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Dicynodont
 
 
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The Dicynodontia are a taxon
Taxon

A taxon or taxonomic unit is a name designating an organism or a group of organisms. In biological nomenclature according to Carl Linnaeus, a taxon is assigned a taxonomic rank and can be placed at a particular level in a systematic hierarchy reflecting evolutionary relationships....
 of Therapsids or mammal-like reptiles. Dicynodonts were small to large herbivorous
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....
 animals with two tusks, hence their name, which means 'two dog tooth'. They are also the most successful and diverse of the non-mammalian therapsids, with over 70 genera
Genus

A genus is a low-level taxonomic rank used in the classification of living and fossil organisms. The taxonomic ranks are domain , kingdom , phylum, class , order , family , genus, and species....
 known, varying from rat- to ox-sized.

Dicynodont skull is highly specialised; light but strong, with the synapsid temporal openings at the rear of the skull are greatly enlarged, to accommodate larger jaw muscles.

The front of 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 lower jaw are generally narrow and, in all but a number of primitive forms, toothless.






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The Dicynodontia are a taxon
Taxon

A taxon or taxonomic unit is a name designating an organism or a group of organisms. In biological nomenclature according to Carl Linnaeus, a taxon is assigned a taxonomic rank and can be placed at a particular level in a systematic hierarchy reflecting evolutionary relationships....
 of Therapsids or mammal-like reptiles. Dicynodonts were small to large herbivorous
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....
 animals with two tusks, hence their name, which means 'two dog tooth'. They are also the most successful and diverse of the non-mammalian therapsids, with over 70 genera
Genus

A genus is a low-level taxonomic rank used in the classification of living and fossil organisms. The taxonomic ranks are domain , kingdom , phylum, class , order , family , genus, and species....
 known, varying from rat- to ox-sized.

Characteristics

The Dicynodont skull is highly specialised; light but strong, with the synapsid temporal openings at the rear of the skull are greatly enlarged, to accommodate larger jaw muscles.

The front of 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 lower jaw are generally narrow and, in all but a number of primitive forms, toothless. Instead, the front of the mouth is equipped with a horny beak, as in turtles and ceratopsia
Ceratopsia

Ceratopsia or Ceratopia is a group of herbivore, beaked dinosaurs which thrived in what are now North America and Asia, during the Cretaceous Period , although ancestral forms lived earlier, in the Jurassic....
n dinosaur
Dinosaur

Dinosaurs were the dominant vertebrate animals of Landform ecosystems for over 160 million years, from the late Triassic Period until the end of the Cretaceous Period , when most of them became extinct in the Cretaceous?Tertiary extinction event....
s. Food was processed through retraction of the lower jaw when the mouth closed, producing a powerful shearing action (Crompton and Hotton 1967), which would have enabled dicynodonts to cope with tough plant material.

Many genera also have a pair of tusks, which it is thought may have been an example of sexual dimorphism
Sexual dimorphism

Sexual dimorphism is the systematic difference in form between individuals of different sex in the same species. Examples include color , size, and the presence or absence of parts of the body used in courtship displays or fights, such as ornamental feathers, horns, antlers or tusks....
 (Colbert 1969 p.137)

The body is short, strong and barrel-shaped, with strong limbs. In large genera (such as Dinodontosaurus
Dinodontosaurus

Dinodontosaurus is a genus of dicynodont therapsid. It was one of the largest herbivores of the Triassic and had a beak corneum. It lived in the Middle Triassic but disappeared in the Upper Triassic....
) the hindlimbs were held erect, but the forelimbs bent at the elbow. Both the pectoral girdle
Pectoral girdle

The pectoral girdle is the set of bones which connect the upper limb to the axial skeleton on each side. It consists of the clavicle and scapula in humans and, in those species with three bones in the pectoral girdle, the coracoid....
 and the ilium
Ilium (bone)

The ilium is the uppermost and largest bone of the pelvis, and appears in most vertebrates including mammals and birds, but not bony fish. All reptiles have an ilium except snakes, although some snake species have a tiny bone which is considered to be an ilium....
 are large and strong. The tail is short.

Evolutionary history

Dicynodonts first appear during Middle Permian, and underwent a rapid evolutionary radiation
Evolutionary radiation

An evolutionary radiation is an increase in taxonomy diversity or Morphology disparity, due to adaptation change or the opening of ecospace. Radiations may affect one clade or many, and be rapid or gradual; where they are rapid, and driven by a single lineage's adaptation to their environment, they are termed adaptive radiations....
, becoming the most successful and abundant land vertebrates of the Late Permian. During this time they including a large variety of ecotypes, including large, medium-sized, and small herbivores and short-limbed mole-like burrowers.

