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 (1799-1847)
Richard Owen (1804-1892)
How do animals fossilize?
Taphonomy (Greek: tafos: burial; nomos: law)
Immediate
burial
Death
Living organism
Remains
Mineralization
Fossil
Buried remains
Decomposition
Decay
Bleaching
Delayed
burial
Exposed remains
Ginkgo biloba
Stratinomy
Ginkgo adiantoides
Much less than 1% of all
organisms fossilize
Coral fish
Coral fish from Jura
Bioerosion
A fossil forest in Dorset, England formed by
fossilized bacteria around old tree stumps.
A fossilized dinosaur footprint from New Mexico
Fossilized Cyanobacteria (stromatolites) from
South Africa
A mammoth coprolith (fossilized excrements)
Immediate and delayed buriages
From B. Ziegler: Allgemeine Paläontologie. Thieme, 1975.
What fossilizes?
Hard body materials
Soft body materials
Substance
Examples
Calcite (CaCO3)
Octocorallia
Bryozoa
Brachiopoda
Polychaeta
Ammonita
Belemnita
Echinodermata
Aragonite (CaCO3)
Hydrozoa
Gastropoda
Calciumphosphate
(Ca5(OH)(PO4)3)
Vertebrata
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:
Sinosauropteryx
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
Nematoda
Rare
Hard skeleton infrequent
Plathelminthes
Unknown
Branchiotremata
Some taxa often
Ctenophora
Unknown
Annelida
Some taxa often
Mesozoa
Unknown
Ciliata
Some taxa often
Sporozoa
Unknown
Flagellata
Some taxa often
Under what conditions do organisms fossilize?
Moisture gradient
Nutrient rich soils
River sediments
Anaerobic conditions
(moorlands)
Volcanic ashes
Probability of fossilization
Salinity gradient
How complete is the fossil record?
Metrics
Benton MJ, Willis MJ, & Hitchin R. 2000. Quality of the fossil record through time. Nature 403: 534-537.
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
SCI
GER
RCI
Divergence
time inferred
from
cladogram
Divergence
time inferred
from fossils
SCI: Quotient of consistent to inconsistent nodes
0
5
10
15
20
25
30
PZ PZ/MZ NZ MZ/CZ CZ
Older
-----Younger
RCI: Relative completeness index
GAP: Gap excess index
Alba DM, Jordi A, Moya-Sola S. 2001. Completeness of mammalian fossil record in the Iberian neogene.
Palaeobiology 27: 79-83
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:
Neogene Iberian mammals
7
6
ln R
5
n
4
Genera
y = -0.37x + 5.03
3
2
1
0
Species
y = -0.88x + 6.5
0
2
4
6
PT   [1  (1  R T )(e  qT 1  e  qT )]
T 1
Species level: 77%
8
10
Actual range
12
14
Genus level: 91%
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
Continental drift
From C. R. Scotese: http://www.scotese.com/future.htm
How to match phylogeny and plate tectonics
Cassowary
35
62
Emu
New Guinea
0.1
65
Kiwi
Australia
55
69
Ostrich
82
South America
79
Rhea
100
New Zealand
Moa
Africa
Tinamou
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
Absolute dating methods
Radiometric dating
Radioactive Element
Potassium 40
Rubidium 87
Thorium 232
Uranium 235
Uranium 238
Carbon 14
Stable element
Argon 40
Strontium 87
Lead 208
Lead 207
Lead 206
Nitrogen 14
Half time
1.25 billion yrs
48.8 billion yrs
14 billion years
704 million years
4.47 billion years
5730 years
potassium feldspar (orthoclase)
muscovite
amphibole
glauconite
Volcanic rocks
Sometimes in sediments
1
Decay y
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:
0.8
0.6
y=e-kt
t = ln(y)/k
Half time
0.4
0.2
Surviving
atoms
0
0
3.4657
Daughter
atoms
6.9314 10.3971 13.8628 17.3285 20.7942
Time [half times]
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
37
Rb 87
38 Sr
N t  N 0 e lt
87
Rb t 87 Rb0elt
l= 1.42 x 10-11 a-1,
t1/2 = 4.8 x 1010 a
b-decay
Pt: Amount of daughter atoms through decay
Pt  N0  N t
lt
lt
Pt  N t e  N t  N t (e  1)
87
87
86
Srt
Srt
Srt 87 Rb t (elt  1) 87 Sr0
Total
Decay
Original
slope  (elt  1)
87
86
86Sr
is an isotope that is
Sr0
Srt 0
87
•not radioactive
x3 x 4
e  1  x   ...  1  x; x  1
3! 4!
x
•not radiogen
87
Srt

86
Srt
87
Rb t
Srt
86
87
Rb t lt
Sr0
(e

1)

86
86
Srt
Srt 0
87
87
Srt
Sr0

87
87
Srt 87 Rb t
Sr0
1 86 Srt 86 Srt 0
 86
lt  86
t
87
86
Rb t
Srt
Srt
Srt 0
l
86
Srt
Radiometric dating
Stratigraphy
Raw data
Relative time
scale
Recognition of
unique events to
subdivide time
Absolute time
scale
Geological
time scale
Calibrating
Radiomtric
geological
dating of layers
time
Modified from Andy MacRae: Radiometric Dating and the Geological Time Scale. http://www.talkorigins.org/faqs/dating.html
Fission track
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
Dendrochronology analyses treering growth patterns.
History of the earth
Steno founded stratigraphy by stating that
geological layers are horizontal and superposed.
Deeper layers are older.
Nicolas Steno (1638-1686)
The Red Rock Canyon, California
The geological time scale
Eon
Era
Phanerozoic Cenozoic
Mesozoic
Paleozoic
Proterozoic
Neoproterozoic
Mesoproterozoic
Palaeproterozoic
Archean
Hadean
Period
Quaternary
Tertiary
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
Ediacaran (Vendian)
Cryogenian
Tonian
Age at Base (Mya) Duration (Mya)
1.6
1.6
65
63.4
140
75
205
65
250
45
290
40
355
65
410
55
440
30
510
70
540
30
630
90
850
220
1000
150
1600
600
2500
900
3800
2950
4550
750
Today’s reading
History of palaeontology: http://en.wikipedia.org/wiki/History_of_paleontology
History of earth: http://wiki.cotch.net/index.php/History_of_the_Earth
Radiometric dating details: http://www.tulane.edu/~sanelson/eens211/radiometric_dating.htm
Geological time scale: http://en.wikipedia.org/wiki/Geologic_time_scale