Review—Evolution and Phylogeny Lecture 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 scales Thoracic 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: eyes Gained: 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 AC B DE F AC B DE F Families 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