Mammals can be generally classified into three broad groups: egg-laying monotremes, marsupials, and placentals. A marsupial is a mammal that raises its newborn offspring inside an external pouch at the front or underside of their bodies. In contrast, a placental is a mammal that completes embryo development inside the mother, nourished by an organ called the placenta. Both marsupial and placental mammal groups give birth to live young. Each animal in an ecosystem occupies a specific position. Niche is the word used to describe the specific role that an organism (or a population) fills in a specific environment, including the resources it uses and its competitors for those resources.

Placental mammals account for the majority of modern mammal species alive today. Most extant marsupials can be found in Australia and South America although the fossil record shows that they were once more widespread.

SF Table 1.1. Marsupial mammals

Marsupial Mammal	Niche	Photo of Mammal
Kangaroo	Large herbivore that forages extensively across open grasslands
Wombat	Medium-sized diurnal herbivore that feeds on grasses, constructs and dwells in extensive tunnel systems
Thylacine	Large, nocturnal fast moving predator that feeds on other mammals
Tasmanian Devil	Stocky nocturnal omnivore that primarily scavenges carrion and feeds on insects and plants
Bandicoot	Small foraging omnivore that eats insects and plants, small rodents, and lizards
Quoll	Small nocturnal carnivore that is an aggressive predator on small mammals, insects, and reptiles
Numbat	Diurnal insectivore that uses a specialized tongue to feed on ants and termites found in decaying wood
Dunnart	Small, nocturnal burrowing insectivore that builds nests of grass and plant material in dry areas

SF Table 1.2. Placental mammals

Placental Mammal	Niche	Photo of Mammal
Antelope	Large herbivore that forages extensively across open grasslands
Groundhog	Medium-sized diurnal herbivore that feeds on grasses, constructs and dwells in extensive tunnel systems
Wolf	Large, nocturnal fast moving predator that feeds on other mammals
Raccoon	Stocky nocturnal omnivore that primarily scavenges carrion, and feeds on insects and plants
Hedgehog	Small foraging omnivore that eats insects, plants, small rodents, and lizards
Weasel	Small nocturnal carnivore that is an aggressive predator on small mammals, insects, and reptiles
Anteater	Diurnal insectivore that uses a specialized tongue to feed on ants and termites found in decaying wood
Mouse	Small, nocturnal burrowing insectivore that builds nests of grass and plant material in dry areas