The Tree of Life/Phylogeny (L9 + L10)

Exam 2 Lectures 9 and 10

Epigenetics

The study of how behavior/environment can cause genes to be turned on or off without altering the genetic code itself.

Monophyletic group

a group in a phylogenetic tree that includes a common ancestor and all of its descendants

Paraphyletic group

a group in a phylogenetic tree that includes a common ancestor and some of its descendants

Polyphyletic group

a group in a phylogenetic tree that does not include a common ancestor

Taxonomic hierarchy

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species

Homologous characters

characters that are the same due to common descent

Homoplasy

Characters that are the same due to convergent evolution or evolutionary reversal

Principle of parsimony

The best-fit phylogenetic tree is the one with the fewest number of changes.

Fossil types

• Trace fossil - (footprints, burrows, feces)

• Molds and casts - (an impression of an organism and a mold filled with sediment)

• Replacements - (original material replaced with crystals)

• Petrified/Permineralized - (empty pore spaces are filled in by minerals)

• Amber - (preserved tree sap trapping an organism)

• Original material - (mummification or freezing)

• Molecular fossils - (DNA, proteins, lipids)

Burgess shale

A sedimentary rock formation containing many marine fossils from 500 mya

Messel shale

A large collection of fossils in Germany formed when toxic gas was released from a giant lake and suffocated nearby animals.

• Many fossils here retained feathers/fur

Biogeography

The study of the distribution of species and ecosystems in geographic space and through geological time.

Ex: Groups evolved before Pangaea are distributed worldwide, while groups that evolved after are only in certain continents.

Archaeopteryx

A transitional fossil between modern birds and dinosaurs

Tiktaalik

A transitional fossil between modern tetrapods and fish (transition happened around 370 mya)

Lucy

A transitional fossil between chimpanzees and humans. (smaller brain, but bipedal)

Phylogenetic tree pieces

Character

An identifiable heritable trait

Ex: wings

Character state

the condition of the character

Ex: “present” or “absent”

Reconstructing phylogeny

0 = ancestral

1 = derived

Polytomy

when it can’t be determined which members of the branches are most closely related

Teleosts

Ray finned fish

Coelacanths

lobe-finned fish, homologous to tetrapod limbs.

Mammalian ear bones

• come from reptile jaw bones (Homologus)

• are composed of 3 bones

Feathers

• Originally evolved for warmth and species recognition

• an example of an exaptation

Exaptation

A shift in the function of a trait during evolution

Ex: Hair/feathers

Heterochrony

evolutionary change in form due to a change in growth rate/timing of developmental events

• can produce a new final shape