School of Geosciences
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Item A Partially Articulated Cynodont Encased in a Putative Burrow Structure from the Cynognathus Subzone C(2015-10) Afonso, NadiaA sedimentary structure containing a fossilized therapsid, and bioglyphs on the surface morphology, was found during a field expedition to Cynognathus subzone-C in the Eastern Cape, South Africa. A combination of surface scanning, petrographic thin sections, bone mapping and anatomical comparison were used to determine the deposit type and taxonomic identity of the encased therapsid, and examine the implications for biostratigraphy and faunal assemblage of the Cynognathus Assemblage Zone. The deposit is hypothesized to be a portion of a cynodont burrow (burrow margin) that was constructed in fluvial sediment near a river bank. This is the first account of a burrow in subzone-C. Pattern and directionality analysis of the bioglyphs suggest that the bioglyphs are scratch marks made by the burrower during excavation. The scratch marks are mediolaterally narrow, with some exhibiting indentation marks, indicating that the tracemaker had mediolaterally narrow unguals at the distal phalanx (claws). Anomodonts and cynodonts were common burrowers during the Triassic, however comparisons of Thrinaxodon and Lystrosaurus scratch marks to the bioglyphs on this deposit suggests that the bioglyphs were likely constructed by a cynodont as anomodont unguals are laterally wider, and are unable to create mediolaterally narrow markings. The tracemaker is hypothesized to be closely related to Thrinaxodon based on scratch mark comparison. However, bioglyph published literature is limited, and therefore the tracemaker cannot be identified. The therapsid was identified as Diademodon based on cranial and dental morphology. There is limited published literature on Diademodon constructing and/or exploiting burrows, however the taphonomy suggests that the Diademodon was near the entrance or in the tunnel of burrow nearing/during death. This is the first account of Diademodon encased in a burrow.Item On the Triggering Mechanisms of Upward Lightning(Nature Research, 2019-12) Schumann, C.; Saba, M; Warner, T.; Ferro, M.; Helsdon Jr, J.H.; Thomas, R.; Orville, R.E.Upward lightning studies took place in Rapid City, South Dakota, USA and S. Paulo, Brazil during the summer thunderstorm seasons from 2011 to 2016. One of the main objectives of these campaigns was to evaluate and characterize the triggering of upward positive leaders from tall objects due to preceding nearby flash activity. 110 upward flashes were observed with a combination of high- and standard-speed video and digital still cameras, electric field meters, fast electric-field antenna systems, and for two seasons, a Lightning Mapping Array. These data were analyzed, along with correlated lightning location system data, to determine the triggering flash type responsible for the initiation of upward leaders from towers. In this paper, we describe the various processes during flash activity that can trigger upward leaders from tall objects in the USA and in Brazil. We conclude that the most effective triggering component is the propagation of the in-cloud negative leader during the continuing current that follows a positive return stroke.Item Reappraisal of the envenoming capacity of Euchambersia mirabilis (Therapsida, Therocephalia) using μcT-scanning techniques.(Public Library of Science, 2017-02) Benoit, J.; Norton, L.A.; Manger, P.R.; Rubidge, B.S.Euchambersia mirabilis is an iconic species of Permo-Triassic therapsid because of its unusually large external maxillary fossa linked through a sulcus to a ridged canine. This anatomy led to the commonly accepted conclusion that the large fossa accommodated a venom gland. However, this hypothesis remains untested so far. Here, we conducted a μCT scan assisted reappraisal of the envenoming capacity of Euchambersia, with a special focus on the anatomy of the maxillary fossa and canines. This study shows that the fossa, presumably for the venom-producing gland, is directly linked to the maxillary canal, which carries the trigeminal nerve (responsible for the sensitivity of the face). The peculiar anatomy of the maxillary canal suggests important reorganisation in the somatosensory system and that a ganglion could possibly have been present in the maxillary fossa instead of a venom gland. Nevertheless, the venom gland hypothesis is still preferred since we describe, for the first time, the complete crown morphology of the incisiform teeth of Euchambersia, which strongly suggests that the complete dentition was ridged. Therefore Euchambersia manifests evidence of all characteristics of venomous animals: a venom gland (in the maxillary fossa), a mechanism to deliver the venom (the maxillary canal and/or the sulcus located ventrally to the fossa); and an apparatus with which to inflict a wound for venom delivery (the ridged dentition).Item Oxygen isotopes suggest elevated thermometabolism within multiple permo-triassic therapsid clades(eLife Sciences Publications Ltd, 2017-07) Rey, K.; Amiot, R.; Fourel, F.; Abdala, F.; Fluteau, F.; Jalil, N.