Cross references: Therapsids Reptiles Amphibians Lungfish
Permian Discontinuity Subcortical Brain
class Mammalia ( //), air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young. "
"Synapsida, the group which contains mammals and their extinct relatives, originated during the Pennsylvanian subperiod, when they split from the lineage that led to reptiles and birds. "
"The first fully terrestrial vertebrates were amniotes. Like their amphibian predecessors, they have lungs and limbs. Amniotes' eggs, however, have internal membranes which allow the developing embryo to breathe but keep water in. Hence, amniotes can lay eggs on dry land, while amphibians generally need to lay their eggs in water. The first amniotes apparently arose in the Late Carboniferous. They descended from earlier reptiliomorph amphibians, which lived on land already inhabited by insects and other invertebrates, and by ferns, mosses and other plants. Within a few million years, two important amniote lineages became distinct: the synapsids, which include mammals; and the sauropsids, which include turtles, lizards, snakes, crocodilians, dinosaurs and birds. "
"One synapsid group, the pelycosaurs, included the largest and fiercest animals of the early Permian. Therapsids descended from pelycosaurs in the middle Permian, about 265 million years ago, and took over their position as the dominant land vertebrates. "
"The therapsid lineage leading to mammals went through a series of stages, beginning with animals that were very like their pelycosaur ancestors and ending with probainognathian cynodonts, some of which could easily be mistaken for mammals"
"The Permian–Triassic extinction event, which was a prolonged event due to the accumulation of several extinction pulses, ended the dominance of the carnivores among the therapsids. "
"The first mammals (in the sense given to the term by Kielan-Jawarowska et al.) appeared in the Late Triassic epoch (about 210 million years ago), 60 million years after the first therapsids."
"All mammalian brains possess a neocortex, a brain region unique to mammals. Placental mammals have a corpus callosum, unlike monotremes and marsupials. The size and number of cortical areas (Brodmann's areas) is least in monotremes (about 8-10) and most in placentals (up to 50)."
"The early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that also included Dimetrodon. At the end of the Carboniferous period, this group diverged from the sauropsid line that led to today's reptiles and birds. Preceded by many diverse groups of non-mammalian synapsids (sometimes referred to as mammal-like reptiles), the first mammals appeared in the early Mesozoic era. The modern mammalian orders arose in the Paleogene and Neogene periods of the Cenozoic era."