how do define a mammal?

Answer 1

The mammals are the class of vertebrate animals characterized by the presence of mammary glands, which in females produce milk for the nourishment of young; the presence of hair or fur; specialized teeth; the presence of a neocortex region in the brain; and endothermic or "warm-blooded" bodies. The brain regulates endothermic and circulatory systems, including a four-chambered heart. Mammals encompass some 5,500 species (including Humans), distributed in about 1,200 genera, 152 families and up to 46 orders, though this varies with the classification scheme.

Phylogenetically, Mammalia is defined as all descendants of the most recent common ancestor of monotremes (e.g., echidnas and platypuses) and therian mammals (marsupials and placentals).

Answer 2

There are several characters which distinguish mammals from other groups. The big three are:

1 - Three inner ear bones (ossicles)
2 - Mammary glands which produce milk to feed young
3 - Pelage consisting of keratinous hair

If a critter has those characters, it's a mammal. If it doesn't have those characters, it's not.

Answer 3

I think a mammal is any animal that makes milk for its young.

Answer 4

Symmetry is the prime indicator among all animals. Whether it is the arbitrary or " good genes " function of sexual selection. Symmetry indicates an organism free of developmental insults, among other things. This is why you can judge other animals as beautiful. Despite what the relativists, Oprah, Dove soap and some feminists, say about beauty. PS Sometimes it can appear arbitrary; think peacocks tail. PPS Start with Darwin's sexual selection theory.

Answer 5

The vertebrates who reproduce by giving birth, feed the young ones with their milk and the body is covered with hairs.

Answer 6

This terms refers to any vertebraes which their females have milk bearing organs to nourish their young.

Answer 7

www.wikipedia.org

^^^^^^^Great website.