MAMMALS
Mammals are a class of animals whose members are characterized by the presence of mammalian characteristics. These include features such as mammary glands, which produce milk for nursing young; hair, which provides insulation; and three middle ear bones. The earliest mammals appeared during the Mesozoic Era (252 to 66 million years ago), although they may have evolved earlier from reptilian ancestors. The major groups of mammals are listed below, along with some notable representatives.
Subclass Prototheria
* Order Monotremata: platypus and echidnas
Subclass Metatheria
* Infraorder Dasyuromorphia: antechinus, numbat, quoll, Tasmanian devil
* Infraorder Peramelemorphia: bilby and bandicoots
* Infraorder Notoryctemorphia: marsupial moles
* Infraorder Diprotodontia: koala, kangaroo, wallaby, wombats Subclass Eutheria or placental mammals
Superorder Afrotheria Includes the following orders: Tubulidentata (aardvark) Hyracoidea (hyraxes) Sirenia (manatees and dugongs) Proboscidea (elephants) Paenungulata (elephant shrews, aardwolves, tenrecs) Superorder Xenarthra Includes the following order: Edentata or Xenarthra (anteaters, sloths, armadillos) Superorder Laurasiatheria Includes the following orders: Chiroptera (bats) Carnivora (dogs, cats, bears, weasels) Perissodactyla (horses , tapirs , rhinoceroses ) Artiodactyla (( pigs , hippopotamuses , camels , deer , cattle , sheep , goats )) Cetartiodactyla or Ungulata (( whales , dolphins , porpoises )) Lagomorpha (( hares , rabbits )) Macroscelidea (( elephant shrews )) Scandentia (( tree shrews )) Dermoptera (( colugos or flying lemurs )) Primates (( apes , monkeys , lemurs , lorises )) Rodentia (( mice rats squirrels beavers porcupines )); also includes lagomorphs
Mammals first appeared on Earth during the late Triassic period around 252 million years ago. They were small creatures that resembled modern-day rodents and were probably insectivores. The first true mammals appeared during the Jurassic period around 200 million years ago. These early mammals were small rodent-like animals known as multituberculates. By the end of the Jurassic period dinosaurs dominated both land and sea but early mammals managed to find niches in which to survive. Around 65 million years ago a massive meteorite hit Earth causing widespread devastation including mass extinctions among both plants and animals. Among those killed off were all dinosaurs except for a few birds which survived to give rise to all modern birds. This event created opportunities for small mammal species to radiation into many new ecological roles vacated by dinosaurs including some large herbivore roles previously occupied by reptiles such as crocodiles . One group of these successful early mammals was known as placentals which gave rise to all modern placental mammal groups while another group was known as marsupials which gave rise to all modern marsupial mammal groups including kangaroos possums opossums Koalas Wombats Bandicoots Numbats Quolls Bilbies Antechinus Tasmanian Devils Marsupial Moles . Placental mammals are distinguished from other mammal groups by their mode of reproduction in which a fertilized egg develops inside the female’s body until it is born live rather than hatching from an egg laid outside her body like most other animals . This allows time for more development in utero resulting in larger more complex newborns . Additionally maternal blood supply oxygenation and nutrients reach developing fetuses through an organ called the placenta . Marsupials have a similar but less well-developed structure called