Eutherian mammals are also called placental mammals. Included in this infraclass are dogs, cats, bears, whales, monkeys, humans, etc. The term is also frequently used to refer to the appearance of a new species. More specifically, it is change in the gene pool frequencies of a population from one generation to the next. In the Linnaean classification system, genus is the category immediately above species .
Pregnancy is another word for gestation.
Mammals are heterodonts. Lower down are levels of less inclusive sub-categories. The lowest sub-category is a species. Homologies are also referred to as homologous structures. Homoplasies are also referred to as homoplastic structures .