-E.; Liu, J.; Rubidge, B.S.; Smith, R.M.H.; Steyer, J.S.; Viglietti, P.A.; Wang, X.; Lécuyer, C.The only true living endothermic vertebrates are birds and mammals, which produce and regulate their internal temperature quite independently from their surroundings. For mammal ancestors, anatomical clues suggest that endothermy originated during the Permian or Triassic. Here we investigate the origin of mammalian thermoregulation by analysing apatite stable oxygen isotope compositions (d18Op) of some of their Permo-Triassic therapsid relatives. Comparing of the d18Op values of therapsid bone and tooth apatites to those of co-existing non-therapsid tetrapods, demonstrates different body temperatures and thermoregulatory strategies. It is proposed that cynodonts and dicynodonts independently acquired constant elevated thermometabolism, respectively within the Eucynodontia and Lystrosauridae + Kannemeyeriiformes clades. We conclude that mammalian endothermy originated in the Epicynodontia during the middle-late Permian. Major global climatic and environmental fluctuations were the most likely selective pressures on the success of such elevated thermometabolism.Item Arrested development-A comparative analysis of multilayer corona textures in high-grade metamorphic rocks(European Geosciences Union (EGU), 2017-02) Ogilvie, P.; Gibson, R.L.Coronas, including symplectites, provide vital clues to the presence of arrested reaction and preservation of partial equilibrium in metamorphic and igneous rocks. Compositional zonation across such coronas is common, indicating the persistence of chemical potential gradients and incomplete equilibration. Major controls on corona mineralogy include prevailing pressure (P), temperature (T ) and water activity (aH2O) during formation, reaction duration (t ) single-stage or sequential corona layer growth; reactant bulk compositions (X) and the extent of metasomatic exchange with the surrounding rock; relative diffusion rates for major components; and/or contemporaneous deformation and strain. High-variance local equilibria in a corona and disequilibrium across the corona as a whole preclude the application of conventional thermobarometry when determining P-T conditions of corona formation, and zonation in phase composition across a corona should not be interpreted as a record of discrete P-T conditions during successive layer growth along the P-T path. Rather, the local equilibria between mineral pairs in corona layers more likely reflect compositional partitioning of the corona domain during steadystate growth at constant P and T . Corona formation in pelitic and mafic rocks requires relatively dry, residual bulk rock compositions. Since most melt is lost along the high-T prograde to peak segment of the P-T path, only a small fraction of melt is generally retained in the residual post-peak assemblage. Reduced melt volumes with cooling limit length scales of diffusion to the extent that diffusion-controlled corona growth occurs. On the prograde path, the low melt (or melt-absent) volumes required for diffusion-controlled corona growth are only commonly realized in mafic igneous rocks, owing to their intrinsic anhydrous bulk composition, and in dry, residual pelitic compositions that have lost melt in an earlier metamorphic event. Experimental work characterizing rate-limiting reaction mechanisms and their petrogenetic signatures in increasingly complex, higher-variance systems has facilitated the refinement of chemical fractionation and partial equilibration diffusion models necessary to more fully understand corona development. Through the application of quantitative physical diffusion models of coronas coupled with phase equilibria modelling utilizing calculated chemical potential gradients, it is possible to model the evolution of a corona through P-T-X-t space by continuous, steady-state and/or sequential, episodic reaction mechanisms. Most coronas in granulites form through a combination of these endmember reaction mechanisms, each characterized by distinct textural and chemical potential signatures with very different petrogenetic implications. An understanding of the inherent petrogenetic limitations of a reaction mechanism model is critical if an appropriate interpretation of P-T evolution is to be inferred from a corona. Since corona modelling employing calculated chemical potential gradients assumes nothing about the sequence in which the layers form and is directly constrained by phase compositional variation within a layer, it allows far more nuanced and robust understanding of corona evolution and its implications for the path of a rock in P-T-X space.Item A decorated raven bone from the Zaskalnaya VI (Kolosovskaya) Neanderthal site, Crimea(Public Library of Science, 2017-03) Majkic, A.; Evans, S.; Stepanchuk, V.; Tsvelykh, A.; D'Errico, F.We analyze a radius bone fragment of a raven (Corvus corax) from Zaskalnaya VI rock shelter, Crimea. The object bears seven notches and comes from an archaeological level attributed to a Micoquian industry dated to between 38 and 43 cal kyr BP. Our study aims to examine the degree of regularity and intentionality of this set of notches through their technological and morphometric analysis, complemented by comparative experimental work. Microscopic analysis of the notches indicate that they were produced by the to-and-fro movement of a lithic cutting edge and that two notches were added to fill in the gap left between previously cut notches, probably to increase the visual consistency of the pattern. Multivariate analysis of morphometric data recorded on the archaeological notches and sets of notches cut by nine modern experimenters on radii of domestic turkeys shows that the variations recorded on the Zaskalnaya set are comparable to experimental sets made with the aim of producing similar, parallel, equidistant notches. Identification of the Weber Fraction, the constant that accounts for error in human perception, for equidistant notches cut on bone rods and its application to the Zaskalnaya