09 - 4/8/09 Principles of classification Cladistics o A...

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4/8/09 Principles of classification Cladistics o A “last common ancestor” is assumed, but not specified; o Only particular derived traits are considered diagnostic of distinct evolutionary lineages o No time frame specified A brief clarification o Wolves did not “become” dogs o Monkeys did not “become” humans o Common ancestors of these species gave rise to modern forms Kinds of traits in cladistics o Derived, or modified, traits Unique to a taxonomic group Distinguished it from other groups o Primitive, or ancestral, traits: Inherited from common ancient ancestor Shared with all living relatives 5 digits in humans and turtles o groupings based on shared derived characters a cladogram The K/T extinctions o End of the Cretaceous Period About 65 mya 50% of living genera disappear
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most of the dinosaurs o a metero 10km (6.2m) in diameter, in the Ycatan first extinctions occurred within 1 week of impact
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09 - 4/8/09 Principles of classification Cladistics o A...

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