Biology Lecture No. 18: Macroevolution
(Wednesday, November 16, 2011)
RECALL (Phylogenetic Analysis):
-Only synapomorphies are informative (not all similarities are homologies, not all homologies are
-Homoplasy is misleading in that it can create similarity between distantly related groups (convergence)
and can erase similarity between closely related groups (divergence).
-Most parsimonious tree (fewest evolutionary steps) is usually the best.
Phylogenies Help Classify Life:
-Many currently-recognized “groups” are not monophyletic and thus “good” groupings.
-Monophyletic: The inclusion of all descendants of the group’s most recent common ancestor.
-E.g. crocodilians share a closer common ancestor with birds than with lizards.
Other Non-monophyletic Groups:
-Prokaryotes: Eukaryotes are more related (share a closer common ancestor) with Archaea than with
-Fish: Fish are more related to reptilians than with sharks.
-Birds: Birds are more related to crocodilians than with mammals, despite them being endotherms.
Patterns In Macroevolution:
-The fossil record, the mode and tempo of evolution, and evolutionary trends (such as changes in body
size) are all common patterns in macroevolution.
Age Of Fossils:
-Law of superposition states that whenever a sedimentary rock formation remains undisturbed, the
bottom are older than top.
-Therefore one reads rock strata from bottom to top and