Characteristics

Mammals have three different characteristics that other creatures don’t have. One is hair. At some point in their life mammals have hair. Did you know that whales and dolphins have sensitive bristles on their snouts, considered as hair? Hair can be an insulation to keep a warm body temperature. This enables them to go in just about any climate. It also gives a color pattern and a sense of touch. If you have ever touched a cat or dog you would know how soft their hair is. Another characteristic is that all females have mammary glands. Mammary glands produce milk. This is so that mothers can feed their young with milk since the young can’t have actual food until they’re older. The third characteristic is that all mammals have 3 middle ear bones. Mammals also have teeth, a lower jaw, and a well developed brain.

There are about 5000 species of mammals in the world. Each of them are in one of 26 orders. The smallest mammals on earth are shrews and bats, weighing as little as three grams. The largest mammals on earth are blue whales. They weigh as much as 160,000 kg. If mammals are small they’ll have a short life but if they are large they’ll have a long life. Mammals can be found on any continent, oceanic island, and ocean. Each species has its own habitat and temperature that suits it. They are also warm-blooded animals. They are nocturnal, diurnal, or crepuscular. These determine which part of the day the mammals are awake or asleep.

History

The first mammals appeared on earth 220 million years ago in the Mid-Triassic period. Scientist have a theory that placental mammals arose in Gondwana. 155 million years ago mammals were only insectivores and herbivores and they all fit into five orders. None of them were carnivores. Scientists are still learning about mammals and are figuring out new things each day.

Breeding

Most mammals are polygynous or promiscuous. Polygynous means that males will mate with multiple female. Promiscuous means males and females will mate with multiple mates in a given reproductive season. Only 3 percent of mammals are monogamous which means males will mate with one female each season and some of the males will take care of the offspring. In order to attract a mate mammals will behave in complex ways. One behavior is males will have male on male competition between species and the winner will end up winning the females heart. Most mammals are placental which means they interact through an organ that connects the embryo and the uterus. Other mammals are either monotremes or marsupials. Monotremes lay eggs in a primitive reproductive condition while marsupials have young that are born at an early stage. The young of marsupials spend a long amount of time nursing since they attach onto the mother’s nipples and stay there while they develop. The young of all mammals depend on their mothers for milk. Males will care for the young depending on resources. If the resources are low males will mate with one female and care for young but if the resources are high the mother will care for young and the male will attempt to have offspring with multiple female. Some mammals prefer to be alone (solitary) while other mammals prefer to be in groups or herds.

Predators and prey

Mammals eat many different things. Some will eat plants and others will eat meat. When they eat meat they’re considered carnivores but when they eat plants they’re considered herbivores. Some mammals, like humans, will eat both plants and meat and that’s called omnivore. Mammals have many tricks for avoiding predators. Some give off defensive chemicals while others have protective armor or physical defense. Some can even use camouflage to match the color of they’re surroundings.

Mammals in the Connecticut River Valley Watershed: Black Bear, Bobcat, Eastern Coyote, Flying Squirrel, Little Brown Bat, American Marten, Moose, Meadow Vole, River Otter

Resources:

Wund,M. and P. Myers, 2005, "Mammalia" (online), Animal Diversity Web, Acessed March 31,2007 at http://animaldiversity.ummz.umich.edu/site/accounts/information/mammalia.html

Raven, Poter H. and Johnson, Goerge B. Biology Sixth Edition. New York, NY: McGraw- Hill Companies Ina 2002