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Therapsids are an order
Order (biology)

In Biological classification used in biology, the order is a taxonomic rank between class and family . The superorder is a rank between class and order....
 of synapsid
Synapsid

Synapsids , also known as theropsids , are a class of animals that includes mammals and everything closer to mammals than to other living amniotes....
s (Class Synapsida),and are believed to include mammals and their immediate evolutionary ancestors. Other than the mammals, all lineages of the therapsids are extinct
Extinction

In biology and ecology, extinction is the death of every member of a species or group of taxon. The moment of extinction is generally considered to be the death of the last individual of that species ....
, with the last known non-mammalian therapsids dying out in the Early Cretaceous
Early Cretaceous

The Early Cretaceous or the Lower Cretaceous , is the earlier of the two major divisions of the Cretaceous Period . It began about 146 million years ago....
 period.

apsids' temporal fenestrae were larger than those of the pelycosaurs.






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Therapsids are an order
Order (biology)

In Biological classification used in biology, the order is a taxonomic rank between class and family . The superorder is a rank between class and order....
 of synapsid
Synapsid

Synapsids , also known as theropsids , are a class of animals that includes mammals and everything closer to mammals than to other living amniotes....
s (Class Synapsida),and are believed to include mammals and their immediate evolutionary ancestors. Other than the mammals, all lineages of the therapsids are extinct
Extinction

In biology and ecology, extinction is the death of every member of a species or group of taxon. The moment of extinction is generally considered to be the death of the last individual of that species ....
, with the last known non-mammalian therapsids dying out in the Early Cretaceous
Early Cretaceous

The Early Cretaceous or the Lower Cretaceous , is the earlier of the two major divisions of the Cretaceous Period . It began about 146 million years ago....
 period.

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 incisor
Incisor

Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below....
s for nipping, large lateral canines
Canine tooth

In mammalian oral anatomy, the canine teeth, also called cuspids, dogteeth, fangs, or eye teeth, are relatively long, pointed tooth....
 for puncturing and tearing, and molar
Molar (tooth)

Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....
s for shearing and chopping food. Therapsids' legs were positioned more vertically beneath their bodies than were the sprawling legs of reptile
Reptile

Reptiles, or members of the class Reptilia, are air-breathing, cold-blooded vertebrates that have skin covered in scale as opposed to hair or feathers....
s and pelycosaur
Pelycosaur

The pelycosaurs were primitive Late Paleozoic synapsid amniotes. Some species were quite large and could grow up to 3 meters or more, although most species were much smaller....
s.

Evolutionary history

The therapsids' evolution
Evolution

In biology, evolution is change in the heritability trait of a population of organisms from one generation to the next. These changes are caused by a combination of three main processes: variation, reproduction, and selection....
ary track began in the Early Permian, when a group of pelycosaur
Pelycosaur

The pelycosaurs were primitive Late Paleozoic synapsid amniotes. Some species were quite large and could grow up to 3 meters or more, although most species were much smaller....
s, the Sphenacodontia
Sphenacodontia

Sphenacodontia is the name given to the clade that includes the Sphenacodontidae and all their descendants . They first appear during the Late Pennsylvanian epoch....
, a lineage that included Dimetrodon
Dimetrodon

Dimetrodon was a predatory synapsid genus that flourished during the Permian Period , living between 280?265 million years ago. It was more closely related to mammals than to true reptiles such as lizards....
 and its relatives
Sphenacodontidae

The Sphenacodontidae are a family of small to large, advanced, carnivore, Late Pennsylvanian to Guadalupian pelycosaurs. Primitive forms were generally small in size , but during the later part of the early Permian these animals grew progressively larger , to become the Apex predator of their environments....
, gave rise to therapsids. Evidence was their anatomical features such as the skull
Skull

The skull is a bone structure found in the head of many animals. The skull supports the structures of the face and protects the head against injury....
, and the vertebra
Vertebra

A vertebra is an individual bone in the flexible column that defines vertebrate animals. The vertebral column encases and protects the spinal cord, which runs from the base of the cranium down the dorsal side of the animal until reaching the pelvis....
e. Therapsids became the dominant land animals in the Middle Permian
Permian

