'' life-sized model The dicynodont
skull is highly specialised, light but strong, with the
synapsid temporal openings at the rear of the skull greatly enlarged to accommodate larger jaw muscles. The front of the skull and the lower jaw are generally narrow and, in all but a number of primitive forms, toothless. Instead, the front of the mouth was equipped with a
keratinous horny
beak, as in
turtles and
ceratopsian
dinosaurs. Food was processed by the retraction of the lower jaw when the mouth closed, producing a powerful shearing action, which would have enabled dicynodonts to cope with tough plant material. Dicynodonts typically had a pair of enlarged maxillary caniniform teeth, analogous to the
tusks present in some living mammals. In the earliest genera, they were merely enlarged teeth, but in later forms they independently evolved into ever-growing teeth like mammal tusks multiple times. In some dicynodonts, the presence of tusks has been suggested to be
sexually dimorphic. Some dicynodonts such as
Stahleckeria lacked true tusks and instead bore tusk-like extensions on the side of the beak. Like some other anomodonts, the skull roof shows the development of a novel skull bone, the "preparietal" that is not found in earlier synapsids nor in the cynodont ancestors of mammals. It is unpaired and forms the anterior (forward) margin of the
pineal foramen. Similar bones, also called "preparietals" are found in
gorgonopsid and
biarmosuchian therapsids, though these are thought to have
evolved convergently in each group. Dicynodonts ancestrally had three vertebrae in the
sacrum, though this rose to over 6 vertebrae in some dicynodonts as a result of both vertebrae duplication and incorporation of
caudal vertebrae into the sacrum. Dicynodonts vary enormously in size. The smallest were rat-sized, a size common amongst Permian members of the group, while Triassic members of the group were typically much larger, with the youngest known member
Lisowicia also being the largest known, around the size of an elephant, with a body mass estimated at . Many at least Triassic dicynodonts may have held their hindlimbs in a relatively erect posture while having more splayed forelimbs, though
Lisowicia likely to have had erect forelimbs as well. However specimens of
Lystrosaurus fossilized with mummified skin have found that the skin surface was covered in numerous overlapping
tubercules.
Pentasauropus dicynodont tracks suggest that dicynodonts had fleshy pads on their feet.
Possible endothermy Dicynodonts have long been suspected of being
warm-blooded animals. Their bones are highly vascularised and possess
Haversian canals, and their bodily proportions are conducive to heat preservation. In young specimens, the bones are so highly vascularised that they exhibit higher channel densities than most other therapsids. Yet, studies on
Late Triassic dicynodont
coprolites paradoxically showcase digestive patterns more typical of animals with slow metabolisms. A 2017 study using chemical analysis suggested that cynodonts and dicynodonts both developed warm blood independently before the Permian extinction.
Reproduction '' from the Early Triassic of South Africa, with life restoration showing embryo curled up in inferred (but unpreserved) egg A preserved tightly curled embryonic individual of
Lystrosaurus from the Early Triassic of South Africa suggests that dicynodonts laid eggs, as is thought to be ancestral for
synapsids and
amniotes, though the lack of preserved eggshell suggests that the eggs were probably soft and leathery like in living
monotreme mammals, and as is suggested to be ancestral for amniotes. The relatively large size of the eggs suggests individuals of
Lystrosaurus were
precocial (relatively independent from birth), and the egg had large
yolk reserves for development, indicating that dicynodonts did not produce milk like mammals (the eggs of milk-producing monotremes are relatively small compared to body size) and perhaps at least some non-mammalian cynodonts. == History of discovery and research ==