the fossil record 2. what is a fossil? where do we find fossils? why study fossils? –palaeobiology...
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The fossil record 2
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The fossil record 2
• What is a fossil?• Where do we find fossils?• Why study fossils?
– Palaeobiology– Geochronology– Palaeoenvironments/climates
• How are fossils formed?• Types of fossil preservation• Quality of the fossil record
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Taphonomy - ‘fossilization’
• The manner and cause of death• Processes of decay and decomposition• Transportation of fossils/potential fossils• Burial of remains• Diagenesis of remains
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NB text-book, p. 8-17
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• life position, clustering• articulation, breakage,
sorting, orientation• population structure - age
and size frequency• trace fossils • sedimentology
Taphonomic information
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• ‘Unaltered’ remains• Soft parts - very rare
– Freezing– Mummification– amber, etc.
• Hard parts
• Altered remains– Petrifaction
• Permineralization• Recrystallization• Replacement
– Carbonization
• Imprints– Moulds/casts– impressions
• Tracks, trails and burrows
Types of preservation
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1999
Unaltered remains - freezing
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Lyuba (age 4 months, 40kya old) - discovered in 2007 in Siberian permafrost
Unaltered remains - freezing
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Dima (age 7 months, 40kya old) - discovered in 1977 by gold diggers in a lump of ice near the Kirgilyakh Creek
Unaltered remains - freezing
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Unaltered remains - amber
Oligocene (~30Ma) amber, Baltic
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Unaltered remains - amber
Oligocene (~30Ma) amber, Baltic
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Altered remains - permineralization
Triassic (~230 Ma) trees, Petrified Forest NP, Arizona
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Altered remains - recrystallization
NB. mineralogy is unchanged
gastropod/snail
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Altered remains - replacement, e.g. aragonite to calcite
Peronoceras fibulatum Placenticeras meeki
calcite aragonite
ammonites
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Altered remains - replacement, e.g. aragonite to pyrite
Jurassic (135-205 Ma) ammonites
pyrite
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Altered remains - carbonization
fossil fern frond (Neuropteris)
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Imprints - moulds and casts
imprints
internal mould
external mould
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Chemical/molecular fossils
degree of alteration may be difficult to determine
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Quality of the fossil record• Chances of fossilization
– Soft parts vs. hard parts
• Lagerstätten• Biases
– Sedimentary environment• e.g. marine vs. continental
– Stratigraphic bias• older rocks - less exposure, tectonized
– Collection• bias towards commonest and most
accessible sedimentary facies (~environments)
• NB. oldest ocean crust 165 m.y.
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Discalioides jellyfish, Oligocene, Provence, Southern France
Chances of fossilization
~60% of marine animals are soft bodied and usually unrepresented in the fossil record (NB shell and coral carbonate is also broken down by bioerosions - up to 60% in coral reef settings)
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Chances of fossilization
marine vs. continental environments + scavengers, decomposition
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Shrimp - Aeger tipularius
Lagerstätten
Solnhofen (Jurassic, S Germany) - a conservation lagerstätte
deposits of exceptional value- conservation- concentration
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Dragonfly - Libellulium
Lagerstätten
Solnhofen (Jurassic, S Germany)
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Lagerstätten
Solnhofen (Jurassic, S Germany)
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Messel (Eocene, Germany)
Lagerstätten
beetle
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Messel (Eocene, Germany)
Lagerstätten
snake
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Fish - Cyclurus kehreriMessel (Eocene, Germany)
Lagerstätten
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Turtle - Allaeochelys crassesculptataMessel (Eocene, Germany)
Lagerstätten
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Mammal - Propalaeotherium parvulum
Messel (Eocene, Germany)
Lagerstätten
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Marsupial - Leptictidium nasutum
Messel (Eocene, Germany)
Lagerstätten
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Bat - Archaeonycteris trigonodonMessel (Eocene, Germany)
Lagerstätten
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Holzmaden (Jurassic, Germany)
Lagerstätten
marine reptile - ichthyosaur
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Quality of the fossil record
• Chances of fossilization– Soft parts vs. hard parts
• Lagerstätten• Biases
– Sedimentary environment• e.g. marine vs. continental
– Stratigraphic bias• older rocks - less exposure, tectonized
– Collection• bias towards commonest and most
accessible sedimentary facies
• oldest ocean crust 165 m.y.
UP TO HERE!!
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Stratigraphic bias
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Collection bias
e.g. oceans vs. shelf sedimentsEurope vs. Asia, etc.
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Quality of the fossil record - biases but ……
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Palaeobiology and the Fossil Record Benton & Harper
Quality of the fossil record
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Alroy et al. 2008, Science
‘corrected’ for sampling biases
Sepkoski data
PBDB data
Quality of the fossil record