Theriodont
Encyclopedia
Theriodonts are a major group of therapsids. They can be defined in traditional, Linnaean
terms, in which case they are a suborder of mammal-like reptiles that lived from the Middle Permian
to the Middle Cretaceous
, or in Cladistic
terms, in which case they include not only the traditional theriodonts but also their descendants the mammals as well (in the same way that, cladistically speaking, the theropod dinosaurs include the birds as a sub-clade).
Theriodonts appeared almost the same time as the anomodonts, about 265 million years ago, in the Middle Permian. Even these early theriodonts were more mammal-like than their Anomodont and Dinocephalia
n contemporaries.
Theriodonts fall into three main groups: Gorgonopsia
, Therocephalia
and Cynodontia. Early theriodonts may have been warm-blooded
. Early forms were carnivorous, but several later groups became herbivorous during the Triassic
.
Theriodont jaw
s were more mammal-like than was the case of other therapsids, because their dentary was larger, which gave them more efficient chewing ability. Furthermore, several other bones that were on the lower jaw (found in reptile
s), moved into the ear
s, allowing the theriodonts to hear better and their mouths to open wider. This made the theriodonts the most successful group of synapsid
s.
Eutheriodonts refer to all theriodonts except the gorgonopsians (the most primitive group). They included the therocephalians, cynodonts and their descendants - the mammals . The name means "true beast tooth". The eutheriodonts have larger skulls, accommodating larger brain
s and improved jaw muscles.
The theriodonts (eutheriodonts) are one of the two synapsid
survivors of the great Permian–Triassic extinction event, the other being the dicynodont
s. Therocephalians included both carnivorous and herbivorous forms; both died out after the Early Triassic
. The remaining theriodonts, the cynodonts, also included carrnivores such as Cynognathus
, as well as newly evolved herbivorous (Traversodonts
). While Traversodonts for the most part remained medium-sized to reasonably large (length of largest species up to 2 meters), the carnivorous forms became progressively smaller as the Triassic progressed. By the Late Triassic the small cynodonts included the rodent-like tritylodonts (possibly related to or descended from travsersodonts), and the tiny, shrew-like, trithelodonts, which evolved into the first mammals
. The trithelodonts died out during the Jurassic
, and the tritylodonts survived in the Cretaceous
, but the mammals continued to evolve. Many mammal groups managed to survive the Cretaceous–Tertiary extinction event, which wiped out the non-avian
dinosaur
s, allowing the mammal
s to diversify
and dominate the Earth.
Mammals and extinct relatives
* †Biarmosuchia
* †Eotitanosuchia
* †Dinocephalia
* †Anomodontia
* Theriodontia
o †Gorgonopsia
o †Therocephalia
o Cynodontia
+ †Diviniidae
+ Mammalia
+ †Procynosuchidae
+ †Galesauridae
+ †Thrinaxodontidae
+ †Cynognathidae
+ †Gomphodonts
+ †Chiniquodontidae
+ †Probainognathidae
+ †Tritheledontidae (Ictidosauria)
Linnaean taxonomy
Linnaean taxonomy can mean either of two related concepts:# the particular form of biological classification set up by Carl Linnaeus, as set forth in his Systema Naturæ and subsequent works...
terms, in which case they are a suborder of mammal-like reptiles that lived from the Middle Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. 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...
to the Middle Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
, or in Cladistic
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
terms, in which case they include not only the traditional theriodonts but also their descendants the mammals as well (in the same way that, cladistically speaking, the theropod dinosaurs include the birds as a sub-clade).
Theriodonts appeared almost the same time as the anomodonts, about 265 million years ago, in the Middle Permian. Even these early theriodonts were more mammal-like than their Anomodont and Dinocephalia
Dinocephalia
Dinocephalia are a clade of large early therapsids that flourished during the Middle Permian, but became extinct leaving no descendants.-Description:...
n contemporaries.
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"...
, Therocephalia
Therocephalia
Therocephalians are an extinct suborder of carnivorous eutheriodont therapsids that lived from the middle and late Permian into the Triassic 265.0—245.0 Ma existing for approximately ....
and Cynodontia. Early theriodonts may have been warm-blooded
Warm-blooded
The term warm-blooded is a colloquial term to describe animal species which have a relatively higher blood temperature, and maintain thermal homeostasis primarily through internal metabolic processes...