The PermianThe term "Permian" was introduced into geology in 1841 by Sir Roderick Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian system" after the ancient kingdom...
, replacing the pelycosaurs who were becoming rare as Permian period progressed. Therapsida consists of three major clades, the dinocephalia
Dinocephalia

Dinocephalia are a cladistics of large early Therapsida that flourished during the Guadalupian, but became extinct leaving no descendants.Apart from the Biarmosuchia and the Eotitanosuchus olsoni, the Dinocephalia are the least advanced among the therapsids, although still uniquely specialised in their own way....
ns, the herbivorous anomodont
Anomodont

The Anomodontia are one of the three major groups of therapsids, an extinct group of animals commonly known as "mammal-like reptiles." They were mostly toothless herbivorous....
s and the mostly carnivorous theriodonts, with the carnivorous biarmosuchia
Biarmosuchia

The Biarmosuchia, also known as the Eotitanosuchia and the Phthinosuchia are an assemblage of primitive Permian Therapsida that represent either a paraphyletic stem group or a very early off-shoot of the main Therapsid tree....
ns 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 dicynodont
Dicynodont

The Dicynodontia are a taxon of Therapsids or mammal-like reptiles. Dicynodonts were small to large Herbivore animals with two tusks, hence their name, which means 'two dog tooth'....
s and the theriodont gorgonopsia
Gorgonopsia

Gorgonopsia is a suborder of therapsid synapsids. Their name is a reference to the Gorgons of Greek mythology. Like other therapsids, gorgonopsians were at one time called "mammal-like reptiles", though in most current classifcation systems, they are not true reptiles, but instead are much more closely related to true mammals....
ns and therocephalia
Therocephalia

Therocephalians are an extinct lineage of eutheriodont therapsids that lived throughout the middle and late Permian and into the Triassic. The therocephalians are named after their large skulls, which, along with their teeth, suggest that most were successful carnivores....
ns flourished, being joined at the very end of the Permian by the first cynodont
Cynodont

Cynodonts, or 'dog teeth', are a taxon of Therapsids which includes modern mammals and their extinct close relatives. They were one of the most diverse groups of therapsids....
s.

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, dicynodont
Dicynodont

The Dicynodontia are a taxon of Therapsids or mammal-like reptiles. Dicynodonts were small to large Herbivore animals with two tusks, hence their name, which means 'two dog tooth'....
s, therocephalia
Therocephalia

Therocephalians are an extinct lineage of eutheriodont therapsids that lived throughout the middle and late Permian and into the Triassic. The therocephalians are named after their large skulls, which, along with their teeth, suggest that most were successful carnivores....
ns and cynodont
Cynodont

Cynodonts, or 'dog teeth', are a taxon of Therapsids which includes modern mammals and their extinct close relatives. They were one of the most diverse groups of therapsids....
s of a few species, each surviving into the Triassic
Triassic

The Triassic is a geologic period that extends from about 251 to 199 annum . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic....
. The dicynodonts, now represented by a single family of large stocky herbivore
Herbivore

Herbivory is a form of predation in which an organism, known as an herbivore, heterotrophs principally autotrophs such as plants, algae and photosynthesizing bacteria....
s, 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
Carnian

The Carnian is the lowermost stage of the Upper Triassic series . Its boundaries are not characterized by major extinctions or biotic turnovers, but a climatic event occurred during the Carnian and seems to be associated with important extinctions or biotic radiations....
 (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
Late Triassic

The Late Triassic is in the geologic timescale the third and final of three epoch s of the Triassic geological timescale. The corresponding series is known as the Upper Triassic....
 period.
  1. The extremely mammal-like family, Tritylodontidae
    Tritylodontidae

    Tritylodontids were small to medium-sized, highly specialized and extremely mammal-like cynodonts. They were the last family of the non-mammalian synapsids....
    , survived into the Early Cretaceous
    Cretaceous

