Major Subgroups



There are a variety of successive preservation zones within the fossil record, highlighting the development and evolution of the dicynodont form.



Taphinocephalus Zone



The Taphinocephalus zone provides fossils of the first dicynodont forms. The forms are small but had developed many of the features known in the higher dicynodont. There land was swampy, interrupted by rivers, lakes and forest. The climate was seasonal and therefore herbivores would have to have a mixed diet of fruit, leaves and groundcover or else hibernate (see burrowing) (King, 1990).



Eodicynodon



(Family Eodicynodontidae)

This was an early South African form from the Taphinocephalus zone.  It had not developed the more complex masticatory systems of later forms. It had good back and forth movement of the jaw, however, the secondary palette is small as the premaxilla has not expanded. As a result, Eodicynodon had no extensive contact processes or muscle guidance system (King, 1990).



Diictodon



(Family: Diictodontidae)

Present in South Africa but at a later date found in Zambia and China. Very abundant in numbers within the fossil record. Diictodontidae were higher dicynodonts with the following features:
(King, 1990)

In Diictodon, there is a complete loss of post canine teeth, and less of a reliance on the palatine for mastication. A distinctive notch at the front of the mouth may have functioned in order to chop very resistant plant material (King, 1990). Diictodon produced helical burrow systems (burrowing) and had well developed forelimbs. Furthermore, a laterally flexible vertebral column would have aided excavation and movement within burrow systems (Ray and Chinsamy, 2003). Diictodon also showed a high level of sexual dimophism (tusk ornamentation of males). This is the oldest claim of sexual dimoprhism in the fossil record (Sullivan et al., 2003).



Robertia



(Family: Robertiidae)

Shares many of Diictodon characters such as a notch on maxilla and possesson of canniform process. However, has a moderately wide skull roof and post canine teeth. Palatines are not relied upon and therefore reduced. Lower jaw teeth are present and there is a variable amount of teeth behind the tusk. Robertia retains the sprawling locomotion of the reptilia and has extensive postural musculature. There is a possibility that these forms dug with their forelimbs. They also had long, sharp claws - possibly to aid digging (King, 1990).

robertia
Figure 2.1. Skeleton of Robertia from the Upper Permian (Benton, 1995).



Emydops



(Family Emydopidae)

Emydops has a reducion in teeth on the lower jaw. Teeth are small and irreguar. Widening of this intertemporal regon is a more primitive feature, later forms are narrower with down-turned sides. This broad surface does not have the advantageous sharp sides for muscle attachment.  Later dicynodonts have a narrower region in which powerful jaw muscles can attach (King, 1990).



Cistecephalus Zone



Peak in dicynodont diversity, with approximately 35 genera. The larger dicynodonts have now radiated. There was also a spread in geographic distrubution to the southern Pangean continents (King, 1990).



Oudenodon



(Family: Oudenodontidae)

The family have a deep, thin walled cleft in the lower jaw for anchoring the horny platform. They had a very precise cutting and crushing surface between the beaks, where the rim of the maxilla was pointed downward to fit with the lower jaw symphisis. Oudenodon had no teeth at all. The skull was directed forwards, therefore, adapted to feeding at levels approximately 20-100cm above the ground (King, 1990). This shows a new level of diversification, away from substrate-feeding. 



Dicynodon



(Family: Dicynodontidae)

This is the type specimen of the dicynodonts as it was the first to be found. It can be found in South Africa, Zambia, USSR and China. It is a varied form. The skull has tusks in the upper jaw but the lower jaw is completely toothless. Sharp maxillary ridge for good attachment of powerful muscles. Covered in horny platforms. Very generalised postcranial skeleton. Not very quick as  retained the sprawling position of limbs. There is dispute over whether the genus was aquatic due to the higher position of the nostrils (King, 1990).



Kingoria



(Family: Kingoriidae)

This was a substrate feeder with a large dentary shelf and blunt, shovel-shaped lower jaw beak. Tusks were either present or absent. The head was directed downwards for feeding on substrate. Hindlimbs parallel to body and more modified than forelimbs. Hindlimbs adapted for agility, whereas forelimbs for power (King, 1990).



Cistephalus



(Family: Cistecephalidae)

Reduced palatine and a sharp cutting edge. Occiput is broad and slightly convex as in present day burrowers (see burrowing adaptations) for the attachment of powerful neck and shoulder muscles. This genera is very muscular in general (King, 1990).



Daptocephalus Zone



Spread over South Africa, China, Tanzania, Zambia, the USSR and Scotland. Dicynodonts seen to be among the substrate-feeders. There is a slump in diversty with only 7 genera. Oudenodon and Dicynodon became more common, however, most genera declined to inexistence. The zone has a very poor fossil record (King, 1990).



Lystrosaurus Zone



Covered all the southern continents apart from South America. In the lower part of the Triassic there were 2 genera:
There is a greater proportion of carnivora and increased impovrishment for herbivores due to floral changes occurring as climate was warming as land masses coalesced to form Pangea (King, 1990).



Lystrosaurus



(Family: Lystrosauridae)

Most specialised of the Triassic forms. Possibly aquatic as the pelvic girdle looks to be adapted for water. Perhaps it fed in water (King, 1990).



Characters and anatomy
Major subgroups
Fossil record and evolution
Modern forms
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