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**Evolution and Classification**:
– Mammals originated from cynodonts during the Late Triassic to Early Jurassic.
– Modern mammalian diversity was achieved in the Paleogene and Neogene periods.
– Mammals have undergone classifications by various scientists like Carl Linnaeus and Simpson.
– The McKenna/Bell classification system revised mammal taxonomy in 1997.
– Molecular studies have challenged and reshaped the understanding of mammal relationships.

**Anatomical Features**:
– Mammals can be identified by sweat and milk-producing glands.
– Distinguishing features like jaw joint and middle ear characterize mammals.
– Tooth replacement patterns vary from diphyodonty to continuous growth.
– Unique anatomical features like neocortex in the brain and corpus callosum in placental brains set mammals apart.
– Soft tissue glands and other internal features aid in classification but are not visible in fossils.

**Role in Human Society**:
– Domestication of mammals played a significant role in the Neolithic Revolution.
– Mammals are utilized for transport, agriculture, fur, leather, and as working animals.
– They are hunted, kept as pets, used in scientific research, and for entertainment like racing.
– Human activities like poaching and habitat destruction are leading causes of mammal decline and extinction.
– The relationship between humans and mammals has been integral to societal development.

**Evolutionary History**:
– Mammals evolved from synapsids, distinct from sauropsids, during the Pennsylvanian subperiod.
– The first mammals appeared in the Late Triassic epoch, evolving from cynodonts.
– Various stages led to the development of unique mammalian features over time.
– The McKenna/Bell classification system reflects the historical genealogy of Mammalia.
– Estimates for divergence times among placental groups range from 105 to 120 million years ago.

**Physiological Systems**:
– Mammals have a four-chambered heart with four valves for efficient circulation.
– Breathing is facilitated by spongy, honeycombed lungs and the diaphragm.
– The integumentary system consists of epidermis, dermis, and hypodermis layers, with hair as a defining feature.
– Mammalian brains possess a neocortex, unique to mammals.
– Biological systems like the cervical vertebrae count and brain structures are consistent across most mammal species.

Mammal (Wikipedia)

A mammal (from Latin mamma 'breast') is a vertebrate animal of the class Mammalia (/məˈmli.ə/). Mammals are characterized by the presence of milk-producing mammary glands for feeding their young, a neocortex region of the brain, fur or hair, and three middle ear bones. These characteristics distinguish them from reptiles and birds, from which their ancestors diverged in the Carboniferous Period over 300 million years ago. Around 6,400 extant species of mammals have been described and divided into 29 orders.

Temporal range: Late Triassic – Recent; 225 or 167–0 Ma See discussion of dates in text
Common vampire batTasmanian devilFox squirrelPlatypusHumpback whaleGiant armadilloVirginia opossumHumanTree pangolinColugoStar nosed molePlains zebraEastern grey kangarooNorthern elephant sealAfrican elephantElkGiant pandaBlack and rufous elephant shrew
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Amniota
Clade: Synapsida
Clade: Mammaliaformes
Class: Mammalia
Linnaeus, 1758
Living subgroups

The largest orders of mammals, by number of species, are the rodents, bats, and Eulipotyphla (including hedgehogs, moles and shrews). The next three are the primates (including humans, monkeys and lemurs), the even-toed ungulates (including pigs, camels, and whales), and the Carnivora (including cats, dogs, and seals).

Mammals are the only living members of Synapsida; this clade, together with Sauropsida (reptiles and birds), constitutes the larger Amniota clade. Early synapsids are referred to as "pelycosaurs". The more advanced therapsids became dominant during the Middle Permian. Mammals originated from cynodonts, an advanced group of therapsids, during the Late Triassic to Early Jurassic. Modern mammalian achieved their modern diversity in the Paleogene and Neogene periods of the Cenozoic era, after the extinction of non-avian dinosaurs, and have been the dominant terrestrial animal group from 66 million years ago to the present.

The basic mammalian body type is quadruped, and most mammals use their four extremities for terrestrial locomotion; but in some, the extremities are adapted for life at sea, in the air, in trees, underground, or on two legs. Mammals range in size from the 30–40 mm (1.2–1.6 in) bumblebee bat to the 30 m (98 ft) blue whale—possibly the largest animal to have ever lived. Maximum lifespan varies from two years for the shrew to 211 years for the bowhead whale. All modern mammals give birth to live young, except the five species of monotremes, which are egg-laying mammals. The most species-rich group of mammals, the infraclass called placentals, have a placenta, which enables the feeding of the fetus during gestation.

Most mammals are intelligent, with some possessing large brains, self-awareness, and tool use. Mammals can communicate and vocalize in several ways, including the production of ultrasound, scent-marking, alarm signals, singing, echolocation; and, in the case of humans, complex language. 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.

Domestication of many types of mammals by humans played a major role in the Neolithic Revolution, and resulted in farming replacing hunting and gathering as the primary source of food for humans. This led to a major restructuring of human societies from nomadic to sedentary, with more co-operation among larger and larger groups, and ultimately the development of the first civilizations. Domesticated mammals provided, and continue to provide, power for transport and agriculture, as well as food (meat and dairy products), fur, and leather. Mammals are also hunted and raced for sport, kept as pets and working animals of various types, and are used as model organisms in science. Mammals have been depicted in art since Paleolithic times, and appear in literature, film, mythology, and religion. Decline in numbers and extinction of many mammals is primarily driven by human poaching and habitat destruction, primarily deforestation.

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