    The Cretaceous , usually abbreviated K for its German translation Kreide, is a geologic period from circa to million years ago . In the geologic timescale, the Cretaceous follows on the Jurassic period and is followed by the Paleogene period....
    .
  2. An extremely mammal-like family, Trithelodontidae
    Trithelodontidae

    The Trithelodontids, also known as Ictidosaurs, were small to medium-sized cynodonts. They were extremely mammal-like, highly specialized cynodonts, although they still retained a very few reptile anatomical traits....
    , are unknown later than the Early Jurassic
    Jurassic

    The Jurassic is a geologic period that extends from about annum to  Ma, that is, from the end of the Triassic to the beginning of the Cretaceous....
    .
  3. The third group, Morganucodon
    Morganucodon

    Morganucodon is an early mammalian genus which lived during the Upper Triassic. It first appeared about 205 million years ago. This has also been identified with Eozostrodon....
     and similar animals, were mammaliformes or the "stem-mammals".
Some non-eucynodont cynodonts survived the Permian-Triassic extinction, such as Thrinaxodon
Thrinaxodon

Thrinaxodon was a cynodont, a cat-sized therapsid. Pits on the skull indicate that Thrinaxodon had Vibrissae and, therefore probably also had a covering of fur....
 but only to become extinct by the Middle Triassic
Middle Triassic

The Middle Triassic is the second of three epoch s of the Triassic geological timescale. It spans the time between 245 ? 1.5 annum and 228 ? 2 Ma . The Middle Triassic is divided into the Anisian and Ladinian faunal stages....
.

The therocephalia
Therocephalia

Therocephalians are an extinct lineage of eutheriodont therapsids that lived throughout the middle and late Permian and into the Triassic. The therocephalians are named after their large skulls, which, along with their teeth, suggest that most were successful carnivores....
ns, relatives of the cynodonts, managed to survive the Permian-Triassic extinction and continued to diversify through the Early Triassic
Early Triassic

The Early Triassic is the first of three epoch s of the Triassic period . It spans the time between 251 ? 0.4 annum and 245 ? 1.5 Ma . The Permian-Triassic extinction event spawned the Triassic period....
 period. Approaching the end of the period, however, the therocephalians were declining to extinction and eventually became extinct, possibly due to climatic changes
Climate change

Climate change is any long-term significant change in the expected patterns of average weather of a specific region over an appropriately significant period of time....
 and competition from cynodonts and other animal
Animal

Animals are a major group of multicellular, eukaryotic organisms of the Kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life....
s struggling to survive.

Dicynodonts are thought to have become extinct before the end of the Triassic
Triassic-Jurassic extinction event

The Triassic?Jurassic extinction event marks the boundary between the Triassic and Jurassic periods, , and is one of the major extinction events of the Phanerozoic eon, profoundly affecting life on land and in the oceans....
, but there is evidence that they survived the extinction. Their fossils have been found in Gondwana
Gondwana

Gondwana , originally Gondwanaland is the name given to a southern precursor-supercontinent and then as a remnant separated from Laurasia 180- during the breakup of the Pangaea supercontinent that existed about 500 to 200 Annum ago into two large segments.. Other animals that were common in the Triassic also took refuge here, such as the Temnospondyls. This is an example of Lazarus taxon
Lazarus taxon

In paleontology, a Lazarus taxon is a taxon that disappears from one or more periods of the fossil record, only to appear again later. The term refers to the account in the Gospel of John chapter 11 in which Jesus miraculously raises Lazarus from the dead....
.

Mammal
Mammal

Mammals are a class of vertebrate animals whose name is derived from their distinctive feature, mammary glands, with which they feed their young....
s, the only living therapsids, evolved in the Early Jurassic
Early Jurassic

The Early Jurassic epoch is the earliest of three epochs of the Jurassic period. The Early Jurassic starts immediately after the Triassic-Jurassic extinction event and ends at the start of the Middle Jurassic ....
 period. They radiated from a group of mammaliaformes
Mammaliaformes

Mammaliaformes is a clade that contains the mammals and their closest Extinction relatives. The precise Phylogenetics is disputed due to the scantness of evidence in the fossil record....
 that is related to the symmetrodonts. The mammaliaformes themselves evolved from probainognathia
Probainognathia

The Probainognathians are a group of mostly carnivore cynodonts, and are one of the two main branches of the infraorder Eucynodontia, the other being the mainly herbivore Cynognathia....
ns, a lineage of the eucynodont suborder.

