Mats Eriksson
Professor
Molecular, micro- and ultrastructural investigations of labile tissues in deep time
Author
Summary, in English
The work presented herein has been conducted through a series of case studies performed on fossils representing an array of taxa, collected from different geological ages and settings. Methods applied include light and electron microscopy, computed tomography, and molecular analyses, such as time-of-flight secondary ion mass spectrometry, IR microspectroscopy and X-ray absorption spectroscopy.
Microscopic analysis and histology of teeth from Mesozoic marine reptiles allowed calculations of dentine formation and tooth replacement rates. My findings include evidence that while teeth of larger mosasaur taxa took longer time to develop, their dentine formation rates were more rapid, relative to that of smaller species.
In other fossils, microscopic investigations of eye, skin and feather remnants revealed aggregations of micrometre-sized, sub-rounded to elongate structures. Because similar microbodies have previously been described alternatively as relict melanosomes (i.e. pigment-containing, eukaryotic cellular organelles) and lithified bacteria, my co-authors and I performed chemical and molecular analyses in order to explore the affinity of these structures. To ascertain the chemical identity of our fossil samples, corresponding analyses were carried out also on molecularly similar compounds, including modern eumelanin, as controls. My studies show chemical evidence of animal eumelanin in close association with the microbodies, advocating the melanosome interpretation for the analysed specimens.
Beyond the results reported in the included papers, this thesis provides a short review of melanin formation in vertebrate eyes and integument, as well as in fungi and bacteria which also produce this type of pigment. An overview of the various methods applied is presented and followed by a discussion about possible outcomes and pitfalls when studying fossil microstructures and molecular palaeontology. Whereas remnant melanosomes could potentially provide new insight into a multitude of biological and ecological aspects of ancient life, there is still no straight-forward approach to determine the affinity of ‘melanosome-like’ microstructures found in fossils. Therefore, a thorough investigation of such remains, including chemical analyses, should be applied in each study – at least until a consensus has been reached regarding the minimum amount of criteria to be used for a confident recognition.
Department/s
- Lithosphere and Biosphere Science
Publishing year
2017-12
Language
English
Publication/Series
Litholund theses
Issue
31
Full text
Document type
Dissertation
Publisher
Lund University, Faculty of Science, Department of Geology, Lithosphere and Biosphere Science
Topic
- Geology
Keywords
- eumelanin
- fossils
- histology
- integument
- IR microspectroscopy
- melanin
- melanosomes
- molecular palaeontology
- ToF-SIMS
- XAS
Status
Published
Supervisor
- Johan Lindgren
- Mats Eriksson
ISBN/ISSN/Other
- ISSN: 1651-6648
- ISBN: 978-91-87847-35-6
- ISBN: 978-91-87847-34-9
Defence date
19 January 2018
Defence time
13:15
Defence place
Lecture hall “Pangea”, Geocentrum II, Sölvegatan 12, Lund
Opponent
- Maria McNamara (Dr.)