Understanding Trees

Pre-test

Which mammal is the pig more closely related to, cow or camel?

Which mammal here is the most primitive?

Fig. 4.8b

•Common ancestor•Root of the tree

•Nodes•Terminal taxa (tips)•Branches

Phylograms and Cladograms

Trees can be built for extinct organisms…

Trees can include lineage “persistence”

Some trees show timing of events

Most trees today are built for extant organisms

only…

Tree Rules

1. Read the nodes, remember they swivel2. Bifurcation rule3. Monophyly snip rule4. Sibling ≠ Ancestor5. Sister lineage snip rule and ages

1. Read the nodes, remember they swivel!

Don’t read left to right or top to bottomRead the nodes, and the nodes swivel

Read the nodes

A B C D

e f

g

For cladograms, some information about timing (e and f after g)

For phylograms,a little more informationabout timing

This tree is ladderized right…Swivel the nodes to make it ladderized leftRedraw it with lungfish at the top

Assignment

2. Bifurcation Rule

• Can only have one divergence event at a time.

• Can’t have two divergence events at the same time (snap two fingers at once)

Breaking the Bifurcation Rule:Hard polytomies and Soft polytomies

Cichlids