Paleocene Therapsid?

Chronoperates
Chronoperates

Chronoperates is a possible therapsida whose remains have been found in Alberta, Canada. It has also been suggested that it may be a Symmetrodonta....
 is a newly described genus of vertebrate that lived 55 million years ago
Paleocene

The Paleocene or Palaeocene, "early dawn of the recent" is a geologic epoch that lasted from 65.5 ? 0.3 Mega-annum to 55.8 ? 0.2 Ma . It is the first epoch of the Palaeogene Period in the modern Cenozoic era ....
. Its true identity is still debated and it has even been suggested that it is a symmetrodont
Symmetrodonta

Symmetrodonta is a basal group of Mesozoic mammals characterized by the triangular aspect of the Molar s when viewed from above and the absence of a well-developed talonid....
. Should it turn out to be a therapsid, the extinction date for this group would be pushed forward almost 45 million years.

Taxonomy


Classification

  • Class Synapsida
  • ORDER THERAPSIDA *
    Paraphyly

    In phylogenetics, a group of organisms is said to be paraphyletic if the group contains its most recent common ancestor Common descent but does not contain all the descendants of that ancestor....
    • Suborder Biarmosuchia
      Biarmosuchia

      The Biarmosuchia, also known as the Eotitanosuchia and the Phthinosuchia are an assemblage of primitive Permian Therapsida that represent either a paraphyletic stem group or a very early off-shoot of the main Therapsid tree....
       *
      Paraphyly

      In phylogenetics, a group of organisms is said to be paraphyletic if the group contains its most recent common ancestor Common descent but does not contain all the descendants of that ancestor....
      • Family Biarmosuchidae
        • Biarmosuchus
      • Family Eotitanosuchidae
        • Eotitanosuchus
    • Eutherapsida
      • Suborder Dinocephalia
        Dinocephalia

        Dinocephalia are a cladistics of large early Therapsida that flourished during the Guadalupian, but became extinct leaving no descendants.Apart from the Biarmosuchia and the Eotitanosuchus olsoni, the Dinocephalia are the least advanced among the therapsids, although still uniquely specialised in their own way....
        • Family Estemmenosuchidae
          Estemmenosuchidae

          Estemmenosuchidae are a Family of large, very early herbivore mammal-like reptiles that flourished during the Middle Permian period. They are distinguished by horn-like structures, probably for Animal communication or agonistic behavior....
          • Estemmenosuchus
            Estemmenosuchus

            Estemmenosuchus is a genus of large, early omnivore therapsid that lived during the middle part of the Middle Permian period. It was the largest animal of its day, and is characterised by distinctive horns-like structures, probably for intra-specific display....
        • Anteosauria
          • Family Syodontidae
            Syodontidae

            Syodontidae are a possibly paraphyletic Family of smallish primitive Carnivore Dinocephalia. They lack the distinctive 'boss' on the lower jaw, that characterises the Anteosauridae, so they can be considered more primitive....
          • Family Brithopodidae
            Brithopodidae

            Brithopodidae are a paraphyletic Family of primitive mostly carnivorous Dinocephalians known from the Middle Permian of Russia. Nowadays the name is used less often, being replaced by Anteosauria ...
          • Family Anteosauridae
            Anteosauridae

            The Anteosauridae or Anteosaurinae are a Family or subfamily of very large carnivore Dinocephalia that are known from the Middle Permian of Russia and South Africa ....
        • Tapinocephalia
          Tapinocephalia

          The Tapinocephalians are one of the major groups of Dinocephalian therapsids. Unlike Anteosaurs and estemmenosuchidae, the tapinocephalia are mainly from Africa and only one species is found in the north - Ulemosaurus from Russia....
          • Family Titanosuchidae
            Titanosuchidae

