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Classification of Organisms


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Classification of Organisms

Why is classification important?



  • Biologists use a universal language just as groups of people communicate with a universal language.

  • Scientists constantly exchange information at the international level.

  • Organizing the more than 2 million known species is important.


Taxonomy: The science of naming and classifying organisms.
Linnaeus invents a simpler system for classification – binomial nomenclature.
Binomial nomenclature uses a two – word Latin name for every organism. Every species has its own, unique Latin name.
The Latin name consists of a Genus name and a species name.
This two – part name is its Scientific Name.

The Genus name is always capitalized and the species name is always in lower – case. The entire scientific name is always in italics.


All species are classified in a broad classification scheme by placing them in smaller and smaller groups based on similar, shared characteristics.
Each classification group contains species that all share common characteristics. This can help you quickly associate characteristics with a species that you are not familiar with.


The modern classification system uses this hierarchy of groupings.


Note that Kingdom is the most inclusive group. As you move through the classification groupings each group becomes progressively smaller and more specific.

This diagram, for example, shows the classification of the grizzly bear, Ursus horribilis.






Ursus americanus Ursus maritimus







Kingdom:

Animalia

Phylum:

Chordata

Class:

Mammalia

Subclass:

Marsupialia

Order:

Diprotodontia

Suborder:

Macropodiformes

Family:

Macropodidae

Genus:

Species:


Macropus

giganteus



Kangaroo


Scientific classification








Plants, like all living things, are also classified. This is the classification of the Moss rose, Rosa gallica.

Even bacteria are classified according to this classification system.

Staphylococcus aureus






Domain:

Bacteria

Kingdom:

Bacteria

Phylum:

Firmicutes

Class:

Bacilli

Order:

Bacillales

Family:

Staphylococcaceae

Genus:

Staphylococcus

Species:

Staphylococcus aureus





What defines a species?


Do these scorpions

belong to the same

species?
Do these primates

belong to the same species?


Biological concept of species: A group of naturally occurring organisms that interbreeds, or could potentially interbreed and is reproductively isolated from other groups.


Historically, classification based on similarities between species should reflect an organism’s phylogeny. Phylogeny is the evolutionary history of an organism.
However, using these similarities to make evolutionary connections can be misleading.

For example, if we look at bats, butterflies and birds we could reach the conclusion that they are closely related because they all have wings.


What do you think? Are these three organisms closely related on the evolutionary tree of life?


These three “wings” are called analogous structures. Analogous structures serve the same function but are not found on closely related species.
This is an example of convergent evolution – species evolve similar characteristics to adapt to similar habitats.
If we grouped organisms by analogous structures, we would have some very confusing classification systems. For instance, bats would be placed in the same group with butterflies, but bats are much more closely related to us than they are to butterflies. (They are mammals like us.)

Evolutionary Trees

Evolutionary or phylogenetic trees are the traditional method by which taxonomists classify and organize species. This system does take into account the evolutionary relationships between organisms.


Cladistics

Cladistics, a new approach to classification, allows scientists to reconstruct evolutionary relationships through the use of shared characters.
Ancestral characters: ancestral characters are characters that evolved in a common ancestor of all groups “above” on the cladogram.

A derived character is a characteristic that evolved in some groups but not others.


Making Cladograms


Objectives:

Given some groups of organisms and some of their distinguishing characteristics, you will construct a cladogram, and properly interpret and analyze that cladogram in terms of how it shows common ancestry and degrees of evolutionary relationship.


Procedure:

Step 1: Using your textbook and the explanations below, determine which of the characteristics each animal has. In the Data Table provided, place an "+" in the box if the animal has the characteristic, a “-“ in the box if the animal doesn’t have the characteristic, etc.


Explanations of Characteristics:
Set #1: Dorsal nerve cord (running along the back or "dorsal" body surface)

Notochord (a flexible but supporting cartilage-like rod running along the back or

"dorsal" surface)
Set #2: Paired appendages (legs, arms, wings, fins, flippers, antennae)

Vertebral column ("backbone")


Set #3: Paired legs
Set #4: Amnion (a membrane that holds in the amniotic fluid surrounding the embryo; may or

may not be inside an egg shell)


Set #5: Mammary glands (milk-secreting glands that nourish the young)
Set #6: Placenta (structure attached to inside of uterus of mother, and joined to the embryo by the umbilical cord; provides nourishment and oxygen to the embryo)
Set #7: Canine teeth short (same length as other teeth)

Foramen magnum forward (spinal cord opening, located forward, under skull)


Animals

Sets

Traits

Kangaroo

Lamprey

Rhesus Monkey

Bullfrog

Human

Snapping

Turtle


Tuna

1

Dorsal Nerve Cord

Notochord
























2

Paired Appendages

Vertebral Column

























Finish completing the data table in your notebook.


Step 2: Draw a cladogram to illustrate the ancestry of these animals. Be sure to include the shared characteristics as time proceeds.


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