P. John Hancox

Cynodonts from the Uppermost Burgersdorp Formation, South Africa, and their bearing on the biostratigraphy and correlation of the Triassic Cynognathus Assemblage Zone

Abstract The Burgersdorp Formation in the Beaufort Group of the South African Karoo Basin records a diverse and rich vertebrate fauna that is referred biostratigraphically to the Cynognathus Assemblage Zone. Recent collecting efforts, and taxonomic and biostratigraphic studies on this formation, resulted in a proposed subdivision of the Cynognathus Assemblage Zone into three subzones informally known as A, B, and C. Cynodont fossils constitute an important component of the fauna of the uppermost subzone C of the Cynognathus Assemblage Zone. As in the middle subzone B, cynognathids, diademodontids, and trirachodontids are represented in subzone C, although the latter group–instead of Diademodon–is the dominant taxon. The presence of Cynognathus in the faunas of the three subzones confirms that this genus is the correct choice as the index taxon of the assemblage zone. The large size attained by trirachodontid specimens from subzone C represents an unusual characteristic. One complete skull measured 160 mm in length, although fragmentary remains of other specimens indicate even larger sizes. These skull lengths are well above the 100 mm that characterize trirachodontids recovered from the older subzones A and B. The large size, and particularly the ovoid overall pattern of the upper gomphodont postcanines allows the assignment of the trirachodontid specimens from subzone C to Cricodon metabolus, previously known from the Manda Formation in Tanzania. The Cynognathus Assemblage Zone of South Africa is shown to be the most temporally complete Early-Middle Triassic nonmarine sequence in southern Gondwana, and is the template against which other sequences of similar age may be compared.

Basin development during the deposition of the Elliot Formation (Late Triassic - Early Jurassic), Karoo Supergroup, South Africa

The integrated results of a facies analysis and provenance study of the Late Triassic to Early Jurassic Elliot Formation (Karoo Supergroup) provide some new insights into the development of the main Karoo foreland system of South Africa. Based on changes in the fluvial style, palaeocurrent pattern, provenance, isopach trends and fossil content, a regional lithostratigraphic subdivision of the Elliot Formation is proposed. In addition, the boundary between the Lower and Upper Elliot formations appears to be a second order sequence boundary. This unconformity was probably generated by the last stage of orogenic loading of the Cape Fold Belt, which interrupted the overall, first order orogenic unloading of the system, suggesting that tectonically controlled flexural subsidence existed in the main Karoo Basin until at least the end of Triassic. The magnitude of this pre-Upper Elliot tectonic event is signified by the presence of outsized quartzite pebbles and boulders, believed to have originated in the Cape Fold Belt. A number of tectonic structures, e.g. pene-contemporaneous normal faults and large-scale convolute bedding, coupled to sandstones with basement uplift/craton interior provenance, and easterly palaeocurrent direction for the Upper Elliot Formation suggest that the first stages of inversion from a compressional to extensional tectonic regime began only in the Early Jurassic.

New mastodonsaurid temnospondyls from the Cynognathus Assemblage Zone (Upper Beaufort Group; Karoo Basin) of South Africa

Abstract Two new mastodonsaurid temnospondyls are described from the Early to Middle Triassic Cynognathus Assemblage Zone of the Upper Beaufort Group (Karoo Basin) of South Africa. Paracyclotosaurus morganorum, sp. nov. is based on a partial skull from the uppermost part of the Cynognathus Assemblage Zone (Subzone C; late Anisian) in the southern Karoo Basin, and is the first occurrence of the genus Paracyclotosaurus outside of India and Australia. Jammerbergia formops, gen. et sp. nov. is based on a partial skull, presumably from Subzone B (early Anisian) of the Cynognathus Assemblage Zone, and is distinctive in its unique suite of primitive and derived characters. Although the intrarelationships of mastodonsaurids remain largely unresolved, the two most recent analyses are similar in the identification of an ‘advanced’ mastodonsaurid clade whose members are characterized by laterally directed tabular horns. Jammerbergia probably belongs within this clade, albeit within a basal position. Jammerbergia and Paracyclotosaurus share the synapomorphy of large, antero-posteriorly expanded tabulars, and may represent sister taxa. The Cynognathus Assemblage Zone is characterized by three subzones of differing ages and faunas, with no overlap in the temnospondyls between the subzones.

