Tree thinking and phylogenetic trees

Question 1

What do phylogenies represent?

Answer 1

The lineage of the evolutionary relationships between species

Question 2

Why are phylogenies so useful?

Answer 2

They are useful for looking at common ancestors and identifying where shared traits emerged between species

Question 3

What do we really mean when we say a living animal is “primitive”?

Answer 3

A primitive animal displays ancestral traits or resembles an ancestral species

Question 4

3 criteria for identifying homologous structures + the ONE exception

Answer 4

Position, numerous features in common, historical (fossil) / developmental (embryonic) intermediates

Exception: “function” and “origin/insertion” for muscular system

Question 5

Plesiomorphic trait: definition + example

Answer 5

Plesiomorphic: earlier or ancestral state, links with common ancestors.

Example: notochord, pharyngeal gill slits

Question 6

Apomorphic trait: definition + example

Answer 6

Apomorphic: later or descendant state, distinct in groups.

Example: evolution of middle ear bones in mammals, feathers in birds, secondary palate in crocs and mammals

Question 7

Synapomorphy: definition + example + how to map it

Answer 7

Definition: shared trait between two or more organisms that is derived from a common ancestor

Example: vertebrate column in vertebrates, producing milk in mammals

Mapping: mark a slash before the most recent common ancestor

Question 8

Clade

Answer 8

All organisms in a lineage plus a common ancestor; monophyletic

Question 9

Grade

Answer 9

Organisms sharing certain characteristics but do not form a natural evolutionary unit

May not include some descendant groups

Not monophyletic

Question 10

Monophyletic taxon

Answer 10

Includes most recent common ancestor and all its descendants

Question 11

Polyphyletic taxon

Answer 11

Doesn’t include most recent common ancestor

Question 12

Paraphyletic taxon

Answer 12

Doesn’t include all descendants

Question 13

Sister taxon

Answer 13

The closest relatives of a given taxonomic group

Question 14

Polytomy

Answer 14

An unresolved node with more than two branches, indicating uncertainty about these branches evolutionary relationships

Question 15

Root

Answer 15

Beginning of phylogeny

Question 16

Outgroup

Answer 16

More distantly related group of organisms that serves as a reference group when determining the evolutionary relationships of the ingroup