Heritage Cases

The Lystrosaurus declivis Assemblage Zone (LAZ) has its type section in the South African Karoo Basin (Botha and Smith, 2020) and represents approximately one million years (Induan age 251.9 -251.2Ma) when the global sedimentological and fossil record shows the ancient intracontinental lowlands of southern Gondwana were subjected to prolonged climatic warming (hyperthermal) and the onset of a monsoonal rainfall regime. We now need to understand just how severely the terrestrial ecosystems of these low-lying land areas, including the Karoo Basin, were affected by these conditions, and in particular how the various tetrapod lineages survived at the different latitudes (Gastaldo et al., 2020). One of the therapsid clades, the Cynodontia, continued to flourish in this drought-stricken environment and went on to give rise to the first mammals during the Late Triassic. Another lineage, the archosaurs, also began their radiation and rise to global dominance in this post-extinction hyperthermic world and the temnospondyls appear to have begun a surge in speciation. A key research question is whether it was the ability of representatives of these clades to opportunistically adapt, or their pre-existing drought tolerance that allowed them to flourish under these conditions. The LAZ of the Karoo Basin is a biostratigraphic unit characterized by fossils that have long been regarded as post- apocalyptic “disaster taxa” that co-existed for a geologically short time period (Botha and Smith, 2006; Viglietti et al., 2021). This interval represents a global biostratigraphic time marker for the earliest Triassic Period (Scythian epoch- Induan age). Similar taxa have been identified from Karoo equivalent strata in Brazil (Souto-Ribeiro and Holz, 1998), Antarctica (Collinson at al., 2006), India (Bandyopadhyay et al., 2002) , Russia (Benton et al., 2004), China (Chen and Benton, 2012), and most recently Mozambique (Araujo et al., 2020), which makes any new information derived from studies in the Karoo Basin immediately applicable to these other occurrences. Moreover, the End-Permian mass extinction, widely accepted as marking the base of the LAZ, has been radiometrically-dated from zircons extracted from the Chinese marine sequences at 251.9 +/- 0.1 Mya (Burgess et al., 2014). This three-year project proposal is subdivided into five self-contained yet inter-related topics that, in the final synthesis, will coalesce to form a comprehensive description of the dynamics of the post-extinction terrestrial ecosystem of the earliest Triassic Karoo. The individual topics are as follows: 1. Revised biostratigraphic ranges and population densities of Lystrosaurus declivis Assemblage Zone (LAZ) taxa with an evaluation of their status as disaster taxa. This topic is an international endeavour led by R Smith (ESI Wits and Iziko Museum, Cape Town) and J Botha (National Museum, Bloemfontein) with collaboration from Pia Viglietti (Field Museum, Chicago) and Julien Benoit (ESI, Wits) and identifications by Ken Angielczyk (Field Museum Chicago), Adam Huttenlocker (Univ Southern California, Los Angeles ), Christian Kammerer (North Carolina Museum of Natural Sciences, Raleigh), Fernando Abdala (CONICET, Tucaman) and Claudia Marsicano (CONICET, Univ Buenos Aries) The LAZ outcrops throughout most of the central and western Karoo Basin with a few fossil-bearing outcrops in the Eastern Cape and Kwa-Zulu Natal. The biozone reaches a maximum thickness of 700m in the Katberg Pass area, thinning northwards to 400m in the Cradock/ Graaff Reinet districts and 250m in the Bethulie districts (Botha and Smith, 2020). We will consolidate our field dataset concentrating on the LAZ at several historical and new study localities in the Sarah Baartman/Graaff Reinet (Leeufontein, Lootsberg Pass/ Old Wapadsberg) and Xhariep/Bethulie (Nooitgedaght, Donald, Heldemoed, Bethel and Caledondraai) districts. As part of this topic there will be a special investigation of the specimens reported by Kitching (1968) of Permian tetrapod taxa collected from localities yielding Triassic LAZ taxa with a view to resolving whether they are of late-surviving taxa or the fossils have been “reworked”or if there is some other geological explanation. Expected outcome: Provisional title for peer reviewed publication – Re-appraisal of the lower Lystrosaurus Assemblage Zone in the Karoo Basin as a disaster assemblage. 2. Field evidence of recurrent drought episodes in the Karoo Basin during the Early Triassic hyperthermal. This topic will be led by R Smith and C Browning (Iziko Museums, Cape Town) with collaboration from Pia Viglietti (Field Museum, Chicago). . Gestaldo et al. (2020) used isotope geochemistry of the pedogenic nodule conglomerates in the Early–Mid Triassic strata of the Karoo Basin to plot climatic wet/dry oscillations. Retallack (2021) used stable isotopes and depth to calcic horizons in the same sections to define similar climatic pertubations, however, they do not co-incide with those of Gastaldo et al. (2020). We propose to test these findings with more detailed field investigation of the sedimentology, vertebrate taphonomy and ichnology of the wet/dry phases. Some of the fieldwork for this paper has already been completed under the PTB extinction project, however, there is a need for further sedimentological evidence of the palaeoclimate and floodplain surface processes with particular emphasis on determining the rainfall regime, the river flood hydrology and the sites of tetrapod bone accumulation and burial. This is best effected by planimetric mapping and taphonomic analysis of numerous in situ skeletons at the Bethulie and Graaff Reinet study sites. The dense monotaxic Lystrosaurus bonebeds have been interpreted variously as drought accumulations (Smith and Botha 2005) or victims of sudden cold-spells (Viglietti et al., 2014). Some rare specimens in this site appear to have fossilised skin impressions that are tentatively interpreted as desiccated, naturally mummified carcasses. These specimens need further preparation, U-V light imaging and possibly Micro-CT scanning to strengthen this interpretation. Expected outcomes: Provisional titles for peer-reviewed publications Concentrations of Lystrosaurus carcasses on the floodplains of the Early Triassic Karoo Basin- entrapment, deluge or drought? Sedimentological and taphonomic evidence of recurrent drought in the earliest Triassic Karoo Basin, South Africa 3. Karoo tetrapod survival strategies following the end-Permian mass extinction in the Karoo Basin A multidisciplinary study led by J Botha (National Museum, Bloemfontein) and R Smith with collaboration of J Benoit (ESI, Wits.) The study will focus on the observed increase in frequency of burrow casts in strata associated with the extinction (pre- and post). Recent research has indicated oscillations between aridity and humidity during the EPME (Retallack, 2021). There is a temptation to interpret changes in the abundance of burrows as directly reflecting a behavioural response to rapid climate change; in this case to extremes of diurnal and seasonal temperatures and humidity. However there may also be a sedimentological control over the preservation that could account for this increased preservation that is unrelated to changes in burrowing frequency. To help resolve this uncertainty, we aim to excavate a few complete in situ burrow systems from the Bethulie and Graaff Reinet study sites. In doing so we will accurately survey the casts (in 3-D), and prepare all fossil bones that are found preserved inside for clues as to the diggers, the occupants, and the reason for going underground. We will also record the presence of burrows onto our sedimentological logs to determine if the frequency of burrows changes with the oscillations between aridity and humidity as dictated in Retallack (2021). A more direct approach to determining whether Lystrosaurus practiced aestivation and/or cold torpor as a physiological survival mechanism is to look at the pattern of growth increments in the dentine of their tusks. A pilot study has already shown positive results for Antarctic specimens (i.e., Whitney and Sidor, 2020) which will be expanded and improved upon by co-investigator J. Botha, a specialist in Karoo palaeohistology based at the National Museum, Bloemfontein. In situ Lystrosaurus will be specifically collected in order to have a stratigraphical context to determine if Lystrosaurus individuals showed oscillations/changes in their teeth according to the arid/humid oscillations outlined by Retallack (2021). We will positively identify the material to species level in order to rule out possible inter-specific variation. Dr Julien Benoit will be augmenting these findings with Micro-CT scans of a growth series of Lystrosaurus murrayi currently on display in the Origins Centre, University of the Witwatersrand. It is hoped that a combination of these two methods and a better understanding of the environmental conditions might help us understand why limb bones of even the largest post extinction Lystrosaurus lack the histological signature of asymptotic growth (Botha, 2020). Expected outcome: Provisional title of peer-reviewed publication; Juvenile aggregation and aestivation/torpor as survival behaviours for Lystrosaurus in the earliest Triassic Karoo Basin, South Africa. 4. Niche-partitioning of small-bodied faunivores in the Early Triassic Karoo ecosystem? An interdisciplinary topic led by R Smith with collaboration from Claire Browning (Iziko Museums), Lutendo Mukwevho (ESI Wits Honours student) and Julien Benoit( ESI Wits) How a number of small faunivores prevented competition for resources is a difficult question to answer in the absence of direct evidence such as stomach contents, predation traces (e.g. tooth marks) and coprolites. We are fortunate to have recovered two therocephalian specimens, seemingly of the same genus, with unequivocal fossilized stomach contents. Full detailed analysis of these specimens, augmented with Micro CT imaging, will give us evidence of at least one of the small predator/prey relationships that characterize this time interval. (Lutendo Mukwevho, R Smith) Another line of investigation to determine palaeo-diet is to analyse the micro-wear structure in tooth enamel. These are best imaged with scanning electron microscope and laser scanner. The source of well-prepared specimens will likely be the collections at Iziko SA Museum where a suitable SEM machine is already available and laser scans can be done in collaboration with colleagues at UCT. Claire Browning, Iziko’s curator of Karoo Palaeontology is experienced in SEM imaging and well-positioned to lead this topic. There is circumstantial evidence to suggest that insects were not significantly affected by the extinction event such that they may well have become a more important food source for the small faunivores in the aftermath. This project will investigate the invertebrate trace fossils that are a prominent feature of the upper Palingkloof Member (0-20m above the Daptocephalus AZ/LAZ boundary) crevasse splay sandstones to provide more support for this hypothesis (C. Browning, R. Smith). Nocturnal hunting is a strategy employed by many mammals in the modern savanna and it is possible that this was adopted by small faunivores in the Early Triassic Karoo. An anatomical indicator for this behaviour is a relative increase in olfactory, tactile and auditory capabilities manifesting in the skull. A survey of the existing Micro-CT scans of small faunivore skulls of the Early