Restriction lift date: 2023-08-31
The taphonomy of vertebrate melanosomes
Loading...
Files
Date
2020-08-31
Authors
Rossi, Valentina
Journal Title
Journal ISSN
Volume Title
Publisher
University College Cork
Published Version
Abstract
The field of fossil colour is emerging rapidly as a new focus of palaeobiological research. Evidence of melanosomes, micron-sized organelles containing melanin, found in skin, feathers and hair of exceptionally preserved fossil vertebrates has been used to infer melanin-based integumentary colouration of extinct animals. Although melanosomes from the integument are well studied, less attention has been given to melanosomes from non-integumentary tissues; the impact of non-integumentary melanosomes on inferences of fossil colour is unknown. The correct identification of integumentary melanosomes requires a mechanism, or multiple mechanisms, to distinguish these from non-integumentary melanosomes. Identification of integumentary melanosomes in fossils is therefore critical to studies of fossil colour. In this thesis the spatial distribution, geometry and chemistry of melanosomes in a taxonomically broad set of extant higher vertebrate tissues were analysed using histology, scanning electron microscopy, synchrotron rapid-scanning X-ray fluorescence and synchrotron X-ray absorption near edge spectroscopy. Data from extant taxa were compared with data from fossil vertebrates from nine Konservat-Lagerstätten. Spatial distribution, geometry and chemistry of fossil melanosomes were analysed using scanning electron microscopy and synchrotron rapid-scanning X-ray fluorescence. Taphonomic experiments simulated the impact of high pressure and temperature and the presence of metal-rich fluids on the morphology and chemistry of melanosomes from the skin and liver of extant amphibians. Histological analysis of tissues in extant taxa shows that internal melanosomes are abundant in all extant taxa and tissues. Moreover, different tissues can be discriminated using melanosome geometry and metal associations. Critically, non-integumentary melanosomes are preserved in fossils and can be identified from the skin using melanosome morphology and chemistry. Nevertheless, in fossils, melanosome geometry and chemistry are altered, and in some case, these indices cannot discriminate between the skin and other organs. Taphonomic experiments show that during maturation, the chemistry of melanosomes from the skin and the liver converges, with melanosomes losing their characteristic tissue-specific chemical signals. This result suggests that the metals-melanin association is unstable during diagenesis.
Collectively, these data provide new fundamental knowledge on the taphonomy of melanosomes, including a new tool for inferring the internal anatomy of fossils using the geometry and chemistry of preserved melanosomes. Moreover, this thesis reveals that, although in some case tissue-specific chemical signals can preserve in fossil melanosomes, the chemistry is unlikely to be fully biological in origin.
Description
Keywords
Fossil colour , Organic chemistry , Synchrotron XRF , Melanosomes , Metals , Experimental taphonomy
Citation
Rossi, V. 2020. The taphonomy of vertebrate melanosomes. PhD Thesis, University College Cork.