BIOL1020 - Week 10

fossils

• remains of once-living organisms

• preserved in sedimentary rocks

• provide evidence for evolution

how do fossils form

• organism is buried in sediment

• molecules replaced by minerals

• usually only parts are preserved

main types of fossils

• trace fossils: activity

• molecular fossils: preserved organic molecules

how do fossils help us understand evolution

• provides evidence for phylogenies

• show patterns of change over time

• helps date evolutionary events

• gives info about extinct speices

transitional fossils

• show traits of both ancestral and derived groups

• provide evidence of evolutionary transitions

• help explain how major changes occured

how do fossils help with timing in evolution

• provides a time scale for phylogenies

• relative dating: rock layers

• absolute dating: radioactive decay gives exact age

mass extinction

when >50% of species go extinct in a short time

causes and impacts of mass extinctions

causes

• climate change

• volcanic activity

• asteroid impacts

• ocean changes

impacts

• change direction of evolution

• take 5-100 million years to recover

• creates new ecological opportunities

adaptive radiation after extinction

where surviving species expand into empty niches and leads to rapid diversification

6th mass extinction

• holocene (right now)

• caused by humans: habitat loss, hunting, climate change

• extinction rate 100-1000x higher than normal

phylogeny and parts of the phylogeny tree

• evolutionary history with branching

• shows how species are related

• parts:

  • root: common ancestor

  • node: speciation event

  • branch: evolutionary lineage

  • tips: current species

main types of groups in phylogeny

• monophlyetic: ancestor and all descendants

• paraphyletic: ancestor and some descendants

• polyphyletic: organisms from different ancestors

homology vs. analogy

• homo: shared due to common ancestry

• ana: similar but evolved independently

synapomorphies

• shared derived traits

• inherited from common ancestor

cladistics

method of building trees using synapomorphies

taxonomy and its hierarchy

• naming and classifying organisms

  • domain

  • kingdom

  • phylum

  • class

  • order

  • family

  • genus

  • species

outgroup

• group that branched off earlier

• used to root the phylogenetic tree

• helps compare traits and determine ancestral vs. derived traits