1. Unit 10: Speciation
10.4 Classification

2. Finding Order in Diversity
Classification is the arrangement of organisms into orderly groups based on their similarities
Classification is also known as taxonomy
Taxonomists are scientists that identify and name organisms.

3. Benefits of Classifying
Accurately and uniformly names organisms.
Prevents misnomers such as starfish and jellyfish that aren’t really fish
Uses the same language (Latin or some Greek) for all names

4. Aristotle’s system
The Greek philosopher Aristotle grouped all the organisms he knew into two groups: plants and animals.
He grouped organisms according to their physical structures and their habitat: land, sea, or air dwellers.
As time passed, more organisms were discovered and some did not fit easily into Aristotle’s groups, but many centuries passed before Aristotle’s system was replaced.

5. Linnaeus’s System of Binomial Nomenclature
18th Century Taxonomist
Classified organisms by their structure
Developed the naming system still used today: binomial nomenclature
Two word name (Genus and species)
Latin or Greek
Italicized in print
Capitalize genus but not species
Underline when writing

6. Binomial Nomenclature
Which TWO are more closely related?

7. Classification Groups
Taxon (taxa-plural) is a category into which related organisms are placed.
There is a hierarchy of groups (taxa) from broadest to most specific
Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species

8. Modern evolutionary Classification
Because classifying organisms based on structure could be problematic, biologists now group organisms into categories that represent lines of evolutionary descent.
We look for homologous structures, similar embryo development, and molecular similarities in DNA, RNA, or the amino acid sequence of proteins.
Remember that the more two organisms share in common-the more closely related they are.

9. Crabs, Barnacles and Limpets
Example
Crabs, Barnacles and Limpets
Until about 150 years ago, barnacles and limpets were grouped together because both had conical shells.
However, we now group them because they share important evolutionary characteristics, such as: a segmented body and an exoskeleton that the organisms molts. Limpets do not share these characteristics.

10. Classification Using Cladograms
A cladogram is a diagram that shows how organisms are related based on shared and derived characteristics.
A derived characteristic is one that appears in recent parts of a lineage but not in its older members.
Examples: feathers, hair, or scales.
They show a probable evolution of organisms from ancestral groups.

11. Dinosaur Example Allosaurus Velociraptor Robin Archaeopteryx Sinornis
Theropods
Feathers with
shaft, veins,
and barbs
Flight feathers;
arms as long
as legs
3-toed foot;
wishbone
Down
feathers
Light bones