Lecture 8: cladistics

Question 1

cladistics

Answer 1

formalized process of determining evolutionary relationships (phylogenies)
- Step 1: determine which taxa you want to include in your tree
- Step 2: create a matrix describing as many relevant character traits as possible
- Step 3: use matrix to infer evolutionary relationships
- Traditionally done using parsimony: what evolutionary tree requires the smallest number of changes but now done with more complex mathematical models of evolution
- Results in cladogram: an evolutionary tree (phylogeny) made from cladistic analyses
- Dinosaurs have traditionally been divided into 2 groups: Ornithischians and Saurischians with the shape of the pelvis a synapomorphy dividing them

Question 2

comparative anatomy

Answer 2

the study of similarities and differences between species
- Ex: first dinosaur, Iguanodon, given the name b/c its teeth were similar to an iguanas
- Limitation: only as good as the things you have to compare your specimen to

Question 3

monophyletic clade

Answer 3

group made up of a common ancestor and all its descendants
- The traits shared between members of a monophyletic group and are unique to the group become hypothesized synapomorphies
- Paraphyletic group: made up of a common ancestor and some but not all of its descendants => useful for constraining the ancestral condition

Question 4

phylogeny

Answer 4

evolutionary tree of dinosaurs
- Problems: there are many members so not sure which species is the ancestor of dinosaurs (very vague)

Question 5

root

Answer 5

the very first point, the hypothetical ancestor

Question 6

taxon

Answer 6

any unit used in the biological classification of life (taxonomy), can be populations, species, or larger clades