A. The Fossil Record

The Law of Succession pygmy armadillo fossil glyptodontfossil Diprotodon wombat

The Fact of Extinction

Fig Campbell and Reece Younger stratum with more recent fossils Layers of deposited sediment Older stratum with older fossils Rivers carry sediment into seas and swamps

Fig Bristolia insolens Bristolia bristolensis Bristolia harringtoni Bristolia mohavensis Latham Shale dig site, San Bernardino County, California Depth (meters)

Fig Present Dimetrodon Coccosteus cuspidatus Fossilized stromatolite Stromatolites Tappania, a unicellular eukaryote Dickinsonia costata Hallucigenia Casts of ammonites Rhomaleosaurus victor, a plesiosaur 100 million years ago ,500 1, cm 4.5 cm 1 cm

Fig Campbell and Reece Time (half-lives) Accumulating “daughter” isotope Remaining “parent” isotope Fraction of parent isotope remaining /21/2 1/41/4 1/81/8 1 / 16

Bias in the fossil record: Preservation bias Temporal 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 important Don’t over-interpret too much about mechanisms Selection can be going on in a passive system or in a driven one…