Evidence for evolution: Fossils

John Murray

Evidence for evolution: Fossils

As told by a series of

&

papers

Oxford Dictionary:

“the remains or impression of a prehistoric plant or animal embedded in rock and preserved in petrified form””a person or thing that is outdated or

resistant to change”

Fossils

Usually formed from hardest, most resistant parts of organisms

(but not always)

Sedimentary rocks

Fossil record is incomplete

Fossils

(1) Organismic Incompleteness

Fossil record is incomplete

Fossils

Fossil record is incomplete

(2) Stratigraphic Incompleteness

Effect of varying rates of deposition on apparent rates of change in the fossil record. The numbers refer to

equal lengths of time.

Fossils

Fossil record is incomplete

(3) Ecological Incompleteness

Fossils

49Ma: Grube Messel

Fossil record is incomplete

So why bother at all with fossils?

1. Tangible evidence for evolution

2. (Palaeo) ecology & ethology

3. Evolutionary rates

4. History of Life

Fossils

150Ma: Solnhofen

A snapshot

1.Tangible evidence

for evolution

Caudipteryx zoui

2. (Palaeo)ecology & ethology

1859: Darwin’s Origin of Species

3. Evolutionary rates

time

morphology

Darwinian view:

‘Classical’ Phyletic

gradualism

time

morphology

Key points: Evolutionary rates remain

constant through speciation event.

Small changes seen gradually through

generations. Darwin’s ‘Paradigm’

1970s: Eldredge & Gould:

Punctuated Equilibrium

Punctuated Equil ibrium

time

morphology

Key points:• Evolutionary

rate very low (0) over long periods • Speciation in

short periods of time with rapid rates of change.• Eldridge &

Gould argued that this model most closely resembles the evidence from fossil record.

Debate about which model is more appropriate has continued to present

Punctuated EquilibriumPhyletic Gradualism Vs

15,000 trilobites!

Peter Sheldon

4. History of Life

History of E a r t h

Base of Palaeogene

Terrestrialisation

Zachelmie trackway

Evolution & the tree of life

(the state of the art)

Phylogenetic tree:Lancelet(outgroup)

Lamprey

Bass

Frog

Turtle

Leopard

Vertebralcolumn

Hinged jaws

Four walking legs

Amnion

Hair

Fossils?

Time?

Stem Group

Crown Group

Origin of major animal groups (Phyla)

(Stem – Crown groups get really tricky here!)

Erwin et al. Science 334, 1091-7 (2011)

4. History of Life

Fig. 3. Detailed stage-level depiction of the animal fossil record as compared to the molecular divergence estimates for 13 different animal lineages. Shown in thick black lines are the known fossil records of each of these 13 lineages through the Cryogenian-Ordovician; most lineages make their first appearance in the Cambrian, consistent with the known fossil record of all animals. Further, the extent of these stratigraphic ranges closely mirrors the molecular estimates for the age of each of the respective crown groups (red colored circles), highlighting the general accuracy of the molecular clock. Only cnidarians have an unexpectedly deep crown-group origination as estimated by the molecular clock, as the deep demosponge divergence is apparent from taxon-specific biomarkers (gray bar).

Erwin et al. Science 334, 1091-7 (2011)