Discovering Hominins - Application of Medical Computed Tomography (CT) to Fossil-Bearing Rocks from the Site of Malapa, South Africa

Abstract

In the South African context, computed tomography (CT) has been used applied to individually prepared fossils and small rocks containing fossils, but has not been utilized on large breccia blocks as a means of discovering fossils, and particularly fossil hominins. Previous attempts at CT imaging of rocks from other South African sites for this purpose yielded disappointing results. For this study, 109 fossil- bearing rocks from the site of Malapa, South Africa were scanned with medical CT prior to manual preparation. The resultant images were assessed for accuracy of fossil identification and characterization against the standard of manual preparation. The accurate identification of fossils, including those of early hominins, that were not visible on the surface of individual blocks, is shown to be possible. The discovery of unexpected fossils is reduced, thus lowering the potential that fossils could be damaged through accidental encounter during routine preparation, or even entirely missed. This study should significantly change the way fossil discovery, recovery and preparation is done in the South African context and has potential for application in other palaeontological situations. Medical CT imaging is shown to be reliable, readily available, cost effective and accurate in finding fossils within matrix conglomerates. Improvements in CT equipment and in CT image quality are such that medical CT is now a viable imaging modality for this palaeontological application.

Finding fossils in Malapa breccia – medical CT scanning or micro-CT scanning?

“…Reference was also made to prior work done with low energy scanning. 11 Micro-CT images were reconstructed with micro-CT Pro v2.2 associated with the Nikon Metrology XTH 225/320 LC dual source industrial CT system. Three objects, thought to represent potential fossils, were chosen from within each block for evaluation.…”

“…Mass use of XCT to image Malapa breccia has been undertaken and the predicted findings from imaging have been compared to the actual post-preparation findings. 11 Smilg and Berger 11 demonstrated good correlation and suggested that XCT is a valuable imaging modality in the triage process. There is considerable advantage to being able to know the contents of a rock ahead of costly, time-consuming 'blind' manual preparation.…”

Taphonomic Analyses of Cave Breccia in Southeast Asia: A Review and Future Directions

“…The extraction of incorporated aggregates from breccia samples is particularly destructive (Dominguez-Bella et al, 2012). The properties that make excavation difficult are the very properties that resist forces eroding unconsolidated cave deposits, preventing the removal or destruction of incorporated fossils (Pickle, 1985;Smilg & Berger, 2015). The hardness and density of breccia creates resistance to the natural erosive forces produced when a large volume of low-velocity water is trapped within a considerable area of the cave cross-section (Pickle, 1985).…”

Hidden treasures uncovered: successful detection of fossils below the surface in large limestone blocks using a standard medical X-ray CT scanner

“…X-ray technology in palaeontology has been used ever since, and has been recognized as being invaluable, as exemplified by the important and aesthetically superb work of Hohenstein (Hohenstein 2004). The use of X-ray CT scans in palaeontology was also attempted relatively soon (Jungers andMinns 1979, Conroy andVannier 1984) after the technique was made available (Hounsfield 1973) and is now the most commonly applied approach for digitalisation of fossil specimens (e.g., Tafforeau et al 2006, Cunningham et al 2014, Sutton et al 2014, Schilling et al 2014, Smilg and Berger 2015, Lautenschlager 2016, Rowe et al 2016, Racicot 2017.…”