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Biological Classification |
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Background |
There are a great many
things in the world and names provide us with the means to
identify them. They can be very general, such as
"building." Humans tend to group similar things
together into classifications, such as "houses,"
"stadiums" or "factories."
So it is with living things. Informal
classifications are often superficial and misleading. For
example, the term "fish" is common to many living
things, such as "shellfish," "crayfish" and
"starfish," but a careful examination will reveal
there are many anatomical differences between them.
Biologists attempt to classify or group living things by a
natural system based on anatomical differences. As more
and more knowledge becomes available, classifications are
constantly updated to more accurately reflect it.
The first formal system of biological
classification was developed by Aristotle, the Greek philosopher,
who
virtually invented the science of logic. For 2,000 years,
such classification was part of that system. Carolus
Linnaeus, the Swedish botanist, is regarded as the founder of
the modern system of biological classification. In 1768,
he drew up rules for assigning names to plants and
animals. He was the first to consistently use binomial nomenclature.
A species was living organism capable of reproducing fertile
offspring. Each such species was given a two part
name. People in different countries spoke different
languages. Linnaeus wanted his names to be universally
consistent, so he based them on ancient Latin, the language of Aristotle
and of scholars. Human beings were named Hmo sapiens.
Linnaeus introduced the standard hierarchy of biological
classification cited below. He also developed
workable keys that made it possible to identify plants and
animals from this books. |
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The
Biological Classification System |
All
living things are first divided into very large, very general
classifications. They, in turn, are divided into
increasingly more specific classifications. The basic
Biological Hierarchy of Ranks is Kingdom, Phylum, Class, Order,
Family, Genus and Species. In practice, there are also
many interim classifications, such as superclass and
subclass.
The
following chart shows the classification of human beings and a
white pine tree. |
| Classification |
Animals |
Plants |
| Kingdom |
Animalia |
Plantae |
| Phylum |
Chordata |
Tracheophyta |
| Class |
Mammalia |
Pteropsida |
| Order |
Primates |
Coniferales |
| Family |
Hominidae |
Pinaceae |
| Genus |
Homo |
Pinus |
| Species |
Homo sapiens
(man) |
Pinus strobus
(white pine) |
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Kingdoms |
The
broadest classification unit is the "Kingdom." At
first , there were only two: the Plant Kingdom and the Animal
Kingdom. The microscope resulted in the discovery of very
tiny organisms. This resulted in two additional
kingdoms. The kingdoms are:
| Kingdom |
Contains |
| Procaryota |
Virus, bacteria, and blue-green algae. |
| Protista |
Protophyta, unicellular algae, protozoa
and fungi. (Some botanists classify fungi as a 5th
kingdom). |
| Plantae
(Metaphyta) |
All other plants. Includes true
algae, mosses, ferns, conifers and the flowering
plants. |
| Animalia
(Metazoa) |
The higher animals. Includes
sponges, coral, worms, mollusks, arthropods, and
vertebrates. |
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Phylum |
| Kingdoms are
then divided into Phylum. Most biologists recognize
twenty-eight such phylum in the Animal Kingdom. The most
well-known are listed below: |
| Phylum |
Contains |
| Arthropods |
Animals with external skeletons, such as
crustaceans (lobster, crab, etc.) spiders and the true
insects |
| Mollusks |
Animals with external shells, such as
snails. The sea snails are know for their
beautiful seashells. |
| Chordata |
Animals that generally have a spinal cord. They
include birds, fish, reptiles and mammals. |
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Subphylum |
| There are so many
chordates that they have organized into three subphylum |
| Subphylum |
Contains |
| Tunicates |
Marines creatures that are embedded in a
tough tunic. |
| Cephalochordates |
Fishlike marine invertebrates. |
| Vertebrates |
Animals with a spinal cord. They
include birds, fish, reptiles and mammals.
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Class
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| Class |
Contains |
| Agnatha |
Hagfish and lampreys. |
| Placodermi |
Placodermi - Extinct fish-like creatures. |
| Chondrichtyes |
Sharks, rays and skates |
| Osteichthyes |
Bony Fish |
| Amphibia |
Amphibians |
| Reptilia |
Reptiles |
| Aves |
Birds |
| Mammalia |
Mammals |
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Subclass |
| The reptilia are divided into six subclasses |
| SubClass |
Contains |
| Anapsida |
Turtles, tortoises and terrapins |
| Lepidosauria |
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| Diapsida |
Ruling reptiles - the dinosaurs |
| Synaptosauria |
Extinct |
| Ichthyopterygia |
Extinct fish like animals |
| Synapsida |
Extinct mammal like animals. |
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