An Analysis of Enthesis-Bone Microstructure: Implications for Paleontological Soft Tissue Reconstructions.
Date
2021-08
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Abstract
In the absence of direct preservation, evaluating a fossil organism’s soft tissue anatomy can be a daunting task. Studies that aim to evaluate fossil soft tissues must often rely on clear soft tissue bony correlates, such as bony eminences or concavities in the bone surface. These eminences and concavities are formed at the site of soft tissue attachment to bone, called entheses. However, even in large-bodied, adult organisms, a considerable proportion of soft tissues do not leave these clear indicators. Therefore, the evaluation of bony eminences/concavities is coupled with the use of an extant phylogenetic bracket. However, some fossil taxa are so phylogenetically removed from their extant bracketing taxa that anatomical comparisons are dubious at best. I have shown that scanning electron microscopy and histological staining make it possible to identify areas of soft tissue attachment on the bone surface in the absence of macroscopically visible eminences or concavities. There is also a differentiation between tissue types (muscle, tendon, articular cartilage, and aponeurosis) with collagen fibres incorporated into the bone tissue. At areas of articular cartilages, the surface is relatively smooth but with small, organized hummocky structures. Areas of fleshy muscle attachment are generally planar but with occasional round projections where the collagen fibres have been incorporated into bone tissue. Tendon entheses are areas where long string-like collagen fibres have been incorporated into bone tissue, usually within concave impressions on the bone surface. These areas are generally more organized than other entheses. Lastly, aponeurotic entheses are large areas of thick, high-density, disorganized collagen fibres. All four categories of bone surface microstructure have been observed through broad taxonomic sampling using extant organisms, and the same morphologies are also seen in three-dimensional preserved fossil specimens. These four bone surface microstructures are successfully categorized using image classification programming with novel convolutional neural network architecture. Using polarimetry, I quantify the differences between bone surface microstructures by measuring the orientation of collagen fibres and the homogeneity of collagen fibre density throughout the enthesis bone’s thickness.
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Keywords
Enthesis, Vertebrate Anatomy, Muscle Reconstruction, Vertebrate Paleontology
Citation
Whitebone, S. A. (2021). An analysis of enthesis-bone microstructure: implications for paleontological soft tissue reconstructions (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.