large, and its body was covered with long, reddish brown hair.


The Mastodon, a browsing mammal somewhat smaller than a present day elephant became extinct only in the last 10,000 years.

Muskrat

The muskrat, Ondatra zibethicus, in the family Cricetidae, is a semiaquatic rodent found in fresh-water and saltwater marshes from Alaska through most of Canada and the United States. It was introduced into Europe for its fur but quickly became a pest. A dark colored polulation in Newfoundland is often classified as a separate species. O. obscurus. Muskrats are stoutly built, reaching about 33 cm (13 in) long, plus a laterally flattened 29 cm (11-in) tail, and they weigh up to 1.8 kg (4 lb). The hind feet are partly webbed. The dense, glossy coat ranges in color from grayish brown to dark brown or almost black. Muskrats live in a network of burrows in the banks of waterways or build houses of mounded vegetation in open water. They eat mainly plant material. Breeding is confined to the warmer moths in the north, where a female may have three litters a year, but occurs year round in the south. Gestation takes about 30 days, with usually three to seven young to a litter. The musk rat’s fur is of prime commercial importance.

The muskrat dives and swims in the freshwater habitat by padding with partially webbed hind feet. It builds a shelter in the water or burrows into the sides of earthen banks.

Otter

Otters are long bodied, semi aquatic members of the weasel family, Mustelidae. This group includes the sea otter, genus Enhydra, the river otters, Lutra; the giant otter, Pteronura, of South America; the African clawless otter, Aonyx; and the small clawed otters of Asia, Amblonyx and Africa, Paronyx, both of which are often classified with the clawless otter.

The river otters, Lutra, comprise 11 or 12 species found on all the continents except Australia and Antartica and include the North America otter, L. Canadensis, and European otter, L. lutra. They have broad snouths, small ears, short legs with fully webbed, and a thick but tapering tail. Their underfur is short and dense, brownish or grayish in color, and is overlain with darker, coarser guard hairs. Male river otters reach about 1 m (3 ft) in length, plus a 50 cm (19 in) tail; they weigh up to about 14 kg (30 lb). Females are smaller.

River Otters feed and small land mammals. Northern populations of river otters mate in summer, and the young are not born until 91/2 to 121/2 months later. This prolonged gestation is due to the delayed implantation, or attachment, of the newly developing embryo to the wall of the uterus.