BILD 3 Lecture Notes - Lecture 12: Bild, Monophyly, Polyphyly
13 Jun 2018
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BILD 3 Lecture 12
4/30/2018
• Once you have a tree based on a bunch of synapomorphies, then you look at patterns of
specific character states
• Categories of taxonomic groupings according to trait
o Monophyletic
▪ Trait is present in all members of a group with a common ancestor
▪ E.g. placental mammals are monophyletic, while egg and pouch animals
are’t
▪ A monophyletic group is also called a clade; a clade is all descendants of a
common ancestor
▪ E.g. archosaurs are monophyletic→includes some dinosaurs,
crocodilians, and birds
o Paraphyletic
▪ Trait is present in some but not all members of a group that share a
common ancestor
▪ Likely explanation: present in each lineage, but lost to one species
▪ E.g. fish, features like scales and gills are lost in amphibians and mammals
▪ E.g. reptiles; mammals and birds have lost classic reptile characteristics
(i.e. cold-blooded, soft egg shells, and scaly skin)
o Polyphyletic
▪ Trait is preset i speies that do’t share a oo aestor with the
trait
▪ Is sometimes analogous
▪ E.g. warm-blooded animals, was independently evolved in birds and
mammals→not a common ancestor of birds and mammals that was
thought to be warm-blooded
▪ E.g. wings and bipedalism
• Characteristics that are similar because of convergence, are not
passed down from a common ancestor
▪ Often due to convergent evolution
• Why are character states similar or conflicting?
o Homology: character shared due to inheritance of traits form a common
ancestor
▪ E.g. oe struture of a tetrapod’s li
▪ Homologies can be ancestral or derived characters
• Backbone- shared ancestrally conserved character for birds;
present in related clades; reversals or loss of traits can be
common in ancestrally derived characteristics
• Feathers- shared derived character for birds; evolutionary novelty
unique to a clade- ancestral, but not deeper than this clade
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