Only two families survived the end Permian extinction, one of which, the Lystrosauridae
Lystrosaurus

Lystrosaurus was a genus of Late Permian and Early Triassic Period dicynodont therapsids, which lived around 250 million years ago in what is now Antarctica, India and South Africa....
, were the most common and widespread herbivores of the Induan
Induan

The Induan is the first faunal stage of the Early Triassic epoch . It spans the time between 251 ? 0.4 annum and 249.7 ? 0.7 Ma . This stage follows the Permian-Triassic extinction event of the late Permian period....
 (earliest 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....
). These medium-sized animals evolved into and were replaced by the Kannemeyeridae, stocky, pig- to ox-sized animals that were the most abundant herbivores worldwide from the Olenekian
Olenekian

The Olenekian is a faunal stage of the Early Triassic epoch . It spans the time between 249.7 ? 0.7 annum and 245 ? 0.7 Ma . The Olenekian is divided into the Smithian and the Spathian age....
 to the Ladinian
Ladinian

The Ladinian is a faunal stage of the Middle Triassic epoch . It spans the time between 237 ? 2 annum and 228 ? 2 Ma . The Ladinian was preceded by the Anisian Stage and succeeded by the Carnian Stage of the Late Triassic Period....
 age. By 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....
 they had been supplanted by Traversodont
Traversodontidae

Traversodonts were a group of herbivore cynodonts. Their postcanine teeth is modified and expanded in width for chewing plants. Traversodonts had relatively wide snouts, and the maxilla extends sidewards beyond the teeth....
 cynodonts and rhynchosaur
Rhynchosaur

Rhynchosaurs were a group of unusual Triassic diapsid reptiles related to the Archosauria. They were herbivores, and at times abundant , with stocky bodies and a powerful beak....
 reptiles. During the Norian
Norian

The Norian Stage was a portion of the Triassic geological period. It dates from 216.5 ? 2.0 to 203.6 ? 1.5 Mya . It was preceded by the Carnian Stage and succeeded by the Rhaetian Stage....
 (middle of the Late Triassic), when - perhaps due to increasing aridity - they drastically declined, and the role of large herbivore was taken over by sauropodomorph dinosaurs.

With the decline and extinction of the Kannemeyerids, there were to be no more dominant large synapsid herbivores until the middle Paleocene
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 ....
 epoch (60 Ma) when 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, descendants of 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, began to diversify after the extinction of the dinosaurs.

It used to be thought that Dicynodonts died out completely before the end of the Triassic. Recently however, evidence has come to light showing the dicynodonts survived into the 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....
 in southern 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. (now Queensland
Queensland

Queensland is a States and territories of Australia of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory to the west, South Australia to the south-west and New South Wales to the south....
) (Thulborn and Turner, 2003).

Systematics


Taxonomy

  • Infraorder Dicynodontia
    • Genus Colobodectes
    • Superfamily Eodicynodontoidea
      • Family Eodicynodontidae
    • Superfamily Kingorioidea
      • Family Kingoriidae
    • Clade Diictodontia
      • Superfamily Emydopoidea
        • Family Cistecephalidae
        • Family Emydopidae
      • Superfamily Robertoidea
        • Family Diictodontidae
        • Family Robertiidae
    • Clade Pristerodontia
      • Genus Dinanomodon
      • Genus Odontocyclops
      • Genus Propelanomodon
      • Family Aulacocephalodontidae
      • Family Dicynodontidae
      • Family Kannemeyeriidae
        Kannemeyeriidae

        Kannemeyeriidae is a family of large, stocky, beaked and sometimes tusked dicynodonts, they were the dominant large terrestrial herbivorous through most of the Triassic....
      • Family Lystrosauridae
      • Family Oudenodontidae
      • Family Pristerodontidae
      • Family Shanisiodontidae
      • Family Stahleckeriidae


Phylogeny

The cladogram presented here follows a synthesis from .

See also

  • Dicynodon
    Dicynodon

    Dicynodon is a type of herbivore mammal-like reptile that flourished during the Permian Period . This animal was toothless, except for prominent tusks, hence the name....
  • 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....
  • 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....


External links

  • - Palaeos