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Molecular, micro- and ultrastructural investigations of labile tissues in deep time

Gren, Johan LU (2017)
Abstract (Swedish)
Denna avhandling behandlar en mängd mikrostrukturella och molekylära lämningar som påträffats i ett antal fossil. Resultaten presenteras i sex vetenskapliga artiklar med det gemensamma syftet att grundligt studera dessa lämningar med hjälp av såväl nya som vedertagna analysmetoder. Avhandlingens huvudsakliga frågeställningar är dels vad denna typ av fossila spår kan säga om de studerade djurens biologi, ekologi och beteende, samt vilka analysmetoder som är bäst lämpade för att kunna utröna detta.

Avhandlingen baseras på en serie fallstudier där jag undersökt fossil från ett flertal olika djurgrupper från olika geologiska tidsåldrar. Fossilen är insamlade från ett antal geologiska lokaler runtom i världen. Bland de metoder som... (More)
Denna avhandling behandlar en mängd mikrostrukturella och molekylära lämningar som påträffats i ett antal fossil. Resultaten presenteras i sex vetenskapliga artiklar med det gemensamma syftet att grundligt studera dessa lämningar med hjälp av såväl nya som vedertagna analysmetoder. Avhandlingens huvudsakliga frågeställningar är dels vad denna typ av fossila spår kan säga om de studerade djurens biologi, ekologi och beteende, samt vilka analysmetoder som är bäst lämpade för att kunna utröna detta.

Avhandlingen baseras på en serie fallstudier där jag undersökt fossil från ett flertal olika djurgrupper från olika geologiska tidsåldrar. Fossilen är insamlade från ett antal geologiska lokaler runtom i världen. Bland de metoder som använts kan nämnas ljus- och elektronmikroskopi, datortomografi och molekylära analyser. De senare innefattar bland annat s.k. ToF-SIMS (en mycket känslig
spektrometrimetod för att studera ytstrukturer), infraröd mikrospektroskopi och röntgenabsorptionsspektroskopi.

Bland resulten finner vi att man genom mikroskopi och histologisk analys av tänder från bland annat mosasaurier (jättelika, numera utdöda marina reptiler) kan beräkna dentinets (tandvävnadens) bildningshastighet. Eftersom dentinbildningen ligger till grund för tändernas tillväxthastighet kan man dra slutsatser om djurens tandersättningscykler (i likhet med nu levande reptiler bytte dessa djur regelbundet sina tänder). Jag påvisar också att tänderna hos större mosasauriearter tog längre tid att nå full storlek än tänderna hos mindre arter. Dock skedde dentinbildningen med högre hastighet i de större tänderna,
vilket innebar att djuren snabbare kunde ersätta förlorade tänder.

Genom studier av ögon, hud och fjädrar från en mängd fossil observerade jag ansamlingar av mikrometerstora, runda till avlånga kroppar i den bevarade vävnaden. Liknande mikrostrukturer har tidigare, vid olika tillfällen, beskrivits som så kallade melanosomer (dvs. pigmentbärande cellorganeller) och som fossiliserade bakterier. För att kunna säkerställa mikrokropparnas härkomst utförde jag och mina medförfattare molekylära och ultrastrukturella analyser av de fossila bildningarna och jämförde sedan resultaten med motsvarande analyser av modernt melanin och andra liknande kemiska föreningar. Resultaten
visar mycket riktigt att molekylära rester av eumelanin återfinns i nära anslutning till de observerade mikrostrukturerna, vilket tydligt talar för att de är melanosomer.

Utöver de studier som redovisas i de bifogade vetenskapliga artiklarna så inkluderar avhandlingen även en kort redogörelse för hur melanin uppträder i ögon, hud och fjädrar hos olika ryggradsdjur, samt dess förekomst i vissa svampar och bakterier. En översikt över de olika metoder som tillämpats i projekten presenteras, och följs av en diskussion om de möjliga slutsatser som kan dras och de svårigheter som bör beaktas inom denna typ av paleontologi.

Bevarade melanosomer kan potentiellt bidra med information rörande ett flertal biologiska och ekologiska företeelser som inte tidigare kunnat beaktas hos förhistoriskt liv. Det råder dock ännu ingen konsensus kring hur vi enklast kan säkerställa dessa “melanosomliknande” mikrostrukturers ursprung. Jag anser därför att en grundlig undersökning av sådana fossila rester, inklusive kemiska
analyser, bör tillämpas för varje enskild studie – åtminstone tills vi uppnått enighet kring vilka kriterier som måste uppfyllas för att mikrofossilen ska kunna identifieras med säkerhet. (Less)
Abstract
This thesis comprises investigations of microstructures and molecular remains, preserved in a variety of fossil specimens. The results are presented in six papers, collectively aiming to thoroughly examine fossil traces of such remains by employing a combination of both established and relatively new analytical methods. The main questions asked are: What can we learn about the biology, ecology and behaviour of ancient organisms by studying these fossilised remnants, and what methods are best suited to accomplish this?
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... (More)
This thesis comprises investigations of microstructures and molecular remains, preserved in a variety of fossil specimens. The results are presented in six papers, collectively aiming to thoroughly examine fossil traces of such remains by employing a combination of both established and relatively new analytical methods. The main questions asked are: What can we learn about the biology, ecology and behaviour of ancient organisms by studying these fossilised remnants, and what methods are best suited to accomplish this?
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. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Dr. McNamara, Maria, School of Biological, Earth and Environmental Sciences, University College Cork, Ireland
organization
publishing date
type
Thesis
publication status
published
subject
keywords
eumelanin, fossils, histology, integument, IR microspectroscopy, melanin, melanosomes, molecular palaeontology, ToF-SIMS, XAS
pages
105 pages
publisher
Lund University, Faculty of Science, Department of Geology, Lithosphere and Biosphere Science
defense location
Lecture hall “Pangea”, Geocentrum II, Sölvegatan 12, Lund
defense date
2018-01-19 13:15
ISBN
978-91-87847-35-6
978-91-87847-34-9
language
English
LU publication?
yes
id
b393d839-0ea8-4bb1-bbe3-e069c342d51a
date added to LUP
2017-12-07 11:06:06
date last changed
2018-01-03 12:27:04
@phdthesis{b393d839-0ea8-4bb1-bbe3-e069c342d51a,
  abstract     = {This thesis comprises investigations of microstructures and molecular remains, preserved in a variety of fossil specimens. The results are presented in six papers, collectively aiming to thoroughly examine fossil traces of such remains by employing a combination of both established and relatively new analytical methods. The main questions asked are: What can we learn about the biology, ecology and behaviour of ancient organisms by studying these fossilised remnants, and what methods are best suited to accomplish this?<br/>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. <br/>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.<br/>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.<br/>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.},
  author       = {Gren, Johan},
  isbn         = {978-91-87847-35-6},
  keyword      = {eumelanin,fossils,histology,integument,IR microspectroscopy,melanin,melanosomes,molecular palaeontology,ToF-SIMS,XAS},
  language     = {eng},
  pages        = {105},
  publisher    = {Lund University, Faculty of Science, Department of Geology, Lithosphere and Biosphere Science},
  school       = {Lund University},
  title        = {Molecular, micro- and ultrastructural investigations of labile tissues in deep time},
  year         = {2017},
}