A. The Fossil Record

The Law of Succession

pygmy armadillo

fossil glyptodont fossil Diprotodon

wombat

The Fact of Extinction

Fig. 22-3 Campbell and Reece

Younger stratumwith more recentfossils

Layers of depositedsediment

Older stratumwith older fossils

Rivers carry sediment into seas and swamps

Fig. 22-15

Bristolia insolens

Bristolia bristolensis

Bristolia harringtoni

Bristolia mohavensis

Latham Shale dig site, SanBernardino County, California

Dept

h (m

eter

s )

0

2

4

6

8

10

12

14

16

18

1

2

3

3

3

1

2

44

Fig. 25-4Present

Dimetrodon

Coccosteus cuspidatus

Fossilizedstromatolite

Stromatolites Tappania, aunicellulareukaryote

Dickinsoniacostata

Hallucigenia

Casts ofammonites

Rhomaleosaurus victor, a plesiosaur

100

mill

ion

year

s ago

200

175

300

270

400

375

500

525

565

600

3,50

0 1,

500

2.5 cm4.5 cm

1 cm

Fig. 25-5 Campbell and Reece

Time (half-lives)

Accumulating “daughter” isotope

Remaining “parent” isotopeFr

actio

n of

par

ent

isoto

p e re

mai

ning

1 2 3 4

1/2

1/41/8 1/16

Bias in the fossil record:Preservation biasTemporal bias

Trends in Evolution

Cope's rule: evolution tends to increase body size over geological time in a lineage of populations.

Figure: over the last sixty million years, the average weight of horses has increased ten fold.

Understanding the type of trend (passive or driven) is importantDon’t over-interpret too much about mechanismsSelection can be going on in a passive system or in a driven one…