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Author's note: these pages were written some years ago. I am not planning to update them. For a more current coverage, see the link to palaeos com Palaeos website (to which many links on these pages point to anyway. More info here


Anomodontia

beaked herbivores


Cistecephalus - late Permian period

grafic from Illustrated Encyclopaedia of Dinosaurs and Prehistoric Animals, ed. Barry Cox, et al. illustration by Steve Kirk)

Note: in the Linnean ranking the Anomodontia is traditionally considered a suborder of the order Therapsida.  But I feel this diverse and unique group certainly deserves ordinal status, representing as it does a major evolutionary radiation of Permo-Triassic Theropsids.

The Anomodonts

One of the three major evolutionary lines (clades) deriving from the early therapsida (the biarmasuchia/phthinosuchian/Eotitanosuchia base), were the anomodonts, or mostly toothless herbivores. These developed at first (during the link to palaeos com Wordian and link to palaeos com Capitanian epoches) along several paths of adaptive radiation, such as the venyukoviarnorphs, the Dromasauria, and the Eodicynodont, Endothiodont. and the higher Dicynodonts. Of those groups only the higher Dicynodontia were to be successful, and in fact these stocky, toothless and beaked animals remained the dominant terrestrial herbivores right up until the Carnian epoch (late Triasisc period).

Suborder Venjukoviamorpha (incl. Dromasauria)

The venyukoviamorphi, represented by a handful of genera, seem to be intermediate in position between the ancestral therapsid condition and the dicynodonts. In these reptiles, as exemplified by the genus Venyukovia from the Capitanian (middle Permian) of Russia, there was a reduction in the dentition, and the skull exhibited changes in proportions that were clearly related to the highiy evolved skull in the dicynodonts

Very different at first glance are the Dromasaurs. These are small therapsids, with a slight build, slender legs and long tail. The skull is short, with very large orbits (eye sockets). It has been suggested that these animals were actually juveniles, but no adult forms have been found, and it is more likely that they simply resepresent part of the early anomodont radiation.

note by Christian Kammerer: Dromasaurs are undoubtedly an artificial group, and they are actually quite anomodontian if you consider venyukoviamorphs typical basal anomodonts. Actually, the most basal "dromasaurs" may form a clade (Galechiridae) consisting of Galechirus, Galepus, and Patranomodon, but Galeops is probably even closer to the dicynodonts than several "venyukoviamorphs".  Several wonderful new basal anomdonts (for example Suminia, Anomocephalus) have been described recently and greatly elucidate basal anomodont relationships.

family Dromasauridae
family Galechiridae
family Venjukoviidae
family Galeopsidae
       

Suborder Dicynodontia

Diictodon
Diictodon

image from Gillian M. King, The Dicynodonts - A study in palaeobiology

The dicynodonts were the most successful of the therapsids in terms of phylogenetic longevity, numbers of individuals, and the extent of distribution over continental areas. In fact they were the most successful and wide-ranging group of plant-eating animals of the time. They first appeared in mid Permian times (Wordian epoch) with the small Eodicynodon, and evolved in a remarkably uniform structural pattern, as seen in Dicynodon, through the late Permian and the whole of Triassic period. During link to palaeos com late Permian times they were among the commonest of all reptiles, at least as indicated by the fossil record, and a large number of different lineages existed side by side, from small mole like burrowers to giant ox-sized browsers.

They were greatly decimated by the increasingly harsh conditions of the terminal Permian, and only two lineages, the medium-sized Lystrosaurs (especially adapted not to swamps (a spreviously thought) but arid conditions) and the tiny Myosaurs, survived into the link to palaeos com early Triassic. The Myosaurs eventually died out (probably through competition with other herbivores) but the Lystrosaurs evolved into the giant and very succesful Kanneymeriids, pig to rhino sized animals that continued to the end of Carnian epoch (late Triassic period).

The Dicynodonts as a whole lasted some 50 million years, and the only group of therapsids to outlive them were the cynodonts, which were the direct ancestors of the mammals.

It is in the skull that the dicynodonts show their greatest specialiations; there was no other quite like it, certainly not among the therapsids (although the large herbivorous rhynchosaurs also developed a similiar beak). The advanced development of their skulls and jaws was the main factor in the success of these animals. The temporal openings at the back of the skull that are shared by all synapsid reptiles were greatly enlarged, so that the remaining bone formed long arches. These large openings supported very powerful jaw muscles. The dicynodonts skull is striking because of its light open constmction and the presence of long, bony bars rather than broad platelike areas behind the eye.