            The titanosuchids were carnivorous to omnivorous Tapinocephalia dinocephalians. As with other tapinocephalids, they had thick-skulls probably for head-butting....
          • Family Tapinocephalidae
            Tapinocephalidae

            The Tapinocephalidae are an advanced family of Tapinocephalia. They were all herbivores. They were giants of their time, weighing from 500 to 1000 kg and possibly over 1 or 2 tonnes in weight....
      • Neotherapsida
        • Suborder Anomodont
          Anomodont

          The Anomodontia are one of the three major groups of therapsids, an extinct group of animals commonly known as "mammal-like reptiles." They were mostly toothless herbivorous....
          ia           *
          Paraphyly

          In phylogenetics, a group of organisms is said to be paraphyletic if the group contains its most recent common ancestor Common descent but does not contain all the descendants of that ancestor....
          • Superfamily Venyukoviamorpha
            • Family Venyukoviidae
              • Suminia
                Suminia getmanovi

                Suminia getmanovi was a primitive therapsid that lived 260 mya in the late Permian . This Anomodontia was discovered in Kotelnich on the Vyatka River Russia....
          • Infraorder Dicynodont
            Dicynodont

            The Dicynodontia are a taxon of Therapsids or mammal-like reptiles. Dicynodonts were small to large Herbivore animals with two tusks, hence their name, which means 'two dog tooth'....
            a
        • Theriodont
          Theriodont

          Theriodonts , are the third main group of therapsids. They can be defined in traditional, Linnaean taxonomy terms, in which case they are a suborder of mammal-like reptiles that lived from the Middle Permian to the Middle Cretaceous, or in cladistics terms, in which case they include not only the traditional theriodonts but also their descend...
          ia *
          Paraphyly

          In phylogenetics, a group of organisms is said to be paraphyletic if the group contains its most recent common ancestor Common descent but does not contain all the descendants of that ancestor....
          • Suborder Gorgonopsia
            Gorgonopsia

            Gorgonopsia is a suborder of therapsid synapsids. Their name is a reference to the Gorgons of Greek mythology. Like other therapsids, gorgonopsians were at one time called "mammal-like reptiles", though in most current classifcation systems, they are not true reptiles, but instead are much more closely related to true mammals....
            • Family Gorgonopsidae
              Gorgonopsia

              Gorgonopsia is a suborder of therapsid synapsids. Their name is a reference to the Gorgons of Greek mythology. Like other therapsids, gorgonopsians were at one time called "mammal-like reptiles", though in most current classifcation systems, they are not true reptiles, but instead are much more closely related to true mammals....
          • Eutheriodontia
            • Suborder Therocephalia
              Therocephalia

              Therocephalians are an extinct lineage of eutheriodont therapsids that lived throughout the middle and late Permian and into the Triassic. The therocephalians are named after their large skulls, which, along with their teeth, suggest that most were successful carnivores....
            • Suborder Cynodontia *
              Paraphyly

              In phylogenetics, a group of organisms is said to be paraphyletic if the group contains its most recent common ancestor Common descent but does not contain all the descendants of that ancestor....
              • (unranked) Mammaliformes *
                Paraphyly

                In phylogenetics, a group of organisms is said to be paraphyletic if the group contains its most recent common ancestor Common descent but does not contain all the descendants of that ancestor....
  • Class Mammal
    Mammal

    Mammals are a class of vertebrate animals whose name is derived from their distinctive feature, mammary glands, with which they feed their young....
    ia


Phylogeny

Synapsida | Sphenacodontia
Sphenacodontia

Sphenacodontia is the name given to the clade that includes the Sphenacodontidae and all their descendants . They first appear during the Late Pennsylvanian epoch....
 |-Sphenacodontidae
Sphenacodontidae

The Sphenacodontidae are a family of small to large, advanced, carnivore, Late Pennsylvanian to Guadalupian pelycosaurs. Primitive forms were generally small in size , but during the later part of the early Permian these animals grew progressively larger , to become the Apex predator of their environments....
 `-Therapsida |-?Tetraceratops
Tetraceratops