. Early forms were carnivorous, but several later groups became herbivorous during the Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
.
Theriodont jaw
Jaw
The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of...
s were more mammal-like than was the case of other therapsids, because their dentary was larger, which gave them more efficient chewing ability. Furthermore, several other bones that were on the lower jaw (found in reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s), moved into the ear
Ear
The ear is the organ that detects sound. It not only receives sound, but also aids in balance and body position. The ear is part of the auditory system....
s, allowing the theriodonts to hear better and their mouths to open wider. This made the theriodonts the most successful group of synapsid
Synapsid
Synapsids are a group of animals that includes mammals and everything more closely related to mammals than to other living amniotes. They are easily separated from other amniotes by having an opening low in the skull roof behind each eye, leaving a bony arch beneath each, accounting for their name...
s.
Eutheriodonts refer to all theriodonts except the gorgonopsians (the most primitive group). They included the therocephalians, cynodonts and their descendants - the mammals . The name means "true beast tooth". The eutheriodonts have larger skulls, accommodating larger brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
s and improved jaw muscles.
The theriodonts (eutheriodonts) are one of the two synapsid
Synapsid
Synapsids are a group of animals that includes mammals and everything more closely related to mammals than to other living amniotes. They are easily separated from other amniotes by having an opening low in the skull roof behind each eye, leaving a bony arch beneath each, accounting for their name...
survivors of the great Permian–Triassic extinction event, the other being the dicynodont
Dicynodont
Dicynodontia is a taxon of anomodont therapsids or mammal-like reptiles. Dicynodonts were small to large herbivorous animals with two tusks, hence their name, which means 'two dog tooth'...
s. Therocephalians included both carnivorous and herbivorous forms; both died out after the Early Triassic
Early Triassic
The Early Triassic is the first of three epochs of the Triassic period of the geologic timescale. It spans the time between 251 ± 0.4 Ma and 245 ± 1.5 Ma . Rocks from this epoch are collectively known as the Lower Triassic, which is a unit in chronostratigraphy...
. The remaining theriodonts, the cynodonts, also included carrnivores such as Cynognathus
Cynognathus
Cynognathus crateronotus was a meter-long predator of the Early to Middle Triassic. It was among the more mammal-like of the Synapsids, a member of a grouping called Eucynodontia. The genus Cynognathus had an almost worldwide distribution...
, as well as newly evolved herbivorous (Traversodonts
Traversodontidae
Traversodontidae is a family of herbivorous cynodonts. Traversodonts were primarily Gondwanan, with many species known from Africa and South America. Recently, traversodonts have also been found from Europe and eastern North America. Traversodonts first appeared in the Middle Triassic, diversified...
). While Traversodonts for the most part remained medium-sized to reasonably large (length of largest species up to 2 meters), the carnivorous forms became progressively smaller as the Triassic progressed. By the Late Triassic the small cynodonts included the rodent-like tritylodonts (possibly related to or descended from travsersodonts), and the tiny, shrew-like, trithelodonts, which evolved into the first mammals
Mammaliaformes
Mammaliaformes is a clade that contains the mammals and their closest extinct relatives. Phylogenetically, it is defined as a clade including the most recent common ancestor of Sinoconodon, morganuconodonts, docodonts, Monotremata, Marsupialia, Placentalia, extinct members of this clade, and all...
. The trithelodonts died out during the Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
, and the tritylodonts survived in the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
, but the mammals continued to evolve. Many mammal groups managed to survive the Cretaceous–Tertiary extinction event, which wiped out the non-avian
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s, allowing the mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s to diversify
Adaptive radiation
In evolutionary biology, adaptive radiation is the evolution of ecological and phenotypic diversity within a rapidly multiplying lineage. Starting with a recent single ancestor, this process results in the speciation and phenotypic adaptation of an array of species exhibiting different...
and dominate the Earth.
Classification
- Order TherapsidaTherapsidaTherapsida is a group of the most advanced synapsids, and include the ancestors of mammals. Many of the traits today seen as unique to mammals had their origin within early therapsids, including hair, lactation, and an erect posture. The earliest fossil attributed to Therapsida is believed to be...
