Everything about Therapsid totally explained
Early
Permian -
Early Cretaceous (non-mammalian)
| image = Pristeroognathus DB.jpg
| image_width = 240 px
| image_caption = Illustration of
Pristerognathus, a
therocephalian therapsid
| regnum =
Animalia
| phylum =
Chordata
| subphylum =
Vertebrata
| superclassis =
Tetrapoda
| classis =
Synapsida
| ordo =
Therapsida *
| ordo_authority =
Broom, 1905
| subdivision_ranks = Clades
| subdivision =
Characteristics
Therapsids'
temporal fenestrae were larger than those of the pelycosaurs. The jaws of therapsids were more complex and powerful and the
teeth were differentiated into frontal
incisors for nipping, large lateral
canines for puncturing and tearing, and
molars for shearing and chopping food. Therapsids' legs were positioned more vertically beneath their bodies than were the sprawling legs of
reptiles and
pelycosaurs.
Evolutionary history
The Therapsids'
evolutionary track began in the Early Permian, when a group of
pelycosaurs, the
Sphenacodontia, a lineage that included
Dimetrodon and
its relatives, gave rise to therapsids. Evidence was their anatomical features such as the
skull, and the
vertebrae. Therapsids became the dominant land animals in the Middle
Permian, replacing the pelycosaurs who were becoming rare as Permian period progressed. Therapsida consists of three major
clades, the
dinocephalians, the herbivorous
anomodonts and the mostly carnivorous theriodonts, with the carnivorous
biarmosuchians as a
paraphyletic assemblage of primitive forms. After a brief burst of evolutionary diversity, the dinocephalians died out in the later Middle Permian (
Guadalupian) but the anomodont
dicynodonts and the theriodont
gorgonopsians and
therocephalians flourished, being joined at the very end of the Permian by the first
cynodonts.
Like all land animals, the therapsids were seriously affected by the
Permian–Triassic extinction event, with the very successful gorgonopsians dying out altogether and the remaining groups,
dicynodonts,
therocephalians and
cynodonts of a few species, each surviving into the
Triassic. The dicynodonts, now represented by a single family of large stocky
herbivores, the
Kannemeyeridae, and the medium-sized cynodonts (including both carnivorous and herbivorous forms), flourished worldwide, throughout the Early and Middle Triassic. They died out across much of
Pangea at the end of the
Carnian (Late Triassic), although they continued for some time longer in the wet equatorial band and the south.
Some exceptions were the still further derived
eucynodonts. At least three groups of them survived. They all appeared in the
Late Triassic epoch.
The extremely mammal-like family, Tritylodontidae, survived into the Early Cretaceous.
An extremely mammal-like family, Tritheledontidae, are unknown later than the Early Jurassic.
The third group, Morganucodon and similar animals, were mammaliformes or the "stem-mammals".
Some non-eucynodont cynodonts survived the Permian-Triassic extinction, such as Thrinaxodon but only to become extinct by the Middle Triassic.
The therocephalians, relatives of the cynodonts, managed to survive the Permian-Triassic extinction and continued to diversify through Early Triassic epoch. Approaching the end of the epoch, however, the therocephalians were declining to extinction and eventually became extinct, possibly due to climatic changes and competition from cynodonts and other animals struggling to survive.
Dicynodonts are thought to have become extinct before the end of the Triassic, but there's evidence that they survived the extinction. Their fossils have been found in Gondwana. Other animals that were common in the Triassic also took refuge here, such as the Temnospondyls. This is an example of Lazarus taxon.
Mammals, the only living therapsids, evolved in the Early Jurassic epoch. They radiated from a group of mammaliaformes that's related to the symmetrodonts. The mammaliaformes themselves evolved from probainognathians, a lineage of the eucynodont suborder.
Taxonomy
Classification
Class Synapsida
ORDER THERAPSIDA *
