2. The discovery of the past

Georges Cuvier

Charles Lyell

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)

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 (1799-1847) Richard Owen (1804-1892)

How do animals fossilize?

Taphonomy (Greek: tafos: burial; nomos: law)

Living organismDeath

Remains

Exposed remains

Buried remains

Stratinomy

Decomposition DecayBleaching

Delayed burial

Immediate burial

Ginkgo biloba Ginkgo adiantoides

Much less than 1% of all organisms fossilize

Coral fish Coral fish from Jura

FossilMineralization

Bioerosion

A fossil forest in Dorset, England formed by fossilized bacteria around old tree stumps.

Fossilized Cyanobacteria (stromatolites) from South Africa

A mammoth coprolith (fossilized excrements)A fossilized dinosaur footprint from New Mexico

From B. Ziegler: Allgemeine Paläontologie. Thieme, 1975.

Immediate and delayed buriages

Hard body materials Soft body materials

What fossilizes?

Substance Examples

Calcite (CaCO3) OctocoralliaBryozoaBrachiopodaPolychaetaAmmonitaBelemnitaEchinodermata

Aragonite (CaCO3) HydrozoaGastropoda

Calciumphosphate Vertebrata (Ca5(OH)(PO4)3) Trilobita

Crustacea

Opal (SiO2.H2O) RadiolariaDiatomeaPorifera

Chitin AlgaeFungiArthropodaCnidariaPriapulidaAnnelida

Cellulose PlantaeTunicata

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

Vertebrata

Echinodermata

Tentaculata

Arthropoda

Cnidaria

Porifera

Branchiotremata

Annelida

Flagellata

Ciliata

Cephalochordata

Echiurida

Tunicata

Chaetognatha

Plathelminthes

Pentastomida

Nematoda

Tardigrada

Onychophora

Pogonophora

Sipunculida Rhizopoda

Ctenophora

Mesozoa

Sporozoa

Without hard skeleton With hard skeleton

Hard skeleton infrequent

Fossils Fossils

Unknown

Unknown

Rare

Rare

Unknown

Unknown

Rare

Unknown

Rare

Unknown

Rare

Unknown

Unknown

Unknown

Often

Often

Often

Often

Often

Often

Some taxa often

Some taxa often

Some taxa often

Some taxa often

Often

Mollusca Often

How complete is the fossil record?

Under what conditions do organisms fossilize?

Volcanic ashesAnaerobic conditions(moorlands)

River sediments

Moisture gradient

Nutrient rich soils

Probability of fossilization

Salinity gradient

How complete is the fossil record?

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:n

T qT 1 qTT

T 1

P [1 (1 R )(e e )]

Species level: 77%

Genus level: 91%

00.10.20.30.40.50.60.7

0 5 10 15 20 25 30

Me

tric

s

PZ PZ/MZ MZ/CZNZ CZOlder ------ Younger

RCI

GER

SCI

Speciesy = -0.88x + 6.5

Generay = -0.37x + 5.03

0

1

2

3

4

5

6

7

0 2 4 6 8 10 12 14

Actual range

ln R

SCI: Quotient of consistent to inconsistent nodes

RCI: Relative completeness index

GAP: Gap excess index

Divergence time inferred

from cladogram

Divergence time inferred from fossils

Benton MJ, Willis MJ,  &  Hitchin R. 2000. Quality of the fossil record through time. Nature 403: 534-537.

Alba DM, Jordi A, Moya-Sola S. 2001. Completeness of mammalian fossil record in the Iberian neogene. Palaeobiology 27: 79-83

Continental drift

Alfred Lothar Wegener (1880-1930)

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.. 2004. Understanding earth, http://www.whfreeman.com/presssiever/con_index.htm?99iex

From C. R. Scotese: http://www.scotese.com/future.htm

Continental drift

How to match phylogeny and plate tectonics

Tinamou

Moa

Rhea

Ostrich

Kiwi

Emu

Cassowary

New Guinea

Australia

South America

New Zealand

Africa

79

69

65

62

35

100

82

55

0.1

Relative dating methods

Relative dating uses geological strata to infer whether fossils are older or younger than a given stratum

Layer 1

Layer 2

Layer 2

Time

Older

Younger

Stratigraphy

Morphological primitivism

Fossil dating

Absolute dating methods

Radiometric dating

0

0.2

0.4

0.6

0.8

1

0 3.4657 6.9314 10.3971 13.8628 17.3285 20.7942

Time [half times]

De

cay

y

Surviving atoms

Daughter atoms

y=e-kt

t = ln(y)/kHalf time

Radioactive Element Stable element Half timePotassium 40 Argon 40 1.25 billion yrsRubidium 87 Strontium 87 48.8 billion yrsThorium 232 Lead 208 14 billion yearsUranium 235 Lead 207 704 million yearsUranium 238 Lead 206 4.47 billion yearsCarbon 14 Nitrogen 14 5730 years

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

Volcanic rocks

Carbon 14 is used for bones

How to use radiometric dating?

The Rb/Sr System 87 8737 38Rb Sr 87 87 t

t 0Rb Rb e

t 0 t

t tt t t t

P N N

P N e N N (e 1)

b-decay

l = 1.42 x 10-11 a-1,  t1/2 = 4.8 x 1010 a

87 87 t 87t t 0Sr Rb (e 1) Sr

87 87 87tt t 0

86 86 86t t t 0

Sr Rb Sr(e 1)

Sr Sr Sr

87t

86t

Sr

Sr

87t

86t

Rb

Sr

tslope (e 1)

870

86t 0

Sr

Sr

4x x3 xe 1 x ... 1 x;x 1

3! 4!

87 87t 0

87 87 87 86 86t t 0 t t 0

8786 86 86tt t t 0

86t

Sr Sr

Sr Rb Sr Sr Sr1t t

RbSr Sr SrSr

tt 0N N e

Pt: Amount of daughter atoms through decay

Total OriginalDecay

86Sr is an isotope that is

• not radioactive

• not radiogen

Modified from Andy MacRae: Radiometric Dating and the Geological Time Scale. http://www.talkorigins.org/faqs/dating.html

Raw data

Recognition of unique events to subdivide time

Radiomtric dating of layers

Calibrating geological

time

Stratigraphy Relative time scale

Absolute time scale

Geological time scale

Radiometric dating

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.

History of the earth

Nicolas Steno (1638-1686)

Steno founded stratigraphy by stating that

geological layers are horizontal and superposed.

Deeper layers are older.

The Red Rock Canyon, California

The geological time scale

Eon Era Period Age at Base (Mya) Duration (Mya)Phanerozoic Cenozoic Quaternary 1.6 1.6

    Tertiary 65 63.4  Mesozoic Cretaceous 140 75    Jurassic 205 65    Triassic 250 45  Paleozoic Permian 290 40    Carboniferous 355 65    Devonian 410 55    Silurian 440 30    Ordovician 510 70    Cambrian 540 30

Proterozoic Neoproterozoic Ediacaran (Vendian) 630 90    Cryogenian 850 220    Tonian 1000 150  Mesoproterozoic   1600 600  Palaeproterozoic   2500 900

Archean     3800 2950Hadean     4550 750

History of palaeontology: http://en.wikipedia.org/wiki/History_of_paleontologyHistory of earth: http://wiki.cotch.net/index.php/History_of_the_EarthRadiometric dating details: http://www.tulane.edu/~sanelson/eens211/radiometric_dating.htmGeological time scale: http://en.wikipedia.org/wiki/Geologic_time_scale

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