The Permian dinocephalians - the name means "terrible head" and is a reference to their fierce appearance, were in many ways the most archaic of the higher therapsids, among the earliest as well. Although these reptiles showed therapsid adaptations such as the expansion of the ilium and the general pose of the limbs, they retained various primitive characters of the pelyosaurs. For example they had no secondary palate, and their dentary bone was of moderate size (in the more mammal-like and advanced group, the Cynodonts the dentary bone of the lower jaw grew increasingly large, until it constituted the entire jaw, which is the mammalian condition). The Dinocephalians are also distinguished by their large size (the biggest were the size of an adult rhinoceros), and the pachyostosis, or thickening of the bones in the skull, an adaptation for intra-specific rivalry (head-butting) to procure territory or a mate.
A number of writers have included the dinocephalians in the suborder Anomodontia, but it is now acknowledtged they constitute a seperate group. The dinocephalians are divided into two main groups, the mostly carnivorous Anteosaurs (which included giants upto 6 meters and more in length), and the medium to very large herbivorous Estemmnosuchids and Tapinocephalia (the latter again divided into two branches, the titanosuchians, which were large ponderous herbivores or omnivores, and the tapinocephalians, which were equally large and ponderous but more specialised as purely herbivores), which reached the size of an ox or even a rhinoceros in the larger species. The brithopodids clearly preyed largely on their estemmenosuchid and tapinocephalian cousins.
The Dinocephalians are an ancient group and their ancestry is not clear. It is assumed that they must have evolved during the earlier part of the Ufimian/Roadian, or even Kungurian epoch, but no trace has been found; the fauna described by Olson of this age has turned out on reinspection to be not therapsid but misinterpretation of caseid remains [ref. pers. communication Christian Kammerer]. Even the earliest members, the estemmenosuchids and early brithopodids of the Russian Ocher fauna, (late Roadian or early Wordian age) were a diverse group of herbivores and carnivores.
All Dinocephalians are distinguished by the interlocking incisor (front) teeth. Correlated features are the distinctly downturned facial region, deep temporal region, and forwardly rotated suspensorium. The way the jaw mechanism works is shown here.
Shearing contact between upper and lower teeth (allowing food to be more easily sliced into small bits for digestion) is achieved through keeping a fixed quadrate and a hinge-like movement at the jaw articulation. The lower teeth are inclined forward, and occlusion is achieved by the interlocking of the incisor teeth.
The later dinocephalians improved on this system by developing heels on the lingual sides of the incisor teeth which met against one another to form a crushing surface when the jaws were shut.
The dinocephalians were originally carnivorous, as represented by the Brithopodids, but even the earliest Estemmenosuchids, and then the somewhat later titanosuchids and tapinocephalids adapted to a herbivorous life-style, replaciong the big Caseid pelycosaurs as the dominant plant eaters. In all dinocephalians the synapsid opening for attachment of jaw muscles remained relatively small, and it is assumed that the power of the bite was provided by the sheer mass of the animals jaw and muscles. This was a less efficient sysrtem than in the anomodonts and theriodonts, but it clearly worked well, because these creatures dominated the large herbivore and large carnivore niche for some millions of years
At the end of mid-Permian time (mid or late Capitanian age) all the dinocephalians become extinct. The reason for this is not clear, and I find the conventional explanation that they were outcompeted by the more efficient herbivorous anomodonts and carnivorous theriodonts about as persuasive as the old idea that the mammals outcompeted the dinosaurs. Possibly disease, sudden climatic change, or other factors of environmental stress brought about their end. With their passing some of the most interesting prehistoric creatures this Earth has seen disappeared; they were replaced by much smaller dicynodonts and theriodonts.
The following five families are recognised
|some Links and References|
Dinocephalia after Carroll 1988 - cladogram and genus list, based on Carroll (see next reference) - Mikko K. Haaramo
L. D. Boonstra, "The Fauna of the Tapinocephalus Zone (Beaufort Beds of the Karoo)", Annals of the South African Museum, 56 (1) 1969, pp. 1-73
Carroll, R. L. Vertebrate paleontology and evolution. -W. H. Freeman and company, New York, 1988
Edwin H. Colbert, Evolution of the Vertebrates, 2nd edition, 1969, John Wiley & Sons, pp. 135-137
James 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
James 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
Gillian M. King, "Anomodontia" Part 17 C, Encyclopedia of Paleoherpetology, Gutsav Fischer Verlag, Stuttgart and New York, 1988
Everett C. Olson, "Late Permian Terrestrial Vertebrates, USA and USSR", Transactions of the American Philosophical Society, Philadelphia, vol 52 part 2, 1962