'Tetraceratops insignis' was a lizard-like synapsid. It lived during the Early Permian period. According to a recent, controversial report, T....
 `-+-Biarmosuchia
Biarmosuchia

The Biarmosuchia, also known as the Eotitanosuchia and the Phthinosuchia are an assemblage of primitive Permian Therapsida that represent either a paraphyletic stem group or a very early off-shoot of the main Therapsid tree....
 | |-Eotitanosuchidae
Eotitanosuchus

Eotitanosuchus olsoni was a Therapsid occurring in the town of Ochyor in Perm Krai, Russia, in channel flood deposits along with Biarmosuchus tener, Estemmenosuchus uralensis and Estemmenosuchus mirabilis....
 | `-?Phthinosuchidae
Phthinosuchus

Phthinosuchus was a therapsid that lived in the Late Permian of Russia. Phthinosuchus is the sole member of its family and suborder, although Phthinosaurus may be a relative....
 `-Eutherapsida |-Dinocephalia
Dinocephalia

Dinocephalia are a cladistics of large early Therapsida that flourished during the Guadalupian, but became extinct leaving no descendants.Apart from the Biarmosuchia and the Eotitanosuchus olsoni, the Dinocephalia are the least advanced among the therapsids, although still uniquely specialised in their own way....
 | |-Anteosauria | `-Tapinocephalia
Tapinocephalia

The Tapinocephalians are one of the major groups of Dinocephalian therapsids. Unlike Anteosaurs and estemmenosuchidae, the tapinocephalia are mainly from Africa and only one species is found in the north - Ulemosaurus from Russia....
 `-Neotherapsida |-Anomodontia | |-Dromasauria
Dromasauria

Dromasaurs are a paraphyletic group of anomodontian therapsids. They were small, but they have slight built, slender legs, and a long tail. Their skulls were short, but the eye sockets were large....
 | `-Dicynodontia `-Theriodontia |-Gorgonopsia
Gorgonopsia

Gorgonopsia is a suborder of therapsid synapsids. Their name is a reference to the Gorgons of Greek mythology. Like other therapsids, gorgonopsians were at one time called "mammal-like reptiles", though in most current classifcation systems, they are not true reptiles, but instead are much more closely related to true mammals....
 | |-Lycaenops
Lycaenops

Lycaenops is a genus of carnivore therapsid . It measured about 1 meter long and lived during the late mid-Permian to the early Late Permian in what is now South Africa....
 | `-Inostrancevia
Inostrancevia

Inostrancevia was a genus of gorgonopsid therapsid found in Sokolki, on the Smaller Northern Dvina River near Arkhangelsk in Russia. The animal lived 251 million years ago during the Late Permian....
 `-Eutheriodontia |-Therocephalia
Therocephalia

Therocephalians are an extinct lineage of eutheriodont therapsids that lived throughout the middle and late Permian and into the Triassic. The therocephalians are named after their large skulls, which, along with their teeth, suggest that most were successful carnivores....
 | `-Eutherocephalia
Eutherocephalia

Eutherocephalians are an infraorder of therocephalians. Most of them survived the Permian?Triassic extinction event....
 | `-Bauria
Bauria

Bauria is an extinct genus of the suborder therocephalia. It belonged to the family Bauriidae. Bauria was probably a carnivore or insectivore....
 `-Cynodontia `-Mammalia

See also

  • Vertebrate paleontology
    Vertebrate paleontology

    Vertebrate paleontology seeks to discover the behavior, reproduction and appearance of extinct animals with vertebrae or a notochord, through the study of their fossilized remains....
  • Evolution of mammals
    Evolution of mammals

    __FORCETOC__The evolution of mammals from synapsids was a gradual process which took approximately 70 million years, beginning in the mid-Permian....
  • Timeline of evolution
    Timeline of evolution

    This timeline of the evolution of life outlines the major events in the development of life on the planet Earth . For a thorough explanatory context, see the history of Earth, and geologic time scale....


External links

  • "" Tree of Life
  • "" Palaeos
  • "". Stephen Priestley - Illustrator