The hinge (see Emydops jaw movement, above) between the lower jaw and the skull permitted the jaws to move forward and backward, with a strong, shearing action, And the dentition of these reptiles was unique. The front of the skull and the lower jaw were narrow and beak-like. Apart from a pair of large, upper tusks in some species, teeth were reduced to tiny remnants or were completely absent. In many dicynodonts the tusks are present in about half of the individuals, indicating that these were probably sexual characters, presumably present in the males and absent in the females.

The upper and the lower jaws were certainly covered with horny beaks in life, like the beak in turtles and, it can be assumed, in the Triassic rhynchosaurs.

The body was short and broad, and was supported by strong limbs thick limbs that supported the body in the typical therapsid fashion. The ilium as expanded and strong, and likewise he shoulder girdle was large and strong. It seems that the hind-limb was held straighter than the forelimb (at least in the case of the Triassic Dinodontosaurus), making them slow plodders but nevertheless with a very powerful thrusting movement. The tail was short, even more so than in other types of therapsids.

In size the dicynodonts ranged from small rodent-like animals about 20cm in length, such as Cistecephalus and other small link to palaeos com Permian forms, to giant, massive animals, such as the link to palaeos com late Triassic genera Stahleckeria (known from Brazil) or Placerias (from Arizona), which were as big as the largest dinocephalians (reaching weights of over a tonne).

Infraorder Eodicynodontia

family Eodicynodontidae


Infraorder Endothiodontia

family Endothiodontidae


Infraorder Pristerodontidia

Superfamily Dicynodontoidea
family Cryptodontidae
family Aulacephalodontidae
family Dicynodontidae

Superfamily Dicynodontoidea (continued...)

Superfamily Pristerodontoidea

family Lystrosauridae
family Kannemeyeriidae
family Pristerodontidae
 
 

Infraorder Diictodontia

Superfamily Emydopoidea
Superfamily Robertoidea
family Emydopidae
family Cistecephalidae
family Robertiidae
family Diictodontidae
 
 

Infraorder Kingoriamorpha

family Kingoriidae



some printed references some Links and References Web links

cladogramAnomodontia after Cox and Anomodontia after Chinsamy, A. & Rubidge - cladograms by Mikko K. Haaramo

printed referenceCarroll, R. L. Vertebrate paleontology and evolution. -W. H. Freeman and company, New York, 1988

printed referenceEdwin H. Colbert, Evolution of the Vertebrates, 2nd edition, 1969, John Wiley & Sons, pp. 135-137

printed referenceJames A. Hopson, "The Origin and Adaptive Radiation of Mammal-Like Reptiles and Non-Therian Mammals, Annals of the New York Academy of Sciences 167:199-216, 1969

printed referenceJames A. Hopson and Herbert R. Barghusen, "An Analysis of Therapsid Relationships", in The Ecology and Biology of Mammal-Like Reptiles ed. by Nocholas Hotton III, Paul D. MacLean, Jan J. Roth and E. Carol Roth, Smithsonian Institute Press, Washington and London, 1986, pp.83-106

printed referenceGillian M. King, "Anomodontia" Part 17 C, Encyclopedia of Paleoherpetology, Gutsav Fischer Verlag, Stuttgart and New York, 1988

printed referenceGillian M. King, The Dicynodonts - A study in palaeobiology, Chapman and Hall, London and New York, 1990

printed referenceModesto, S., B. Rubidge, and J. Welman. 1999. "The most basal anomodont therapsid and the primacy of Gondwana in the evolution of the anomodonts." Proceedings of the Royal Society of London, B. 266:331-337

printed referenceRubidge, B. and J.A. Hopson. 1990. "A new anomodont therapsid from South Africa and its bearing on the ancestry of Dicynodontia". South African Journal of Science. 86:43-45


Therapsida main page

link to palaeos com Permian Period link to palaeos com Triassic Period Therapsida



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page by M.Alan Kazlev
page uploaded 8 August 1998. Reposted and last modified 1 September 2005, links updated 16 January 2010