Volume 21 1978
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Item Palaeontologia africana Volume 21(Bernard Price Institute for Palaeontological Research, 1978)Item Trackways in the Stormberg(Bernard Price Institute for Palaeontological Research, 1978) van Dijk, D. E.Vertebrate trackways in the lower groups of the Karoo Supergroup are mainly pre- Beaufort fish trails, although some tetrapod trackways are known (Griffiths, 1963, p. 292; plate I; specimens in the South African Museum). Recently fish trails have been discovered in the Beaufort, for instance at Kilburn and Wagondrift, but the Beaufort, despite its rich amphibian, reptilian and synapsid fauna, is remarkable for the paucity of its vertebrate trackways. Of the Stormberg (of Lesotho) it was early noted "Fossils are comparatively rare, but reptile tracks are fairly abundant"Item Atmospheric carbon dioxide/oxygen imbalance in the late Cretaceous, hatching of eggs and the extinction of biota(Bernard Price Institute for Palaeontological Research, 1978) Oelofsen, B. W.A new theory explains why dinosaurs, pterosaurs and large avian species like Hesperornis became extinct at the end of the Cretaceous while mammals, smaller Cretaceous birds, crocodiles, chelonians and saurians survived . An atmospheric carbon dioxide/oxygen imbalance at the end of the Cretaceous caused by kimberlite volcanism, basalt flows and a reduction in oxygen production by marine phytoplankton is proposed. The unfavourable area to volume ratio of large eggs for diffusion of respiratory gases compared to that of small eggs resulted in the asphyxiation of the embryos of large endothermic egg laying groups. Endothermic species, e.g. dinosaurs that covered their eggs with soil, restricted the free circulation of air and would have been first to become extinct. Smaller ectothermic species, e.g. crocodiles, chelonians and saurians with lower embryonic respiratory requirements and endothermic species like the birds that did not cover their eggs, survived.Item The stratigraphic distribution and occurrence of South African fossil Amphibia in the Beaufort beds(Bernard Price Institute for Palaeontological Research, 1978) Kitching, J. W.A short account is given of the distribution and occurrence of fossil amphibians from the Beaufort succession, based on analyses of specimens in various South African and overseas institutions. Their occurrence is based on the re-examination of all the localities which have yielded amphibian remains to date and on field observations during the course of collecting. Attention is drawn to the paucity of fossil amphibians throughout the Beaufort palaeontological record. Possible causes of this paucity are discussed.Item A new bauriamorph from the Omingonde Formation (Middle Triassic) of South West Africa(Bernard Price Institute for Palaeontological Research, 1978) Keyser, A. W.A new genus and species of bauriamorph therapsid from the Anisian Omingonde Formation (Middle Triassic) of South West Africa is described as Herpetogale marsupialis gen. et sp. nov. This new form is chronologically the latest known member of the therocephalian lineage. It is in many ways more advanced than Bauria, but it also displays a number of more primitive features . It is advanced in its reduced postcanine series, slightly larger secondary palate, smaller suborbital fossae, and more pronounced coronoid processes of the dentaries, displaying laterally very distinct fossae maJsetericae. A very distinct crista IacialiJ is developed in front of the orbit. Primitive features are the presence of a pineal foramen and complete postorbital bars. Conspicuous and no doubt specialised are the pronounced "cheek cavities" well demarcated above by maxillary overhangs and below by shelf-like expansions on the dentaries. This arrangement suggests "cheek pouches" for food storage reminiscent of a habit in modem primates and certain rodents. The skull is complete, very little distorted or damaged, with lower jaw in occlusion. Besides an account of the cranial morphology, attention is also given to jaw musculature and the taxonomic position of the Bauriamorpha.Item Palaeoenvironmental models in the Eastern Karoo Basin(Bernard Price Institute for Palaeontological Research, 1978) Hobday, D. K.Palaeoenvironmental models are based on a three-dimensional conception of sedimentary rock units and their internal geometry. These models are process-oriented and are interpreted by comparison of their attributes with those of modern sedimentary environments. Six models are proposed as a result of observations in the eastern Karoo Basin, three in the Ecca and three in the Beaufort, although some are common to both. Both regressive delta and beach models are upward-coarsening, but they are readily distinguished on the basis of sandstone composition, texture and sedimentary structures. Beaches probably developed along a non-tidal or micro-tidal coast, but in most areas the relatively rapid sediment influx favoured the formation of deltas which prograded across the shallow shelf. Incised into the delta front sandstones are channels of distributary and alluvial origin. Large fluvial channels were generally meandering, and their deposits record a vertical reduction in flow energy from thalweg through point bar to levee, with the capping coal seams representing an hiatus in detrital sedimentation. Delta front sandstones within the Beaufort Group resemble superficially those of the Ecca, but display differences in vertical sequence which are tentatively ascribed to changes in density of the basin waters. Whereas the northern and eastern basin margins were characterized by persistent, moderate energy fluvio-deltaic sedimentation, with small prograding lobes separated by shallow embayments subject to crevasse splays, the southern part of the basin was the locus of major fluvial deposition as a consequence of orogenic uplift to the south. High energy braided stream conglomerates and sandstones were deposited contemporaneously with finer-grained meanderbelt and floodplain sediments, which accumulated farther basinward in an area of reduced gradient and more constant discharge. The value of these models is that most outcrops in the study area can be explained in terms of their relationship to one or more of the models. Future palaeoenvironmental synthesis should incorporate the great variety of biological information available from the Karoo Basin.Item Allometric growth in the Diademodontinae (Reptilia; Therapsida); a preliminary report(Bernard Price Institute for Palaeontological Research, 1978) Grine, F. E.; Hahn, B. D.The hypothesis that many, if not all, of the South African and Zambian specimens, which have been regarded as different diademodontine genera and species, actually consitute a taxonomically homogeneous, ontogenetic growth series is tested. The principles of allometric growth were applied to this sample of fossils, which varied considerably in size and shape. The approach which was followed was exclusively morphometric. The results indicate that these specimens do represent various ontogenetic stages of a growth series of only a single species of Diademodon Seeley.Item Notes on a specimen of Diademodon previously referred to Cyclogomphodon(Bernard Price Institute for Palaeontological Research, 1978) Grine, F. E.The anterior portion of the cranium of a medium-sized cynodont is described. The specimen was previously described briefly by Brink and Kitching (1953 ), who assigned it to the genus Cyclogomphodon Broom, and it was upon this specimen that they based their rediagnosis of that genus. The detailed study of this specimen has revealed that the supposed features which they considered to be generically distinctive for Cyclogomphodon either do not exist or that their validity falls away when this specimen is considered, in an ontogenetic context, as a not yet fully grown individual. It is concluded that this fossil represents a medium-sized, "juvenile", individual of DiademodonItem The advent of herbivory in certain reptilian lineages during the Triassic(Bernard Price Institute for Palaeontological Research, 1978) Gow, C. E.The dentitions of several presumed herbivorous Triassic reptiles are described and discussed. Some changes in dentitions with growth suggest that juveniles were insectivorous. The appearance of these forms may have been facilitated by floral changes which took place in the early Triassic.Item Aspects of palynology in Rhodesia(Bernard Price Institute for Palaeontological Research, 1978) Falcon, Rosemary M. S.This paper is based on a Doctoral Thesis presented to the University of the Witwatersrand, which in whole or part will be published elsewhere at greater length. The essence of the research is presented in three text figures which show the proposed correlations of Karoo strata on opposite sides of the Rhodesian palaeowatershed, correlations with Karoo-equivalent strata in other parts of Gondwanaland, and palaeofloristic trends in Rhodesia during the Permo-Triassic.