A NEW TRIASSIC VERTEBRATE FAUNA FROM SOUTH WEST AFRICA

A new fauna of mammal-like reptiles is described from a continental sequence of sediments in South West Africa hitherto known as the Etjo Beds. These include representatives of the Anomodontia (two new forms and one known from the Karroo basin), Bauriamorpha, (one specimen comparable with a known form), Cynodontia (one new form and two known from the Karroo basin) and one small eriopoid amphibian. On the basis of this faunal assemblage it can be shown that there is a disconformity between the upper Plateau Sandstone Formation containing traces of Dinosaurs of possible Carnian-Norian age and a lower Omingonde Mudstone Formation with this new fauna, of essentially Upper Beaufort (Scythian/Anisian) age. The two formations are distinguished on lithological grounds. The Triassic sequence in the neighbouring Doros area is thought to be equivalent to the Plateau Sandstone Formation

EVOLUTIONARY TRENDS IN TRIASSIC DICYNODONTIA

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

A RE-EVALUATION OF THE GENUS TROPIDOSTOMA SEELEY

The type specimens of Cteniosaurus platyceps Broom, Dicynodon acutirostris Broom, and Dicynodon validus Broom were re-examined and were found to be very similar in a number of features rarely encountered in other Anomodontia. The skull of the type of Cteniosaurus platyceps is described in some detail. It is concluded that the above species must be considered to be junior synonyms of Tropidostoma microtrema (Seeley)

Effects of diabatic heating on the ageostrophic circulation of an upper tropospheric jet streak

Interaction between the mass circulation within a mesoscale convective complex (MCC) and a direct mass circulation in the entrance region of an upper tropospheric polar jet streak was examined within the isentropic structure to investigate mechanisms responsible for linking these two scales of motion. The results establish that latent heating in the MCC modifies the direct mass circulation in the jet streak entrance region through the diabatically induced components of ageostrophic motion analyzed within isentropic coordinates. Within the strong mesoscale mass circulation of each MCC, strong horizontal mass flux convergence into the MCC at low levels is balanced by strong horizontal mass flux divergence away from the convergence at upper levels. Locations of large diabatic heating rates correspond well to the MCC position for each case; diabatic heating forces the upward vertical branch for the mesoscale mass circulation