Angonisaurus and Shansiodon, Dicynodonts (Therapsida, Anomodontia) from Subzone C of the Cynognathus Assemblage Zone (Middle Triassic) of South Africa

ABSTRACT Dicynodonts are the most abundant therapsids from the Beaufort Group (Karoo Basin, South Africa), and they have been used as index fossils to define most of the Beaufort biozones. Although speciose during the Late Permian, dicynodont diversity was greatly reduced by the end-Permian mass extinction. The Cynognathus Assemblage Zone, the uppermost biozone of the Beaufort Group, is traditionally known to host only the dicynodonts Kannemeyeria simocephalus and Kombuisia frerensis. Recent biostratigraphic research in this biozone has revealed the presence of two more poorly known dicynodont genera, Angonisaurus and Shansiodon, which are biostratigraphically constrained to the uppermost Cynognathus Assemblage Zone (subzone C). Although these taxa have been reported from subzone C of the Cynognathus Assemblage Zone previously, we provide the first detailed description of the material in question and justifications for the taxonomic identifications. The presence of Angonisaurus in the Cynognathus subzone C allows a direct correlation between this assemblage and that of the Lifua Member of the Manda beds in Tanzania. A correlation with the Antarctic upper Fremouw Formation also may be possible, but is less certain. The presence of Shansiodon allows a direct correlation with the upper Ermaying Formation of China, but we reject the previously proposed global ‘Shansiodon biochron’ because Shansiodon sensu stricto only occurs in China and South Africa. Biogeographically, Angonisaurus appears to have been widespread but rare in southern Gondwana, and the unusual distribution of Shansiodon mirrors that of Diictodon feliceps in the Permian. Southern African dicynodont assemblages display increased provinciality in the Middle Triassic.

The contact of the Molteno and Elliot formations through the main Karoo Basin, South Africa: a second-order sequence boundary

The Late Triassic to Early Jurassic Molteno, Elliot and Clarens formations of the uppermost part of the Karoo Supergroup in the main Karoo Basin of South Africa form a distinct tectono-sedimentary sequence. A major problem with the modeling of this part of the Karoo basinal fill is that the nature of the Molteno-Elliot contact is poorly understood. Previously the contact has been defined on a mix of lithological and palaeontological criteria, and has been considered to be gradational or transitional in nature, with the Elliot considered the distal equivalent of the upper Molteno Formation. Recent field investigations demonstrate that the boundary can be defined on lithologic changes, including the gross and internal geometries of the sandstone units and contained lithofacies associations, the presence/absence of coal seams and paleosols, and on palaeocurrent patterns, sandstone composition and grain-size variations. This boundary represents a regional unconformity throughout the basin and the recognition of this cryptic second order sequence boundary invalidates previous interpretations of an interfingering stratigraphic relationship between the two formations. Stacking patterns in the upper Karoo Supergroup, and the tectonic framework of their development, suggest that the southern margin of the Kaapvaal Craton acted as a regional control on sequence development during Late Triassic - Early Jurassic times.

A New Species of Garjainia Ochev, 1958 (Diapsida: Archosauriformes: Erythrosuchidae) from the Early Triassic of South Africa

A new species of the erythrosuchid archosauriform reptile Garjainia Ochev, 1958 is described on the basis of disarticulated but abundant and well-preserved cranial and postcranial material from the late Early Triassic (late Olenekian) Subzone A of the Cynognathus Assemblage Zone of the Burgersdorp Formation (Beaufort Group) of the Karoo Basin of South Africa. The new species, G. madiba, differs from its unique congener, G. prima from the late Olenekian of European Russia, most notably in having large bony bosses on the lateral surfaces of the jugals and postorbitals. The new species also has more teeth and a proportionately longer postacetabular process of the ilium than G. prima. Analysis of G. madiba bone histology reveals thick compact cortices comprised of highly vascularized, rapidly forming fibro-lamellar bone tissue, similar to Erythrosuchus africanus from Subzone B of the Cynognathus Assemblage Zone. The most notable differences between the two taxa are the predominance of a radiating vascular network and presence of annuli in the limb bones of G. madiba. These features indicate rapid growth rates, consistent with data for many other Triassic archosauriforms, but also a high degree of developmental plasticity as growth remained flexible. The diagnoses of Garjainia and of Erythrosuchidae are addressed and revised. Garjainia madiba is the geologically oldest erythrosuchid known from the Southern Hemisphere, and demonstrates that erythrosuchids achieved a cosmopolitan biogeographical distribution by the end of the Early Triassic, within five million years of the end-Permian mass extinction event. It provides new insights into the diversity of the Subzone A vertebrate assemblage, which partially fills a major gap between classic ‘faunal’ assemblages from the older Lystrosaurus Assemblage Zone (earliest Triassic) and the younger Subzone B of the Cynognathus Assemblage Zone (early Middle Triassic).

