taxonomy

Why Classify?

To study the diversity of life, biologists use a

classification system to name organisms &

group them in a logical manner.

Why common names don’t work

Common names vary among languages.

Example:

United Kingdom – Buzzard refers to a hawk

United States – Buzzard refers to a vulture

Early Taxonomists

2000 years ago, Aristotle (384 BC-322 BC) was the first taxonomist

Aristotle divided organisms into plants & animals

He subdivided them by their habitat ---land, sea, or air dwellers .

Early scientists used common names to identify organism.

Examples of common names:

Seahorse, starfish, sealion, jellyfish

Carolus Linnaeus

(1707 – 1778)

Classified organisms by their structure

Created the system of naming we use today.

His classification system includes 7 levels.

In taxonomy, a group or level of organization is called a taxonomic category or taxon.

To avoid confusion, Carolus Linneaeus devised a naming system based on physical characteristics (structures)

Binomial Nomenclature

“Bi” means 2

“nomial” means naming

Nomenclature means “the system of naming”

Defined:

In binomial nomenclature, each species is assigned a two-part scientific name.

Example of Binomial Nomenclature:
Polar Bear is Ursus maritimus

Ursus: genus

Ursus contains 5 other kinds of bears

maritimus: species

The Latin word, maritimus, refers to the sea.

Polar bears often live on pack ice that floats in the sea.

Genus n Species

Genus: is a group of closely related species

Species: Group of similar organisms that can breed and produce fertile offspring

classifcation system

Kingdom – Largest group; contains related phyla (least closely related).(share a less of characteristics)

Phylum – Group of related classes.

Class – Group of similar orders.

Order – Group of similar families.

Family – Group of related genera (plural of genus).

Genus – Group of related species with common traits.

Species – Organisms that can interbreed and produce fertile offspring (most closely related).

The level of classification that contains organisms most closely related is species.

The level of classification that contains organisms least closely related is kingdom.

Rules of the Game

Uniqueness: Every name must be unique.



Universality: Zoologists have adopted, by international agreement, a single language to be used on a worldwide basis.

All animals are given a generic (common name) and specific name in Latin (scientific name).

These names are in italics or are underlined

(i.e. Homo sapiens or Homo sapiens).

Genus species

If these three species belong to the same genus, they are descended from a common ancestor.

A Problem with Traditional Classification

Traditional classification systems relied on

body structure comparisons only

Due to convergent evolution, organisms that are quite different from each other evolve similar body structures.

Convergent Evolution: Process by which unrelated organisms independently evolve similarities when adapting to similar environments.

Example: The Crab, The barnacle, & The limpet

The barnacle and the limpet have similarly shaped shells & look alike

The crab has a very different body form

Based on anatomy, the barnacle & limpet could be classified together and the crab in a different group.

Evolutionary Classification

Biologists now group organisms into categories that represent lines of evolutionary descent, not just physical similarities

Evolutionary Classification: Is the strategy of grouping organisms together based on their evolutionary history.

Cladogram: A diagram that shows the evolutionary relationships among a group of organisms.

Phylogeny

Phylogeny is the presumed evolutionary history of an organism.

The phylogeny of related organisms can be illustrated using a phylogenetic tree.

The Three-Domain System

Organisms used to be loosely classified into 3 categories: Plants, Animals and Monera (bacteria)

Recently, as evidence about microorganisms continue to accumulate, biologists came to realize that the Kingdom Monera were composed of 2 distinct groups of bacteria.

The 6-Kingdom system of classification includes kingdoms:

1. Eubacteria 2. Archaebacteria 3. Protista

4. Fungi 5. Plantae 6. Animalia