Triassic Dicynodontia differ from most of their Permian ancestors in a number of
specialisations that reach extremes in the Upper Triassic. These are ( 1) increase in total body size,
(2) increase in the relative length of the snout and secondary palate by backward growth of the
premaxilla, (3) reduction in the length of the fenestra medio-palatinalis combined with
posterior migration out of the choanal depression, (4) shortening and dorsal expansion of the
intertemporal region, (5 ) fusion of elements in the front part of the brain-case, (6) posterior
migration of the reflected lamina of the mandible, (7) disappearance of the quadrate foramen
and the development of a process of the quadrate that extends along the quadrate ramus of the
pterygoid. It is thought that the occurrence of the last feature in Dinodontosaurus platygnathw Cox
and Jacheleria colorata Bonaparte warrants the transfer of the species platygnathus to the genus
Jacheleria and the erection of a new subfamily, Jachelerinae nov.
It is concluded that the specialisations of the Triassic forms can be attributed to adaptation to
a Dicroidium-dominated flora
