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(Sources include Mayr, E. 1969. Principles of Systematic Zoology. McGraw-Hill: New York.)
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Introduction |
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(Sources include Mayr, E. 1969. Principles of Systematic Zoology. McGraw-Hill: New York.)
Welcome! It is 1:04:34 AM on Thursday, October 18, 2018. This page has served 514487 visitors. Last Update: Wednesday, May 7, 2014.
Introduction |
We use this lab in Patterns and Processes, Evolution of Past & Present Ecosystems, and Tropical Marine Ecology. This exercise illustrates the creativity involved in taxonomy and the roles form and function, ancestral traits and derived characters play in generating classification schemes. It can also serve as an introduction to topics in evolution and paleontology. We have noticed that in the field, after completing this exercise, students begin to recognize distinctions and similarities in fauna which they may have not noticed before.
| Phylogeny | Divergence | Convergence |
| Linnaeus | Heirarchy | Evolutionary Tree |
| Homologous Structure | Morphology | Function |
Background |
It has become apparent to scientists that the biosphere consists
of, at a minimum, 1.5 million described species. Some researchers
estimate that there may be upwards of 40 million species (Go here
for an Index of Animal Phyla) alive today! The species alive today are only a very small percentage
of the perhaps billions of species which have lived on this earth
since life first evolved over 3.5 x 109 years ago. Over 75% of
the described extant species belong to the Phylum Arthropoda,
which includes such diverse organisms as lobsters, barnacles,
hermit crabs, crabs, scorpions, shrimp, horseshoe crabs, spiders,
mites, millipedes, and insects. The insects are by far the most
abundant arthropods. How are the many species of insects (for
that matter, all animals and plants) arranged, categorized, and
classified? How does the classification scheme reflect phylogenetic
relationships? It can be a bewildering yet extremely interesting
problem. Taxonomy (Gr. taxis, "arrangement, order", nomos, "law") is the science, laws, or principles of classification
(Latin, classis, "a class", facere, "to make").
The Role of Taxonomy |
1. Taxonomy works out for us a vivid picture of the existing organic
diversity of the earth.
2. Taxonomy provides much of the information permitting a reconstruction
of the phylogeny of life.
3. Taxonomy reveals numerous interesting evolutionary phenomena.
4. Taxonomy supplies classifications which are of great explanatory
value in most branches of biology and paleontology.
For More Info and Excellent Resources on Taxonomy, please see: Internet Resource Guide for Zoology: Systematics, taxonomy & nomencalture
Rules of the Game |
Without a set of international rules to follow, the results of
taxonomy would be confusing at best. The rules of zoological nomenclature
are contained in a document known as the International Code of
Zoological Nomenclature (ICZN). The object of the code is to promote
stability and universality in the scientific names of animals.
All names must be unique, universal, and show stability.
Uniqueness Every name has to be unique. If several names have
been given to the same taxon, priority decides which name will
be the valid name.
Universality Zoologists have adopted, by international agreement,
a single language to be used on a worldwide basis. All animals
are given a generic and specific name in Latin. These names are
in italics or are underlined (i.e. Homo sapiens).
Stability The ICZN attempts to prevent the frequent changing of
names to provide stability.
Classifications - The Linnaean Hierarchy |
Although rudimentary biologic classification may predate civilization,
the questions of how classifications are to be constructed and
even to what use they should be put are by no means settled. Carl
Linnaeus, in 1758, published Systema Naturae. This marks the beginning of the modern classification of plants
and animals. He devised practical techniques for the naming of
groups of organisms and their ranking and ordering. He developed
a system of binomial nomenclature - the scientific name of an
organism consists of a collective generic name and a specific
or species name. His techniques are basically intact today. Of
course, there are numerous philosophies and methods of classification
which are in use today which help add to the overall confusion
in the world of taxonomy. Linnaeus' great contribution was to
provide order in the method used in the classification of living
organisms.
Animals are classified according to the Linnaean system. This
consists of the following scheme, for example, in the classification
of several edible invertebrates. Each organism is uniquely identified using a combination of its genus and species
names. Species are grouped into genera,
families, orders, classes, and phyla, depending upon similarities
and inferred evolutionary relationships.
| American Lobster | Market Squid | Blue Mussel | Virginia Oyster | European Oyster | |
| Phylum | Arthropoda | Mollusca | Mollusca | Mollusca | Mollusca |
| Class | Malacostraca | Cephalopoda | Bivalvia | Bivalvia | Bivalvia |
| Order | Decapoda | Decapoda | Mytiloida | Pterioida | Pterioida |
| Family | Nephropidae | Loliginidae | Mytilidae | Ostreidae | Ostreidae |
| Genus | Homarus | Loligo | Mytilus | Crassostrea | Ostrea |
| Species | americanus | opalescens | edulis | virginica | edulis |
The names of genera are required by the rules of nomenclature
to be unique. But such rules do not apply to other taxons, even
though duplicate names should be avoided. For example, in the
table above, the order name Decapoda occurs in both arthropods
and molluscs, and the species name edulis occursin bivalves of different genera. Wouldn't it be nice if
duplicate names did not exist?
