A Guide to the Dinosaurs of Colorado
On Dinosaur Classification
On Scientific Names
The Basics of Taxonomy
An Introduction to Cladistcs
Taxonomy of the Dinosaurs of Colorado
Cladogram of the Dinosaurs of Colorado
About the Dinosaurs of Colorado
Geological
Time Chart
An Introduction to Cladistics
There are two distinct taxonomic systems currently in vogue among professional zoologists today. The traditional, or Linnaean, taxonomy is still largely in favor among field workers, conservationists, and husbandry people. The alternative, Cladistic taxonomy, is overwhelmingly supported by evolutionary biologists, and by many paleontologists. (The Linaean taxonomic system is described in "The Basics of Taxonomy".)A clade is just a fancy word for group, but in cladistic taxonomy, it has a very precise definition. Any clade can be defined as two member species (or any other taxonomic group) and all the descendants of their nearest common ancestor. Depicted graphically as a cladogram, relationships are shown on a binary tree, where every fork has exactly two branches, with each clade represented by a fork. No matter what the relationship is between the groups depicted in a cladogram, there will always be one less clade than the number of groups. Thus, any cladogram depicting eight taxonomic groups will always contain seven clades, regardless of their arrangement, as shown:
|
|
|
|
Cladogram 1. Groups G and H are most closely related, while group A is the most distant. Clades are represented by numbers 1 through 7. |
Cladogram 2. Groups A and B are more closely related to each other than to any other group, as are C and D, E and F, and G and H. Clade 4 is more closely related to 5, and clade 6 is more closely related to 7. |
Some cladograms are depicted graphically, like the illustrations above, but when a large number of clades are to be depicted, nothing smaller than a wall chart would do. For the printed page or the computer screen, a more concise representation has been developed. Using a fixed-width font, the information in the second cladogram would be represented thus:
--Clade 1
|--Clade 2
| |--Clade 4
| | |-->Group A
| | `-->Group B
| `--Clade 5
| |-->Group C
| `-->Group D
`--Clade 3
|--Clade 6
| |-->Group E
| `-->Group F
`--Clade 7
|-->Group G
`-->Group H
With two to ten million species of plants, animals, and micro-organisms that are known or presumed to exist, assigning unique Latin names to each genus and every clade becomes a daunting task. Even using latinizations of Greek, English, and now even Chinese words, scientific names are becoming longer and harder to remember. For greater brevity and ease of memorization, traditional Linnaean taxonomy is still preferred by many scientists.
Site designed and hosted by: WebSpinners (info@webspinners.com)