The origin and development of the Nyl River floodplain wetland, Limpopo Province, South Africa: trunk-tributary river interactions in a dryland setting

The Nyl River floodplain wetland, one of South Africas largest floodplain wetlands and a Ramsar site of international conservation importance, is located in an area of long-term and still active valley sediment accumulation. Creation of accommodation space for sedimentation has previously been attributed to tectonic controls, but new investigations reveal that a more likely cause is progradation of coarse-grained tributary fans across the narrow river valley downstream of the main area of floodplain wetland. Obstruction of trunk river flow and sediment transfer by these tributary fans has led to backponding and upstream gradient reduction and to accumulation of valley fills up to ∼35 m thick. Chronological control for the timing and rate of sediment accumulation is limited, but we hypothesise that a semi-arid to arid climate, characterised by asynchronous trunk–tributary activity that results in marked discontinuities in downstream water and sediment transfer, is likely to have been a key control. These interpretations are supported by other studies of dryland rivers globally and the findings add to our growing understanding of the controls on the origin and development of southern African wetlands, particularly by demonstrating how the combination of a particular physiography and a dryland climate can impart some distinctive geomorphological characteristics.

Advances in Nonmarine Karoo Biostratigraphy: Significance for Understanding Basin Development

The nonmarine Permo-Jurassic deposits of the Karoo Supergroup of South Africa have long been a world standard for tetrapod biostratigraphy. Recent and ongoing research is revising the palaeoflora and palaeofauna of these sedimentary strata with an unprecedented level of stratigraphic precision. This work has shown that: Permian palynomorphs are useful for correlating time-equivalent lithostratigraphic units in different sectors of the basin; that there is a marked end-Guadalupian diversity drop in tetrapods; that the Dicynodon Assemblage Zone can be subdivided, and should be renamed as the Daptocephalus Assemblage Zone; that the Cynognathus Assemblage Zone has a robust threefold subdivision; and that the name Euskelosaurus for the Euskelosaurus Range Zone is invalid and should be replaced. This work, together with new radiometric dates from the Karoo Supergroup, has dramatically enhanced our understanding of the timing of major evolutionary events in terrestrial ecosystems and provides strong evidence for tectonic controls on accommodation and sedimentation in the Karoo Basin during the Permo-Jurassic, within an overall flexural basinal setting.

The Earliest Post-Paleozoic Freshwater Bivalves Preserved in Coprolites from the Karoo Basin, South Africa

Background Several clades of bivalve molluscs have invaded freshwaters at various times throughout Phanerozoic history. The most successful freshwater clade in the modern world is the Unionoida. Unionoids arose in the Triassic Period, sometime after the major extinction event at the End-Permian boundary and are now widely distributed across all continents except Antarctica. Until now, no freshwater bivalves of any kind were known to exist in the Early Triassic. Principal Findings Here we report on a faunule of two small freshwater bivalve species preserved in vertebrate coprolites from the Olenekian (Lower Triassic) of the Burgersdorp Formation of the Karoo Basin, South Africa. Positive identification of these bivalves is not possible due to the limited material. Nevertheless they do show similarities with Unionoida although they fall below the size range of extant unionoids. Phylogenetic analysis is not possible with such limited material and consequently the assignment remains somewhat speculative. Conclusions Bivalve molluscs re-invaded freshwaters soon after the End-Permian extinction event, during the earliest part of the recovery phase during the Olenekian Stage of the Early Triassic. If the specimens do represent unionoids then these Early Triassic examples may be an example of the Lilliput effect. Since the oldest incontrovertible freshwater unionoids are also from sub-Saharan Africa, it is possible that this subcontinent hosted the initial freshwater radiation of the Unionoida. This find also demonstrates the importance of coprolites as microenvironments of exceptional preservation that contain fossils of organisms that would otherwise have left no trace.

Complex Multicusped Postcanine Teeth from the Lower Triassic of South Africa

ABSTRACT Two incisors and five postcanine teeth of complex crown morphology were found in the lower levels of the Burgersdorp Formation of the Beaufort Group, corresponding to the basal Subzone A of the Cynognathus Assemblage Zone (late Olenekian). All the teeth bear a single root and the postcanines show two rows of mesiodistally aligned cusps and a central basin or groove. Among the postcanines, two general patterns of crown morphology are recognized on the basis of relative length of the cusp rows, number of cusps per row, and width of the central area. Phylogenetic affinities of the described specimens remain unclear, and thus they are regarded as Eucynodontia incertae sedis. However, comparisons with non-mammalian cynodonts with labiolingually expanded postcanines show that they are most similar to those of Aleodon, Candelariodon, and some haramiyids. Many cynodont taxa such as Aleodon, Candelariodon, Cromptodon, haramiyids, and tritylodontids, which are probably not closely related to each other, have labiolingually expanded postcanines with cusps arranged mesiodistally in rows and a central basin; thus pointing to the homoplastic nature of dental morphologies in the cynodont lineage. The teeth presented here are the oldest record of therapsid teeth with crowns having parallel rows of cusps, representing a temporal extension of approximately 10 million years for this crown pattern.