Pigmented and Organically-Preserved Soft-Bodied Fossils: Using Taphonomic Mode to Interpret Anatomy

Melanin is a ubiquitous pigment found throughout a variety of vertebrate tissues where it fulfils several important roles including colour patterning, ultraviolet protection, and transmission of nerve impulses. It is synthesised in a membrane-bound organelle termed a melanosome, the geometry of which can aid in determining the function of various pigmented tissues. Melanin and melanosomes are extremely recalcitrant and are known to fossilise and palaeontologists have used the presence of melanin and the geometry of melanosomes to address numerous evolutionary questions, from reconstructing the plumage colours of feathered dinosaurs, to the development of a sophisticated camera-style eye in lamprey. Whilst melanin and melanosomes have been shown to remain relatively unaltered during diagenesis, what is not yet fully understood is whether post-mortem processes such as decay alter the geometry of melanosomes or affect the distribution of melanin within the pigmented anatomy of phylogenetically significant organisms. To address these uncertainties, this thesis presents the results of four comprehensive taphonomic experiments investigating the pigmented anatomy of aquatic vertebrates, three of which investigate melanosome geometry and melanin distribution during decay in extant and fossil lamprey alongside distinctly patterned teleost fish, and one investigates the pigmented anatomy of a lamprey-like Devonian fossil Euphanerops longaevus. It was shown that melanosomes from different lamprey tissues retained their geometry throughout decay, with eye melanosomes providing the only exception, changing their geometry from sub-spherical to more elongate forms. Crucially, these changes were not sufficient to alter any interpretations of function based on their shape. Melanosome geometry was also investigated using Procrustes superimposed semi-landmark coordinates in the hope of providing more subtle shape information. However, our results demonstrate that using aspect ratios is sufficient to capture the extent of melanosome geometries. Melanin distribution was found to change during decay, either aggregating into globules or dispersing into surrounding tissues. This alteration can lead to the appearance of new skin pigment patterns. Anatomical features in Euphanerops preserve melanosomes and melanin, extending the fossil record of this pigment by 70 Ma.