Are fungi closer to animals than plants? What does a phylogenetic tree show? What is the role of a cladogram? Why are dolphins considered Ungulates? What is the "missing link"? Are birds mammals?
Why, or why not? What is synapomorphy? However, the rigor cladistics introduces to systematics is useful in getting traditional systematists to look at their subjective classifications in a new light. On the diagram below, shared derived characters are indicated as hauchers across the lines. The mammal clade is united by fur, the lizard, pigeon, mouse-chimp clade is united by claws or nails, etc.
The example used above, if treated cladistically, would produce a very different classification! Note that crocodiles have more in common in a cladistic sense with birds than they do with other reptiles. Birds and crocs form a clade, or monophyletic group united by shared derived characters not present in the other groups. If we construct a Linnean group from this cladogram, we have a class of birds and crocodiles, a second class of lizards, snakes, and turtles, and a third class of mammals.
One of the more interesting applications of cladistics is to the question of the pandas. The giant panda was once thought to be a bear, but later its racoon-like characters caused it to be placed closer to racoons. The red lesser panda lives in the same areas of China as the giant panda, but has a far greater similarity with racoons. DNA hybridization studies suggest the giant panda is in the bear clade, while the red panda is in the racoon clade.
Both share a common ancestry, as indicated by shared derived characters, followed by convergent evolution of other characters. The diagram above indicates this divergence from common ancestry, and even attempts to show the time of that divergence. Phenetics is a process by which taxa are clustered together based on the number of their similarities or differences, depending on the numerical coefficient employed. Traits are measured and either converted into integers or input directly as numerical data.
Theses data are then mathematically processed using an algorithm that generates a similarity or distance as the case may be matrix. Various graphical representations of this matrix include a phenogram, and principal coordinate plot. Phenetic classifications are plagued by problems of convergence and parallelism, but are useful in their attempt to objectify the classification process. My previous work on triprojectate pollen employed phenetics to deal with a wide array of subjective ratios or other classification methods.
Convergence was a given with this group of fossil pollen produced by one or more groups of unknown extinct plants. Since monophylesis could not be established for the entire group, phenetics was use to help delineate possible monophyletic groups for eventual cladistic study. Monera are the only kingdom composed of prokaryotic organisms, they have a cell wall, and lack both membrane-bound organelles and multicellular forms.
The Archaebacteria, the most ancient of this kingdom, are so different that they may belong to a separate kingdom. Other groups of Monera include the cyanobacteria autotrophic and eubacteria heterotrophic. Phylogenetic classification has replaced the traditional classification in most of the scientific community and in secondary education in France. Dans la rubrique Definitions. Make a donation. Membership form. Write us! Please leave this field empty:. Traditional taxonomic classification or phylogenetics?
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