Review—Evolution and PhylogenyLecture 6a

Phylogeny• Phylogeny—the evolutionary history of groups

of species– Ranges from major lineages (e.g. orders) to species– Primitive groups at right, more recently evolved

groups at left Ancestor (extinct)

Phylogenetic Tree

Phylogeny• Groups arranged based on evolutionary

relatedness• Branching points represent common ancestral

species– Almost always extinct• Evolutionary time millions of years

Ancestor (extinct)

Phylogeny—outgroups• All groups have shared ancestral characters– Example: chordates notochord, bilateral symmetry, etc.

• Outgroups branch off to right– Represent groups with ancestral traits• Primitive—“living fossils”

Ancestor (extinct)

Phylogeny—synapomorphy• Synapomorphy—a newly evolved trait that all

descendent groups possess– Derived Trait—not present in outgroups• Arise slowly—one at a time• Phylogentic trees simplified

Ancestor (extinct)

Ctenoid scalesThoracic pelvics

Physoclistous

Phylogeny—secondary losses/gains• Secondarily lost or gained traits occur in

outgroups– While outgroups represent ancestral

condition, they have still evolved• They are not the original species

Ancestor (extinct)

Lost: eyesGained: slime glands

Phylogeny—vertebrate evolution• Fish are essential to understanding

vertebrate evolution– Outgroups represent a snapshot• Incremental steps

– Most major lineages (outgroups) are extinct

Ancestor (extinct)

Fish Fossil Record• Extinct lineages studied from fossils may be

added to phylogenetic trees

Monophyletic vs. Paraphyletic

• Monophyletic—a group of organisms that share a common ancestor, and all descendents of that ancestor are in the group

• Paraphyletic—sharing a common ancestor, but not all descendents in group

A CB D E F A CB D E FFamilies

Monophyletic Paraphyletic

Ancestor (extinct)

Monophyletic vs. Paraphyletic

Arranging a phylogeny is a matter of perspective• Lobed finned fishes often the ingroup• Major split in vertebrate evolution