1. Carolus Linnaeus developed the first useful classification system in the mid 1700’s. He
proposed the seven categories still used today. Organisms were considered to be closely related
if they had similar physical appearance. His categories, now called taxons, are grouped from
largest, most inclusive, to the smallest, most specific taxon. The seven taxons are: kingdom,
phylum, class, order, family, genus & species.
Think about this: If Linnaeus had found a legless salamander that lives under ground, how do
you think he might have classified it? Snake? Worm? Lizard?
Take a look at the short video clip for a more detailed introduction to classification:
2. The two smaller taxons were used to develop Binomial (two name) Nomenclature as a way to
identify an organism.
A. Most scientific names are written in Latin and include the genus (always capitalized)
and species (never capitalized); if typed the Genus species name will always be in italics,
if hand written it will always be underlined. Example: Homo sapiens – the scientific
name for humans.
B. Plants and Fungi classification uses divisions rather than phylum names.
C. The science of classification is called Taxonomy.
3. A dichotomous key is a tool that allows the user to determine the identity of items in the
natural world, such as trees, wildflowers, mammals, reptiles, rocks, and fish. Keys consist of a
series of choices that lead the user to the correct name of a given item. "Dichotomous" means
"divided into two parts". Therefore, dichotomous keys always give two choices in each step.
Example of a diagnostic dichotomous key for some eastern United States oaks based on leaf
characteristics
1. Leaves usually without teeth or lobes: go to2
1. Leaves usually with teeth or lobes: go to 5
2. Leaves evergreen: go to 3
2. Leaves not evergreen: go to 4
3. Mature plant a large tree — Southern live oak Quercus virginiana
3. Mature plant a small shrub — Dwarf live oak Quercus minima
4. Leaf narrow, about 4-6 times as long as broad — Willow oak Quercus phellos
4. Leaf broad, about 2-3 times as long as broad — Shingle oak Quercus imbricaria
5. Lobes or teeth bristle-tipped: go to 6
5. Lobes or teeth rounded or blunt-pointed, no bristles: go to 7
6. Leaves mostly with 3 lobes — Blackjack oak Quercus marilandica
6. Leaves mostly with 7-9 lobes — Northern red oak Quercus rubra
7. Leaves with 5-9 deep lobes — White oak Quercus alba
7. Leaves with 21-27 shallow lobes — Swamp chestnut oak Quercus prinus
http://en.wikipedia.org/wiki/Dichotomous_key
4. With modern technology, there are more accurate ways to classify an organism than by
physical characteristics. These are three most commonly used methods:
A. Cladistic analysis – in this method, only the characteristics of organisms that are
evolutionary innovations are considered when selecting which organism are more
closely related to another. These unique characteristics are called “derived”
characteristics. A diagram showing evolutionary relationships is called a cladogram.
A speculatively rooted tree for rRNA genes; shows possible ancestry
http://upload.wikimedia.org/wikipedia/commons/7/70/Phylogenetic_tree.svg
B. Comparative Embryology – By studying the stages in the development of embryo, it is
Inferred that those organisms that show similar development patterns are more closely related.
Examine the illustration below comparing a number of different reptiles, birds and mammals.
Can you spot the differences in development in the middle line of images? Would you have
guessed which animal was which by examining just the first row?
Try this: Scroll down so that only the first row of organisms is visible on your screen.
Challenge your friends or family to guess which is which. Then reveal the second row and test
them again. Were all of the guesses correct? From just row two, if you did not know which was
which, would you be able to guess that the last four are more closely related to each other than to
any of the others?
Comparative Embryology
http://www.biologyreference.com/images/biol_01_img0111.jpg
C. DNA, RNA & Protein similarities can now be determined from small samples of an
organism. DNA fingerprints, similar to the tests performed to determine parentage or
to identify criminals, can make a definite analysis as to how many genes are identical.
The more common genes, the more closely related organisms are.
5. Why do scientists use classification systems? Imagine walking into a grocery store to buy a
can of soup. If the groceries were randomly scattered, with no labels on the cans or boxes, how
would you know where to find the soup that you wanted?
A. Common names vary by region & can be confusing. Different regions may have
different names for the same organism. “Unlike scientific names, common names are not
unique. As a result, common name usage can lead to confusion about what animal is
being referred to and what their relationships are to other animals. An example are
"badgers." There are various animals worldwide that are superficially similar, honey
badgers (Mellivora capensis), North American badgers (Taxidea taxus), Eurasian badgers
(Meles meles), stink badgers (Mydaus javanensis), and ferret badgers (Melogale
personata). Although they are all called "badgers" and they are all members of the same
mammalian family, they are not each other's closest relatives.” Click on the names of the
badgers to learn more and see pictures. Information courtesy of :
http://animaldiversity.ummz.umich.edu/site/animal_names/scientific_name.html
B. Latin is recognized world wide so the name means same thing everywhere.
C. It is easier to communicate about specific organisms with people in other countries
with different languages.
6. Below is the complete classification for humans. Notice that the seven taxons are shown with
an additional sub – taxon, Vertebrata, indicating that all organisms in this group have a
backbone.
Learn the complete classification for humans in preparation for a quiz on these classification
notes.
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•
•
Animalia (Kingdom)
Chordata (Phylum)
Vertebrata (Subphylum) (animals with backbones)
•
Mammalia (Class) [all mammals]
•
Primates (Order)
•
Hominidae (Family)
•
Homo (Genus)
•
Homo sapiens (Species)