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Vertebrate Synchrotron projects

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ProposalDescription: 

This loan seeks to obtain high-resolution CT data from a variety of vertebrate specimens in care of the Wits-ESI to support student led research projects. The first project, which will collect data for the PhD of Bailey Weiss (Wits ESI), seeks to non-destructively scan the limbs of a variety of early branching crocodylomorphs for palaeohistological reconstruction. These specimens represent either the best or the only postcranial material for their respective species, and by scanning them at high resolution we hope to obtain data suitable for reconstructing their growth history, and data suitable for imaging their ankle morphology. Growth history is poorly understood in extinct crocodylomorphs, and while living crocodiles have slow metabolic rates and slow growth, their common archosaurian ancestors had much more rapid growth and potentially higher metabolic rates. Understanding when the crocodylomorph line changed its growth patterns is therefore of macroevolutionary importance. Surprisingly, the earliest crocodylomorphs show evidence of having highly active, terrestrial lifestyles, with erect postures and running capability that is lacking in living members of the group. Our scans of the ankle of Orthosuchus in particular will be useful for understanding the mechanics of these postures because of the intrinsic role the ankle plays in terrestrial locomotion. These data are tightly linked to the understanding of growth and metabolism from the first objective, and we hope that by integrating locomotory data with growth history data, we can gain a better picture of what the life habits of the earliest crocodylomorphs were. The resolution necessary for palaeohistology (±.7 micron voxel size) precludes scanning at any facility in South Africa. The second project seeks to image the skull of BP/1/8468, a potentially new sauropodomorph taxon from the lower Elliot Fomation. This skull has been scanned at the Wits Microfocus CT lab, but we were unable to penetrate the extremely dense matrix. These scans will be reconstructed to image each bone in three dimensions and to compare the anatomy to other, better-known Elliot sauropodomorph, especially Massospondylus carinatus.

Expanded_Motivation: 

Methodology (short): We will image the fossil samples using a multiresolution approach to achieve high resolution scans (voxel size < 0.7µm) of areas of interest using the BM05 beamline of the ESRF and its associated instrumentation. For histological scans, a series of rapid low resolution scans will be done first (binning 2x2) to locate an ROI before starting a higher resolution acquisition. The final microtomography data will be visualized in VG Studio Max 3.4.0 using an averaging of several successive slices to develop a projection and optical imaging through cross polarized filters to observe structures of interest [6]. For anatomical scans, we will achieve isotropic voxel sizes of between 22 and 100 microns (depending on fossil size). We will obtain clear images with long propagation phase contrast and a high energy monochromatic beam to obtain enough transmission through the blocks and avoid beam hardening. Due to the size of the blocks, we will use the large beam BM18 if possible associated to the maximum energy available (180 keV) as well as the longest propagation distance (~11 m) to maximize phase contrast. The resulting data will be reconstructed by Kathleen Dollman at the ESRF using proprietary scripts and transmitted to the researchers via a secure FTP site. These data will be then processed at the University of the Witwatersrand VIP facility, and uploaded to secure repositories as warranted. Statement why this study cannot be done in South Africa: These specimens have already been scanned at the Stellenbosch and Wits Microfocus CT laboratories, but these instruments were unable to obtain sufficient resolution to image the fossils within. The ESRF has dedicated palaeontological beam lines that are capable of producing scans of these objects at resolutions suitable for anatomical and histological reconstructions. There is no comparable synchrotron facility in all of Africa. The long-standing research agreement between the South African NRF and the ESRF was developed specifically to address this shortcoming and to accommodate research projects of this nature.

ApplicationDate: 

Sunday, June 12, 2022 - 12:53

CaseID: 

18793

OtherReferences: 

ReferenceList: 

Images
BP/1/275a
BP/1/2715c
BP/1/424a
BP/1/4242d
BP/1/4660a
BP/1/4770d
BP/1/5237a
BP/1/5237b
BP/1/8468a
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