Vertebrate subclasses

Theria ( or ; ) is a subclass of mammals amongst the Theriiformes. Theria contains the eutherians (which includes placental mammals) and the metatherians (which includes marsupials) but excludes the egg-laying monotremes and various extinct mammals evolving prior to the common ancestor of placentals and marsupials.

Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including modern sharks (division Selachii), and batomorphs (division Batomorphi, including rays, skates, and sawfish). Members of this subclass are characterised by having five to seven pairs of gill slits opening individually to the exterior, rigid dorsal fins and small placoid scales on the skin. The teeth are in several series; the upper jaw is not fused to the cranium, and the lower jaw is articulated with the upper. The details of this jaw anatomy vary between species, and help distinguish the different elasmobranch

Holocephali (sometimes spelled Holocephala; Greek for "complete head" in reference to the fusion of upper jaw with the skull) is a subclass of cartilaginous fish. The only living holocephalans are the three families of chimaeras, but the group also includes many extinct members and was more diverse during the Paleozoic and Mesozoic eras. The earliest known fossils of holocephalans date to the Middle Devonian, and the subclass likely reached its peak diversity during the following Carboniferous Period. Molecular clock studies suggest that holocephalans diverged from their closest relatives, ela

Rhipidistia, also known as Dipnotetrapodomorpha, is a clade of lobe-finned fishes which includes the tetrapods and lungfishes. Rhipidistia formerly referred to a subgroup of Sarcopterygii consisting of the Porolepiformes and Osteolepiformes, a definition that is now obsolete. However, as cladistic understanding of the vertebrates has improved over the last few decades, a monophyletic Rhipidistia is now understood to include the whole of Tetrapoda and the lungfishes.

thumb|254px|right|Among the most primitive heterostracans are Tolypelepidida|tolypelepids (top right). Most heterostracans are pteraspidiforms, such as the pteraspidids (bottom right), doryaspidids (bottom left) and the huge psammosteids (top left), which are the youngest known members of the group.

Cladistia is a subclass of bony fishes whose only living members are the bichirs of tropical Africa. Their major synapomorphies are a dorsal fin with independent rays, and a posteriorly elongated parasphenoid.

300px|thumb|Painting of Archaeopteryx by [[Heinrich Harder, from around 1916]] The Archaeornithes, classically Archæornithes, is an extinct group of the first primitive, reptile-like birds. It is an evolutionary grade of transitional fossils, the primitive birds halfway between non-avian dinosaur ancestors and the derived modern birds (avian dinosaur).

Odontornithes is an obsolete and disused taxonomic term proposed by Othniel Charles Marsh for birds possessing teeth, notably the genera Hesperornis and Ichthyornis from the Cretaceous deposits of Kansas.

Yinotheria is a proposed basal subclass clade of crown mammals uniting the Shuotheriidae, an extinct group of mammals from the Jurassic of Eurasia, with Australosphenida, a group of mammals known from the Jurassic to Cretaceous of Gondwana, which possibly include living monotremes. Today, there are only five surviving species of monotremes which live in Australia and New Guinea, consisting of the platypus and four species of echidna. Fossils of yinotheres have been found in Britain, China, Russia, Madagascar and Argentina. Contrary to other known crown mammals, they retained postdentary bones

thumb|left|Sacabambaspis, the best known arandaspid, from the Ordovician of Bolivia. Shows the characteristic, frontally positioned eyes, like car head lamps Arandaspida is a taxon of very early, jawless prehistoric fish which lived during the Ordovician period. Arandaspids represent some of the oldest known vertebrates. The group represents a subclass within the class Pteraspidomorphi, and contains only one order, the Arandaspidiformes. The oldest known genus of this group is Sacabambaspis found in South America.