Chapter 9 - Taxonomy

Taxonomy – the science of classifying organisms – has two purposes:

• To identify the organism• To represent relationships among them

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History of Taxonomy:

• Aristotle – believed in the “ladder of nature” – sponges were at the bottom and humans were at the top – he classified things as either plants or animals ( see fig.1 pg.326)

9.1 Taxonomic Systems

• Carl Linnaeus- 18th century – he classified organisms based on structure

• The more features organisms have in common, the closer their relationship

He introduced binomial nomenclature: a 2 name system for naming organism using Latin or Greek ( Latin is a dead language)

• Ex. Castor canadensis – beaver • Genus species - the Genus name is

always a capital letter

The 2 names indicate similarities in anatomy, embryology & evolution

ancestry

• Ex. – Ursus americanus (black bear) Ursus horribilis (grizzly bear)

• koala bear Genus: Phascolarctos Species: cinereus

• Panda bear Genus Ailuropoda Species: melanoleuca

Modern Taxonomy

Today we use these major categories and evidence to support classification:

• Fossil records – they provide clues, but are rarely complete.

• Anatomy – a) homologous structures – similar in structure but may have different functions.b) vestigial structures – structures that once had a purpose but no longer serve a function.

• Comparative embryology – ex. – all vertebrates have a stage as an embryo where they look alike.

• Comparative biochemistry – comparing DNA, genes and proteins.

Fossil Records

Homologous Structures

Vestigial Structures

Vestigial hind legs in a python. Evidence that snakes descended from lizzards.

Comparative Embryology

Comparative Biochemistry

Levels of ClassificationOrganisms are classified based on 7

taxa (levels) • Kingdom• Phylum• Class • Order• Family • Genus• Species

Until recently organisms were grouped into 5 kingdoms:

Now it is believed that Monera should be 2 separate kingdoms: Eubacteria

And Archaebacteria

Phylogeny – the history of the evolution of organisms – often shown in a diagram called a phylogenetic tree

– see pg.329

A three Domain system of Classification