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

Taphonomic information life position, clustering articulation, breakage, sorting, orientation population structure - age and size frequency trace fossils sedimentology

Types of preservation ‘Unaltered’ remains Altered remains Imprints 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

Unaltered remains - freezing 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 - 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 ammonites

Altered remains - replacement, e.g. aragonite to pyrite Jurassic (135-205 Ma) ammonites

Altered remains - carbonization fossil fern frond (Neuropteris)

Imprints - moulds and casts internal mould external mould imprints

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.

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) Discalioides jellyfish, Oligocene, Provence, Southern France

Chances of fossilization marine vs. continental environments + scavengers, decomposition

Lagerstätten deposits of exceptional value - conservation - concentration Solnhofen (Jurassic, S Germany) - a conservation lagerstätte Shrimp - Aeger tipularius

Lagerstätten Solnhofen (Jurassic, S Germany) Dragonfly - Libellulium

Lagerstätten Solnhofen (Jurassic, S Germany)

Lagerstätten Messel (Eocene, Germany) beetle

Lagerstätten Messel (Eocene, Germany) snake

Lagerstätten Messel (Eocene, Germany) Fish - Cyclurus kehreri

Lagerstätten Messel (Eocene, Germany) Turtle - Allaeochelys crassesculptata

Lagerstätten Messel (Eocene, Germany) Mammal - Propalaeotherium parvulum Messel (Eocene, Germany)

Lagerstätten Messel (Eocene, Germany) Marsupial - Leptictidium nasutum

Lagerstätten Messel (Eocene, Germany) Bat - Archaeonycteris trigonodon

Lagerstätten Holzmaden (Jurassic, Germany) marine reptile - ichthyosaur Holzmaden (Jurassic, Germany)

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 sediments Europe vs. Asia, etc.

Quality of the fossil record - biases but ……

Quality of the fossil record Palaeobiology and the Fossil Record Benton & Harper

Quality of the fossil record ‘corrected’ for sampling biases Sepkoski data PBDB data Alroy et al. 2008, Science