A category designates a given rank or level in a hierarchic classification.
Such terms as species, genus, family, and order designate categories.
A category is an abstract term. The organisms placed in these categories are concrete zoological objects.
Organisms, in turn, are not classified as individuals, but as
groups of organisms. Words like "bluebirds" or "thrushes" refer
to such groups. These are the concrete objects of classification.
Any such group of populations is called a taxon if it is considered
distinct to be worthy of being formally assigned to a definite
category in the hierarchic classification.
Categories, which designate rank in a hierarchy, and taxa (plural for taxon), which designates named groupings of organisms, are thus two very different kinds of phenomena.
Controversy usually reigns supreme over whether or not a particular
group is truly distinct enough to be a new taxon. If it is a new
taxon, taxonomists then determine which category the taxon will
be placed in.
Much of the task of the taxonomist consists of assigning taxa
to the appropriate categorical rank. The hierarchy of categories
that the classifying taxonomist recognizes is an attempt to express
similarity ("characters in common") and recency of common descent.
The most closely related species (occasionally subject to intense
debate) are combined into genera, groups of related genera into
subfamilies and families, these into orders, classes, and phyla.
In this procedure there is a drastic difference between the species
taxon and the higher taxa (genus on up to phylum). Higher taxa
are defined by intrinsic characters. For instance, the Class Aves
(birds) is the class of "feathered vertebrates". Any and all species
that satisfy the definition of "feathered vertebrates" belong
to the Class Aves.
Species Groups of actually or potentially interbreeding natural populations
which are reproductively isolated from other such groups. May or may not be morphologically distinct.
Genus The lowest higher category. A taxonomic category containing a
single species, or a monophyletic group of species, which is separated
from other taxa of the same rank by a decided gap (behavior, morphology,
or some other characteristics).
If these three species belong to the same genus, they are descended
from a common ancestor.
Family A taxonomic category including 1 genus or a group of genera of
common phylogenetic origin, which is separated from other families
by a decided gap.
Currently, there are about 26 known phyla, 80 classes, and 350
orders of extant animals. As one goes up the hierarchic scale from the species rank up to
phylum, each category becomes more inclusive.
Encourage students to be creative in their classification schemes!
When a species is collected and it is new to science, the most
important rules of ICZN cover:
1. Choice of a name - must be Latin, must not be already used,
and it must be in binomial form.
2. The name must be published in a well respected, preferably
international, scientific journal.
3. The publication must include a description of the new species.
4. Described species must be accompanied by a type or preferably
a set of type specimens which must be accessible to scientists
from the world over (i.e. the type specimens are placed into a
museum which allows access to all).
Terms, Laws, etc.
Law of Priority Except in extreme circumstances, a name proposed
first has precedence over all subsequently proposed names.
Type Specimens |
Type specimens are selected by the taxonomist to designate individuals
which typify the described species. Type specimens are placed
in museums for study by taxonomists. Often the type specimen does
not represent all the variation within a species (how could it!?).
The type specimen becomes the name bearer of the species. I have
listed a few different "types" in use by the taxonomist.
Holotype The single specimen indicated as "the type" by the original
author at time of publication of the original description.
Syntype One of two or more specimens cited by the author of a species
when no holotype was designated or it is any one of two or more
specimens originally designated as types.
Isotype A duplicate specimen of the holotype collected at the same place
and time as the holotype.
Neotype A specimen selected as type subsequent to the original description
in cases where the original types are known to be destroyed.
Finally- The Exercise |
We usually use about 15 different hardware items!
Divide into research teams. You have been handed a bag of various
fasteners (nails, staples, screws, etc.) As renowned taxonimists,
you are to develop a classification scheme that meets the established
rules of the Linnaean system. Be prepared to defend your classification
scheme orally. You will also write a one page essay on your classification
choices--what roles did form, function, derived characters, and
ancestral traits play in your classification scheme?
Tasks:
1. Make a phylogenetic chart of your classification scheme (as
shown on this handout) using the poster paper, tape, and objects.
Include all of the categories from phylum to species. What rationale
(s) did you use to for each category and what criteria did you
use to differentiate among categories? Did you rely more on "form"
or "function?" Or derived and ancestral traits? Provide descriptive
names for each category from phylum, class, order, family, genus
and species. Apply names that best describe each object and their
heirachical location in your classification scheme.
2. What are some of the difficulties and differences between classifying
inanimate objects and living organisms? Is it easier or more difficult
to classify living or inanimate objects? Why? If you knew nothing
about each object's function, would that have made a difference
in your classification scheme?
3-Does your classification scheme reflect the evolutionary relationships and phylogeny among taxa? Who evolved from whom? Which "body type" do you consider
to be the most primitive? The most advanced? Be sure to include
evolutionary relationships in your essay.
From Dr. Gary Anderson's vertebrate evolution page.
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