- Theriodont *ParaphylyA group of taxa is said to be paraphyletic if the group consists of all the descendants of a hypothetical closest common ancestor minus one or more monophyletic groups of descendants...
- Suborder †GorgonopsiaGorgonopsiaGorgonopsia 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"...
- Family †Gorgonopsidae
- Eutheriodontia
- Suborder †TherocephaliaTherocephaliaTherocephalians are an extinct suborder of carnivorous eutheriodont therapsids that lived from the middle and late Permian into the Triassic 265.0—245.0 Ma existing for approximately ....
- Family †Lycosuchidae
- (unranked) †ScylacosauriaScylacosauriaScylacosauria is a clade of therocephalian therapsids. It includes the basal family Scylacosauridae and the infraorder Eutherocephalia. Scylacosauridae and Eutherocephalia form this clade to the exclusion of Lycosuchidae, the most basal therocephalian family. Thus, Scylacosauria includes all...
- Family †ScylacosauridaeScylacosaurusScylacosaurus is an extinct genus of therapsid....
- Family †Scylacosauridae
- Infraorder †EutherocephaliaEutherocephaliaEutherocephalia is an infraorder of therocephalian therapsids. Eutherocephalians are distinguished from the lycosuchids and scylacosaurids, two early therocephalian families. While lycosuchids and scyalosaurids went extinct by the end of the Permian period, eutherocephalians survived the...
- Family †HofmeyriidaeHofmeyriaHofmeyria is an extinct genus of non-mammalian synapsid.-References:*...
- Family †MoschorhinidaeMoschorhinidaeAkidnognathidae is a family of small therocephalian therapsids.-Ecology:Akidnognathids were carnivores, hunting prey such as Dicynodonts....
- Family †WhaitsiidaeWhaitsiaWhaitsia is an extinct genus of therocephalian therapsid.-References:*...
- Superfamily †BaurioideaBaurioideaBaurioidea is a superfamily of therocephalian therapsids. It includes advanced therocephalians such as Regisaurus and Bauria. The superfamily was named by South African paleontologist Robert Broom in 1911. Bauriamorpha, named by D. M. S. Watson and Alfred Romer in 1956, is a junior synonym of...
- Family †BauriidaeBauriaBauria is an extinct genus of the suborder therocephalia. It belonged to the family Bauriidae. Bauria was probably a carnivore or insectivore.thumb|200px|left|Bauria...
- Family †EriciolacteridaeEriciolacertaEriciolacerta was a small therocephalian therapsid from the early Triassic of South Africa and Antarctica. It was around in length, with long limbs and relatively small teeth. It was probably fairly active, and ate insects and other small invertebrates....
- Family †Ictidosuchidae
- Genus †IctidosuchoidesIctidosuchoidesIctidosuchoides is an extinct genus of ictidosuchid therocephalian. Fossils have been found from the Karoo Basin in South Africa. The genus is known to have been one of the few therocephalians to have survived the Permian-Triassic extinction event in this area, although its numbers were quite low...
- Genus †IctidosuchusIctidosuchusIctidosuchus is a genus of therocephalian therapsid.-References:*...
- Genus †Ictidosuchoides
- Family †IctidosuchopsIctidosuchopsIctidosuchops is a genus of therocephalian therapsid.-References:*...
idae - Family †Lycideopsidae
- Family †Bauriidae
- Family †Hofmeyriidae
- Suborder †Therocephalia
- Suborder †Gorgonopsia
- Theriodont *
Phylogenetics of Theriodontia from Tree of Life (www.tolweb.org)
TherapsidaMammals and extinct relatives
* †Biarmosuchia
* †Eotitanosuchia
* †Dinocephalia
* †Anomodontia
* Theriodontia
o †Gorgonopsia
o †Therocephalia
o Cynodontia
+ †Diviniidae
+ Mammalia
+ †Procynosuchidae
+ †Galesauridae
+ †Thrinaxodontidae
+ †Cynognathidae
+ †Gomphodonts
+ †Chiniquodontidae
+ †Probainognathidae
+ †Tritheledontidae (Ictidosauria)
External links
- Theriodontia - at Paleos