Triassic in the regions of the olfactory bulbs, maxillary canal and bony labyrinth may yield evidence of the size of the olfactory lobes of the brain, the presence of a trigeminal nerve and the architecture of the inner ear respectively. These features may highlight taxa with nocturnal traits (J Benoit, C Browning). Expected outcome: Provisional titles for peer-reviewed publications. Fossilised stomach contents reveal the diet of an Early Triassic therocephalian during the post-extinction hyperthermal in the Karoo Basin, South Africa Tooth microwear patterns confirm insectivory as the staple diet of the Early Triassic faunivores in the Karoo Basin. South Africa Ichnological evidence of insect diversity in the post-extinction earliest Triassic Karoo Basin South Africa 5. The positioning of the Permo-Triassic boundary in the Karoo Supergroup of South Africa: a multi-disciplinary approach. Led by J Botha(National Museum, Bloemfontein), in collaboration with R Smith, P Viglietti (Field Museum Chicago), A Huttenlocker(Univ. Southern California, Los Angeles ) This topic directly addresses the discrepancy between the biostratigraphic and chronostratigraphic placement of the PTB in the main Karoo Basin. Recently Gastaldo et al. (2020) published a radiometric date from a reported ash bed from the basalmost Lystrosaurus Assemblage Zone that contradicts our results (Botha et al., 2020). Gastaldo et al.’s (2020) IC-PMS -TIMS date of 252.24Ma for reportedly volcanic ash-sourced zircons at the top of the Palingkloof Member would place the 251.9Ma level (PTB) into f the Katberg Formation (some 15-25 metres higher in the stratigraphic column than the biostratigraphically-defined extinction that has been positioned by the last appearance datums of numerous tetrapod taxa. In contrast, a detrital zircon maximum date of 251.7+/- 0.3 Ma from a sandstone some 8m below the extinction interval was reported by Botha et al. (2020) which is within the margin of error for the Karoo tetrapod extinction and the PTB being synchronous. These zircon populations yield an age range consistent with the traditional placement of the PTB within the Palingkloof member, and call into question Gastaldo’s (2020) alternative hypothesis of a Permian age for the basalmost Katberg Formation. Although our latest work suggests that the total land extinction was likely of longer duration than the marine extinction (see Viglietti et al., 2021), the question of whether the main tetrapod extinction in the Karoo is either wholly or partially synchronous, or completely asynchronous, with the Permo-Triassic boundary (and the marine extinction) still remains unresolved. An ideal solution would be to extract zircons from a sequence of volcanic airfall ash-beds through the +/-50m interval in-question, however, all workers agree that primary tuffs are so scarce that finding more than one in this 50m interval is unlikely. We will however sample all potential ash beds, including the Gastaldo et al. (2020) tuff, and test for reproducibility of results. The sample from this horizon is already with one of our collaborators, Dr Pia Viglietti in the USA, and she will be taking it to Jim Crowley’s laboratory at Boise State University for a Thermal Ionization Mass Spectrometry (TIMS) derived date (funding for this has already been generated). As a more positive and cost efficient age-dating ( and provenencing) method we propose to collect a series of 10 suites of detrital zircons from fine- to medium-grained sandstone beds sampled from the base of the Palingkloof member through to the upper Katberg Formation at 3 widely- separated and biostratigraphically well-defined EPME sections. Trials have already been conducted with Triassic detrital zircon samples from the Karoo which yielded numerous Permian age populations that suggest extensive volcanism during the P-Tr transition (Huttenlocker pers. comm., 2021), thus adding to the potential value of this methodology for this project. The detrital zircon populations will be sent for Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) analyses at the Central Analytical Facility (CAF, Stellenbosch University). We intend to extract enough young zircons to yield credible maximum depositional ages and also demonstrate a younging-upwards sequence at each site. Similar detrital zircon sampling has been successful in the South American Magallanes (Jurassic/Cretaceous) basin where Bayesian statistical methods have been applied to interpolate the time intervals between samples and derive depositional rates for the succession (Johnstone et al., 2019). If the sequence of detrital dates from the Karoo sections is good, and funds are available, the best-looking zircons from the youngest populations would then be sent to Boise State University (US) for more precise TIMS dating. In addition, our geochronological analysis will provide anchor points to which a carbon isotope stratigraphy can be calibrated, helping to further resolve the position of the EPME/PTB. We will sample pedogenic carbonate nodules through the entire LAZ on one of our new PTB sections ( +/-30 samples). These will be analysed (likely at CAF, Stellenbosch) for stable carbon and oxygen isotope ratios as a chemical signature of the global ecosystem collapse at the PTB. This chemo-stratigraphic methodology has gained popularity among the PTB workers worldwide. Two Karoo PTB sections already have good isotope records and we would like to add at least one more with this project proposal. It is predicted that the results will reflect the global negative “spike” in stable carbon isotope ratios that are closely correlated with the extinction event in the marine realm. If so, the stratigraphic positioning of this spike will indicate 252 My time-equivalent beds in our new PTB sections.