Classification and phylogeny of animals

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Classification and phylogeny of animals Over 1.5
million species have been named Estimates this
represents only about 20 of all living
species Only about 1 of all species that ever
lived are on the Earth today
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Some combinations of features have never
been seen How do we classify animals? features
in common usefulness to humans evolutionary
features what are their homologies and
how did they acquire them?
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Phylogeny evolutionary history of species and
closely related species Systematics evolution
of biological diversity How is this
studied fossil record biogeography mass
extinctions
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Systematics also includes taxonomy Formal system
of naming and classifying species The more
recent their common ancestry, the more features
they have in common the more closely they are
grouped Taxonomy predated the study of
evolution systematics is a very dynamic study
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Carolus Linnaeus developed modern scheme of
classification Hierarchical system, from very
specific to increasingly inclusive Standard
taxonomic ranks Linnaeus used binomial
nomenclature
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How is grouping achieved? Phylogenetic tree
includes modern and extinct species Variables
to consider characters- features that vary
among species were similar features inherited
from a common ancestor? if so- homology if
not- homoplasy
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How do we get to this point? Fossil
record Comparative anatomy DNA/proteomic
analysis Cladistics- making dichotomous
comparisons clades can be nested All members of
a clade must be related
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How do we know?
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Homology or analogy? Shared ancestry or
convergent evolution?
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Constructing a cladogram Shared primitive
character backbone separates vertebrates from
other animals Shared derived character hair
separates mammals from other vertebrates Backbon
e can be a derived character that separates
vertebrates from other animals!
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This kind of analysis is not confined to
anatomy Macromolecules (enzymes, other
proteins) amino acid sequences DNA
sequences Parsimony- the fewer differences, the
more recently they diverged
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All of these trees are speculative The best is
the one that accommodates ALL of the available
data
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Analogy vs. homology
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Cladistics establishes sequence of
divergence but not the extent of
divergence Molecular analysis contributes
information about when divergence occurred (see.
P. 504) Fossil analysis do data always
agree? example mammals first appeared 220
million years ago, but did not proliferate until
much later more fossils needed?