Heritage Cases

The exploration and quantitative analyses of inner craniodental features is relevant for assessing the paleobiodiversity and paleobiology of fossil hominins, i.e., how many species co-existed with our ancestors and how did they live and evolve. Recent developments in imaging techniques have been proved to be particularly useful for virtually reconstructing inner craniodental structures. In particular, high-resolution acquisitions may provide crucial information about the inner structure of teeth which might be used for fossil hominin taxonomy (i.e., identifying and classifying fossil specimens), but also hominin brain evolution, as cerebral imprints could be preserved in the inner surface of the cranium, or even the vascular system enclosed by the spongious bone in the cranial vault (e.g., Carlson et al., 2011; Beaudet et al., 2016, 2018). In this context, we are requesting permission to scan the skull of StW 573, the oldest and most complete South African Australopithecus specimen, on I12-JEEP at the Diamond Light Source and on IMAT at the ISIS facilities. Scientific context: The Australopithecus specimen ‘Little Foot’ (StW 573) is the most complete Australopithecus ever found in the history of paleoanthropology. Besides its exceptional degree of preservation and completeness, the ‘Little Foot’ skeleton is remarkable for its geological age of 3.67 million years. Accordingly, this unique specimen currently represents the oldest example of Australopithecus in the southern African fossil record. The exploration and quantitative analyses of inner craniodental features is relevant for assessing the paleobiodiversity and paleobiology of fossil hominins, i.e., how many species co-existed with our ancestors and how did they live and evolve. More specifically, X-rays microtomograhy, including synchrotron radiation, as well as neutron-based imaging techniques, may provide crucial information about the inner structure of teeth which might be used for fossil hominin taxonomy (i.e., identifying and classifying fossil specimens), but also hominin brain evolution, as cerebral imprints could be preserved in the inner surface of the cranium, or even the vascular system enclosed by the spongious bone in the cranial vault (e.g., Carlson et al., 2011; Beaudet et al., 2016, 2018). In this context, we are developing a project for scanning the skull of ‘Little Foot’ to provide critical evidence for the reconstruction of early hominin paleobiology in South Africa. We previously successfully quantified variation in the enamel-dentine junction shape, endocranial organization and cranial vault composition in fossil and extant primates based on imaging techniques (Beaudet et al, 2016, 2018). Moreover, we applied neutron-based imaging techniques for the first time in fossil primate records (Beaudet et al., 2016). Accordingly, we are familiar with both X-rays and neutron-based imaging techniques and with data analysis using microtromographic resources. Experiment proposed: Since we are interested in inner craniodental structures, the skull should be scanned at a very fine spatial resolution (<50 microns) with a good contrast between the tissues (e.g., enamel and dentine, cortical and spongious bones) and between the tissues and the sediments (e.g., cranium filled in with sediments). Unfortunately, classical microtomographic radiation at the home institution (i.e., Evolutionary Studies Institute, University of the Witwatersrand, South Africa) failed to reveal these very fine details. In addition to the synchrotron scanning, which will provide very high spatial resolution on very small priority areas of the cranium, we aim to employ neutron scanning. Because of the unique ability of neutrons to penetrate materials opaque to X-rays and by being more strongly attenuated by the organic material, the interaction mechanism of neutrons with matter differs from X-rays. Accordingly, we suggest combining the synchrotron-based analysis with neutron-based imaging techniques. Neutron scanning is also a non-destructive imaging technique (Kardjilov et al., 2011). Since neutron radiography and neutron microtomography are bound to deliver contrast very different from X-rays, the two analyses could be successfully combined for investigating biological organisms and structures (e.g. Sutton, 2008). This combination of techniques has been applied previously to fossils with great success (e.g. Jones et al., 2018). On IMAT, we will aim for 200 microns resolutions with 3000 projections. As we would likely need to test some parameters for getting the best resolution and contrast possible, we would request 4 days of beam time at the synchrotron facility and 2 days of beam time at the neutron facility. We have been working very closely with Dr Winfried Kockelmann, chief beamline scientist at the neutron facility on all protocols for the neutron scanning. Dr Kockelmann has offered to be contacted about any specific questions about the scanning and has been working with the synchrotron beamline scientists to develop the most efficient and cohesive protocol to answer our questions while limiting the irradiation of the specimen as much as possible. Estimates have been calculated based on the weight and chemical composition of the specimen. XRF analysis of breccia samples of the same deposit as the specimen provided the calibration for the estimates that identify particularly active chemical compounds. Based on all the information, the residual radiation of the fossil would drop below 0.01 µSv/h (micro Sieverts) after a few hours. To put this in perspective, background radiation in London is 0.25 µSv and background radiation on a flight at 12,000m altitude is 5 µSv/h. A 1 hour passenger flight generally provides a radiation dose of 3 µSv. 0.01 µSv/h is well within the personal safety threshold considered by the 10 CRF Part 20 – Standards for Protection Against Radiation, published by the US Nuclear Regulatory Commission which cites 1 µSv and a dose of less than 0.5 µSv/h, but still too high for the health and safety limits on at the neutron facility and so the specimen will need to remain in the onsite safe room for another 5 to 14 days. Estimates of deactivation time will be calculated more accurately one the initial preparation scan. At which point, we will better understand the capacity of the neutron facility to answer our research questions and we can assess how to proceed with the scanning. There is no scientific evidence of physical damaged being caused by neutron scanning although a temporary slight discolouration of fossil surfaces has been reported immediately after the scanning – a change that reverses quickly. Due to the expense and risk of transporting and storing this exceptional specimen, it would be necessary to ensure that the X-ray and Neutron studies are carried out around the same time, taking advantage of the proximity of Diamond and ISIS. Neutron scanning is now scheduled for 5-9 July. Results expected Our exploration of the inner craniodental features preserved in the skull of StW 573 will be critical for discussing (i) the morphology of the enamel-dentine junction and its implication in terms of diagnostic traits, (ii) brain circumvolutions and the evolution of the brain in early hominins and (iii) diploic vessels in the cranial vault and potential correlation with brain thermoregulation. Additionally, for the first time, a fossil hominin skull would be scanned by combining both synchrotron and neutron imaging techniques and this study could be used in the future as a reference for subsequent paleoanthropological analyses. Results provided within the frame of this project will be presented both at local scientific meetings (e.g., Palaeontological Society of Southern Africa) and international conferences (e.g., Paleoanthropology Society, American Association of Physical Anthropologists, European Society for the study of Human Evolution) and submitted to an accredited journal (ISI) for publication. Additionally, this initial project might be an opportunity to initiate a fruitful collaboration between the Diamond Light Source and the University of the Witwatersrand. Safety and security protcols for transport include: Three scientists accompanying the skull personally to the Diamond Light Source facility; business class transport for Professor Clarke, who will carry the specimen in a dedicated, custom and locked pelican case; Private, secure transport between the airport and facility both directions, with dedicated professional driver; secure safe room at Diamond Light Source for sensitive fossils in which the skull will be kept at all times when not being scanned; special insurance covered by Wits University for the transport of the skull.