set of notches and thirty-six sets of notches incised on seventeen Upper Palaeolithic bone objects from seven sites indicate that the Zaskalnaya set falls within the range of variation of regularly spaced experimental and Upper Palaeolithic sets of notches. This suggests that even if the production of the notches may have had a utilitarian reason the notches were made with the goal of producing a visually consistent pattern. This object represents the first instance of a bird bone from a Neanderthal site bearing modifications that cannot be explained as the result of butchery activities and for which a symbolic argument can be built on direct rather than circumstantial evidence.Item Osteopathology and insect traces in the Australopithecus africanus skeleton StW 431(Academy of Science of South Africa (ASSAf), 2017-01) Zipfel, B.; Jakata, K.; Bonney, H.; Odes, E.J.; Parkinson, A.H.; Randolph-Quinney, P.S.; Berger, L.R.We present the first application of high-resolution micro computed tomography in an analysis of both the internal and external morphology of the lumbar region of StW 431 - a hominin skeleton recovered from Member 4 infill of the Sterkfontein Caves (South Africa) in 1987. The lumbar vertebrae of the individual present a number of proliferative and erosive bony processes, which were investigated in this study. Investigations suggest a complex history of taphonomic alteration to pre-existing spinal degenerative joint disease (SDJD) as well as post-mortem modification by an unknown insect. This study is in agreement with previous pathological diagnoses of SDJD which affected StW 431 and is the first time insect traces on this hominin are described. The results of this analysis attest to the complex series of post-mortem processes affecting the Sterkfontein site and its fossil assemblages.Item Potential for identifying plant-based toxins on San hunter-gatherer arrowheads(Academy of Science of South Africa (ASSAf), 2017-03) Wooding, M.; Bradfield, J.; Maharaj, V.; Koot, D.; Wadley, L.; Prinsloo, L.; Lombard, M.The antiquity of the use of hunting poisons has received much attention in recent years. In this paper we present the results of a pilot study designed to detect the presence of organic compounds, typically of less than 1200 Da, from poisonous plants that may have been used as hunting poisons in the past. We used ultra-performance liquid chromatography connected to a Synapt G2 high-resolution MS-QTOF mass spectrometer (UPLC-QTOF-MS) to provisionally identify plant-based toxins present in (1) extracts of fresh plant material, (2) a blind control recipe consisting of three plant ingredients and (3) a Hei||om arrow poison of unknown ingredients. Although not all expected toxic compounds were identified, those that were identified compared favourably with those reported in the literature and confirmed through databases, specifically the Dictionary of Natural Products and ChemSpider. MS/MS fragmentation patterns and accurate mass were used for tentative identification of compounds because archaeological residues usually contain insufficient material for unambiguous identification using nuclear magnetic resonance. We highlight the potential of this method for accurately identifying plant-based toxins present on archaeological artefacts and unique (albeit non-toxic) chemical markers that may allow one to infer the presence of toxic plant ingredients in arrow poisons. Any chemical study of archaeological material should consider the unique environmental degradative factors and be sensitive to the oxidative by-products of toxic compounds.Item A probabilistic definition of a species, fuzzy boundaries and 'sigma taxonomy'(Academy of Science of South Africa (ASSAF)., 2017-05) Schrein, C.M.; Thackeray, J.F.No abstract available.Item Patterns of change and continuity in ochre use during the late Middle Stone Age of the Horn of Africa: The Porc-Epic Cave record(Public Library of Science, 2017-05) Rosso, D. E.; D'Errico, F.; Queffelec, A.Ochre is found at numerous Middle Stone Age (MSA) sites and plays a key role in early modern human archaeology. Here we analyse the largest known East African MSA ochre assemblage, comprising 40 kg of ochre, found at Porc-Epic Cave, Ethiopia, spanning a period of at least 4,500 years. Visual characterisation of ochre types, microscopic identification of traces of modification, morphological and morphometric analysis of ochre pieces and modified areas, experimental reproduction of grinding processes, surface texture analysis of archaeological and experimentally ground ochre facets, laser granulometry of ochre powder produced experimentally on different grindstones and by Hamar and Ovahimba women from Ethiopia and Namibia respectively, were, for the first time, combined to explore diachronic shifts in ochre processing technology. Our results identify patterns of continuity in ochre acquisition, treatment and use reflecting both persistent use of the same geological resources and similar uses of iron-rich rocks by late MSA Porc-Epic inhabitants. Considering the large amount of ochre processed at the site, this continuity can be interpreted as the expression of a cohesive cultural adaptation, largely shared by all community members and consistently transmitted through time. A gradual shift in preferred processing techniques and motions is interpreted as reflecting cultural drift within this practice. Evidence for the grinding of ochre to produce small quantities of powder throughout the sequence is consistent with a use in symbolic activities for at least part of the ochre assemblage from Porc-Epic Cave.