Nicholas dagosto is dating
Mammals are hunted or raced for sport, and are used as model organisms in science.
Mammals have been depicted in art since Palaeolithic times, and appear in literature, film, mythology, and religion.
In some classifications, extant mammals are divided into two subclasses: the Prototheria, that is, the order Monotremata; and the Theria, or the infraclasses Metatheria and Eutheria.
The marsupials constitute the crown group of the Metatheria, and include all living metatherians as well as many extinct ones; the placentals are the crown group of the Eutheria.
Living mammals are divided into the Yinotheria (platypus and echidnas) and Theriiformes (all other mammals).
There are around 5450 species of mammal, depending on which authority is cited.
While mammal classification at the family level has been relatively stable, several contending classifications regarding the higher levels—subclass, infraclass and order, especially of the marsupials—appear in contemporaneous literature.
At the end of the Carboniferous period, this group diverged from the sauropsid line that led to today's reptiles and birds.85, 1945) provides systematics of mammal origins and relationships that were universally taught until the end of the 20th century.Since Simpson's classification, the paleontological record has been recalibrated, and the intervening years have seen much debate and progress concerning the theoretical underpinnings of systematization itself, partly through the new concept of cladistics.Mammals can organize themselves into fission-fusion societies, harems, and hierarchies, but can also be solitary and territorial.Most mammals are polygynous, but some can be monogamous or polyandrous.