No classification system is universally accepted; Mc Kenna & Bell (1997) and Wilson & Reader (2005) provide useful recent compendiums.
George Gaylord Simpson's "Principles of Classification and a Classification of Mammals" (AMNH Bulletin v.
The early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that produced the non-mammalian Dimetrodon.
At the end of the Carboniferous period, this group diverged from the sauropsid line that led to today's reptiles and birds.
The largest group of mammals, the placentals, have a placenta, which enables the feeding of the fetus during gestation.
Mammals range in size from the 30–40 mm (1.2–1.6 in) bumblebee bat to the 30-meter (98 ft) blue whale.
Mammals include the largest animal on the planet, the blue whale.
They provided, and continue to provide, power for transport and agriculture, as well as various commodities such as meat, dairy products, wool, and leather.
Most mammals are intelligent, with some possessing large brains, self-awareness and tool use.
Mammals can communicate and vocalize in several different ways, including the production of ultrasound, scent-marking, alarm signals, singing, and echolocation.
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.
Findings from molecular genetics, for example, have prompted adopting new groups, such as the Afrotheria, and abandoning traditional groups, such as the Insectivora.