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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 • 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 calcite Peronoceras fibulatum ammonites aragonite Placenticeras meeki Altered remains - replacement, e.g. aragonite to pyrite 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 Mammal - Propalaeotherium parvulum Messel (Eocene, Germany) Lagerstätten Messel (Eocene, Germany) Marsupial - Leptictidium nasutum Lagerstätten Messel (Eocene, Germany) Bat - Archaeonycteris trigonodon Lagerstätten 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
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