DNH Synchrotron_2024

Aim/rationale:

Approximately 2 million years ago in South Africa, the hominin family tree experienced an explosion of diversity (Herries et al., 2020). The shift from a single early human species dominating the landscape to three unique genera coincides with a climactic change likely bringing new evolutionary pressures and opportunities. It is at this point that we see the earliest member of our own lineage, Homo erectus, emerge. Our earliest ancestor would have had to co-exist with two other hominin genera, Australopithecus and Paranthropus. The way in which these three groups adapted to pressures and developed separate niches dictated the way we evolved and caused both Paranthropus and Australopithecus to, eventually, go extinct. Joannes-Boyau et al., (2019) conducted trace element and stable isotope analysis of A. africanus specimens from an earlier time period sampled from the site of Sterkfontein. It was found that this species may have been practicing cyclical weaning – the resurgence of breastfeeding behaviours later into childhood as an adaptation to food instability. It is also known that Paranthropus robustus from the neighbouring site of Swartkrans shows a significantly higher degree of variability in their diet as compared to the eastern African Paranthropus boisei based on C3/C4 ratios (Sponheimer et al., 2006). However, neither of these species were likely to have existed at the start of species diversity in South Africa or during the drastic climactic changes resulting in said diversity. Trace element and stable isotope sampling of material from the nearby Drimolen Main Quarry (DMQ) fossil site has allowed for an assessment of the feeding and migratory behaviours of the basal-most representation of Paranthropus (Martin and Leece et al., 2021) and the earliest H. erectus (Herries et al., 2020). Further, DMQ overlaps with the latest occurring Australopithecus species in South Africa, A. sediba at ~1.95 Ma (Berger et al., 2010; Dirks et al., 2010) making a comparison to cyclical breastfeeding identified by Joannes-Boyau et al. (2019) crucial. The sampling of the Drimolen (DMQ) material is complete and has yielded promising results. Elemental maps provide insight into diffusion and adsorption patterns of each element, and help account for diagenetic processes using rare earth elements (e.g. Ce or Eu). Barium (Ba) and strontium (Sr) maps describe hominins’ dietary pattern, the trophic level of the species and reconstruct the nursing sequence of each specimen (Joannes-Boyau et al., 2019). Finally, maps of calcium and strontium isotope ratios were obtained on the Multicollector ICPMS, allowing us to better understand the migration pattern, and vector of mobility of each individual. To firmly establish our findings within the developmental timeline, it becomes imperative to factor in information regarding the enamel's birth line and the specific growth rate, as these are essential elements in unravelling the early-life exposome of the individuals under investigation.As shown by Joannes-Boyau et al., (2019), these analyses can provide useful information in isolation. However, coupling these results with markers of growth will allow for a more fine-grained interpretation of the early life of these human ancestors. The beginning of extended childhood – a specialised adaption that make us (H. sapiens) unique as a species– has long been questioned. Being able to examine aspects such as the exact age of the transition to solid foods, age of migrations, the presence or absence of seasonal dietary behaviours, etc., would provide an insight into our evolutionary history that had previously been considered unobtainable.

The enamel of teeth in humans and our relatives grows incrementally, with around 4 microns added every day (Lacruz and Bromage, 2006; Smith et al., 2015). These daily striations then form long-line periodicity bands that can be related to elemental and isotopic data collected for this project (Bromage, 2005; Joannes-Boyau et al., 2019). Daily incremental growth striae must be captured to determine the age of isotopic or elemental markers (and thus dietary or migratory behaviours). Historically, incremental growth data has been collected primarily through the creation of thin sections and the employment of confocal imagery (i.e. Bromage 2005). This method, however, is now excluded under South African Heritage Resource Agency (SAHRA) and UNESCO permitting guidelines, as it results in significant destruction of precious fossil resources. Scans collected using the Max Plank portable microCT, the NECSA XTH 25 ST, and the University of the Witwatersrand XTH 225/320 LC micro-CT were not able to image incremental growth lines necessary for this study. However, international synchrotrons have been used in the past to collect incremental growth information from hominin teeth and so this methodology is proven to work (i.e. Smith et al., 2015).

REFERENCES
Berger, L. R., De Ruiter, D. J., Churchill, S. E., Schmid, P., Carlson, K. J., Dirks, P. H., & Kibii, J. M. (2010). Australopithecus sediba: a new species of Homo-like australopith from South Africa. science, 328(5975), 195-204.

Bromage, T. G., Perez-Ochoa, A., & Boyde, A. (2005). Portable confocal microscope reveals fossil hominid microstructure. Microscopy and Analysis, 19(3), 21-23.

Herries, A.I.R., Martin, J.M., Leece, A.B., Adams, J.W., Boschian, G., Joannes-Boyau, R., Edwards, T.R., Mallett, T., Massey, J., Mursewski, A., Neubauer, S., Pickering, R., Strait, D.S., Armstrong, B.J., Baker, S., Caruana, M.V., Denham, T., Hellstrom, J., Moggi-cecchi, J., Mokobane, S., Penzo-Kajewski, P., Rovinsky, D.S., Schwartz, G.T., Stammers, R.C., Wilson, C., Woodhead, J., Menter, C. 2020. Contemporaneity of Australopithecus, Paranthropus, and early Homo erectus in South Africa. Science. eaaw7293 1-19.

Joannes-Boyau, R., Adams, J.W., Austin, C., Arora, M., Moffat, I., Herries, A.I.R., Tonge, M.P., Benazzi, S., Evans, A.R., Kullmer, O., Wroe, S., Dosseto, A., Fiorenza, L. 2019. Elemental signatures of Australopithecus africanus teeth reveal seasonal dietary stress. Nature. 572, 112-115

Martin JM, Leece AB, Neubauer S, Baker SE, Mongle CS, Boschian G, Schwartz GT, Smith AL, Ledogar JA, Strait DS & Herries AIR. 2021. Drimolen cranium DNH 155 documents microevolution in an early hominin species. Nat. Ecol. Evol., 5(1), pp.38-45.

Smith, T. M., Tafforeau, P., Le Cabec, A., Bonnin, A., Houssaye, A., Pouech, J., ... & Menter, C. G. (2015). Dental ontogeny in Pliocene and early Pleistocene hominins. PloS one, 10(2), e0118118.