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2. The discovery of the past

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1 2. The discovery of the past
To study evolution means to dig in the past. The science of past organims is paleontology (greek: palaews: old, logos: science) Paleontology deal with fossils (lat. fodere = to dig) Charles Lyell Georges Cuvier Early paleontology mainly described ancient life within the Linnean framework Modern paleontology tries to reconstruct ancient life. It links therefore ecology and taxonomy. Mary Anning ( ) Richard Owen ( )

2 How do animals fossilize?
Taphonomy (Greek: tafos: burial; nomos: law) Immediate burial Living organism Death Fossil Remains Buried remains Mineralization Decomposition Decay Bleaching Delayed burial Exposed remains Stratinomy Ginkgo biloba Ginkgo adiantoides Much less than 1% of all organisms fossilize Coral fish Coral fish from Jura Bioerosion

3 Fossilized Cyanobacteria (stromatolites) from South Africa
A fossil forest in Dorset, England formed by fossilized bacteria around old tree stumps. Fossilized Cyanobacteria (stromatolites) from South Africa A fossilized dinosaur footprint from New Mexico A mammoth coprolith (fossilized excrements)

4 Immediate and delayed buriages
From B. Ziegler: Allgemeine Paläontologie. Thieme, 1975.

5 What fossilizes? Hard body materials Soft body materials
Substance Examples Calcite (CaCO3) Octocorallia Bryozoa Brachiopoda Polychaeta Ammonita Belemnita Echinodermata Aragonite (CaCO3) Hydrozoa Gastropoda Calciumphosphate Vertebrata (Ca5(OH)(PO4)3) Trilobita Crustacea Opal (SiO2.H2O) Radiolaria Diatomea Porifera Chitin Algae Fungi Arthropoda Cnidaria Priapulida Annelida Cellulose Plantae Tunicata Soft tissues very seldom fossilize Exceptions are Fast drying out in very arid climates Permanent frozen Preservation in amber or asphalt A feathered Dinosaur: Sinosauro-pteryx

6 How complete is the fossil record?
Without hard skeleton Fossils With hard skeleton Fossils Cephalochordata Unknown Vertebrata Often Tunicata Rare Echinodermata Often Chaetognatha Rare Tentaculata Often Pentastomida Unknown Arthropoda Often Tardigrada Unknown Mollusca Often Onychophora Rare Cnidaria Often Pogonophora Unknown Porifera Often Sipunculida Rare Rhizopoda Often Echiurida Unknown Hard skeleton infrequent Nematoda Rare Plathelminthes Unknown Branchiotremata Some taxa often Ctenophora Unknown Annelida Some taxa often Mesozoa Unknown Ciliata Some taxa often Sporozoa Unknown Flagellata Some taxa often

7 Under what conditions do organisms fossilize?
Probability of fossilization Moisture gradient Nutrient rich soils River sediments Anaerobic conditions (moorlands) Volcanic ashes Salinity gradient

8 How complete is the fossil record?
Benton MJ, Willis MJ,  &  Hitchin R Quality of the fossil record through time. Nature 403: Divergence time inferred from cladogram Divergence time inferred from fossils SCI: Quotient of consistent to inconsistent nodes RCI: Relative completeness index GAP: Gap excess index Alba DM, Jordi A, Moya-Sola S Completeness of mammalian fossil record in the Iberian neogene. Palaeobiology 27: 79-83 Neogene Iberian mammals The completeness of the fossil record PT can be calculated from the probability R that a fossil species is preserved at least in one geological layer: Species level: 77% Genus level: 91%

9 The tectonic plates (from David Sanfwell, Scripps Inst. Oceanography)
Continental drift Alfred Lothar Wegener ( ) The tectonic plates (from David Sanfwell, Scripps Inst. Oceanography) Evidence for plate tectonics: Fit of coastlines Distribution of mountains Continuity of fossils Continuity of geological features Isostasy: Earth acts like a fluid From Press et al Understanding earth,

10 Continental drift From C. R. Scotese:

11 How to match phylogeny and plate tectonics

12 Relative dating methods
Fossil dating Relative dating methods Relative dating uses geological strata to infer whether fossils are older or younger than a given stratum Layer 1 Younger Layer 2 Time Layer 2 Older Stratigraphy Morphological primitivism

13 Absolute dating methods
Radiometric dating Most minerals which contain radioactive isotopes are in igneous rocks. The dates they give indicate the time the magma cooled. Potassium 40 is found in: potassium feldspar (orthoclase) muscovite amphibole glauconite Volcanic rocks Sometimes in sediments Uranium may be found in: zircon urananite monazite apatite sphene Carbon 14 is used for bones

14 How to use radiometric dating?
The Rb/Sr System = 1.42 x a-1,  t1/2 = 4.8 x 1010 a b-decay Pt: Amount of daughter atoms through decay Total Decay Original 86Sr is an isotope that is not radioactive not radiogen

15 Recognition of unique events to subdivide time
Radiometric dating Stratigraphy Relative time scale Absolute time scale Geological time scale Recognition of unique events to subdivide time Calibrating geological time Radiomtric dating of layers Raw data Modified from Andy MacRae: Radiometric Dating and the Geological Time Scale.

16 Dendrochronology analyses tree-ring growth patterns.
Fission track Dendrochronology Fission Tracks (FT) are micrometer-sized, linear damage tracks that occur in insulating minerals and that are caused by the spontaneous fission of heavy, unstable nuclides (mostly 238U in natural minerals). Dendrochronology analyses tree-ring growth patterns.

17 History of the earth Steno founded stratigraphy by stating that
geological layers are horizontal and superposed. Deeper layers are older. Nicolas Steno ( ) The Red Rock Canyon, California

18 The geological time scale
Eon Era Period Age at Base (Mya) Duration (Mya) Phanerozoic Cenozoic Quaternary 1.6 Tertiary 65 63.4 Mesozoic Cretaceous 140 75 Jurassic 205 Triassic 250 45 Paleozoic Permian 290 40 Carboniferous 355 Devonian 410 55 Silurian 440 30 Ordovician 510 70 Cambrian 540 Proterozoic Neoproterozoic Ediacaran (Vendian) 630 90 Cryogenian 850 220 Tonian 1000 150 Mesoproterozoic 1600 600 Palaeproterozoic 2500 900 Archean 3800 2950 Hadean 4550 750

19 Today’s reading History of palaeontology: History of earth: Radiometric dating details: Geological time scale:

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