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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