The fossil record 2

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

Taphonomy - ‘fossilization’

• The manner and cause of death• Processes of decay and decomposition• Transportation of fossils/potential fossils• Burial of remains• Diagenesis of remains

NB text-book, p. 8-17

• life position, clustering• articulation, breakage,

sorting, orientation• population structure - age

and size frequency• trace fossils • sedimentology

Taphonomic information

• ‘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

1999

Unaltered remains - freezing

Lyuba (age 4 months, 40kya old) - discovered in 2007 in Siberian permafrost

Unaltered remains - freezing

Dima (age 7 months, 40kya old) - discovered in 1977 by gold diggers in a lump of ice near the Kirgilyakh Creek

Unaltered remains - freezing

Unaltered remains - amber

Oligocene (~30Ma) amber, Baltic

Unaltered remains - amber

Oligocene (~30Ma) amber, Baltic

Altered remains - permineralization

Triassic (~230 Ma) trees, Petrified Forest NP, Arizona

Altered remains - recrystallization

NB. mineralogy is unchanged

gastropod/snail

Altered remains - replacement, e.g. aragonite to calcite

Peronoceras fibulatum Placenticeras meeki

calcite aragonite

ammonites

Altered remains - replacement, e.g. aragonite to pyrite

Jurassic (135-205 Ma) ammonites

pyrite

Altered remains - carbonization

fossil fern frond (Neuropteris)

Imprints - moulds and casts

imprints

internal mould

external mould

Chemical/molecular fossils

degree of alteration may be difficult to determine

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.

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)

Chances of fossilization

marine vs. continental environments + scavengers, decomposition

Shrimp - Aeger tipularius

Lagerstätten

Solnhofen (Jurassic, S Germany) - a conservation lagerstätte

deposits of exceptional value- conservation- concentration

Dragonfly - Libellulium

Lagerstätten

Solnhofen (Jurassic, S Germany)

Lagerstätten

Solnhofen (Jurassic, S Germany)

Messel (Eocene, Germany)

Lagerstätten

beetle

Messel (Eocene, Germany)

Lagerstätten

snake

Fish - Cyclurus kehreriMessel (Eocene, Germany)

Lagerstätten

Turtle - Allaeochelys crassesculptataMessel (Eocene, Germany)

Lagerstätten

Mammal - Propalaeotherium parvulum

Messel (Eocene, Germany)

Lagerstätten

Marsupial - Leptictidium nasutum

Messel (Eocene, Germany)

Lagerstätten

Bat - Archaeonycteris trigonodonMessel (Eocene, Germany)

Lagerstätten

Holzmaden (Jurassic, Germany)

Lagerstätten

marine reptile - ichthyosaur

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!!

Stratigraphic bias

Collection bias

e.g. oceans vs. shelf sedimentsEurope vs. Asia, etc.

Quality of the fossil record - biases but ……

Palaeobiology and the Fossil Record Benton & Harper

Quality of the fossil record

Alroy et al. 2008, Science

‘corrected’ for sampling biases

Sepkoski data

PBDB data

Quality of the fossil record