Cladograms - can't get enough of them

Agneta Guillemot Agneta.Guillemot at historia.umu.se
Tue Jun 20 18:30:55 EST 1995


When you start your studies in biology the first thing you  
run into is almost certainly a course which deals with the organism  
world as a whole. You are taught methods of recognising the most  
common of the living phyla in the animal kingdom. And you are  
taught a branching tree. Oh, those branching trees are everywhere  
in every textbook, with dotted lines and questionmarks, branches  
that end and start nowhere, but where is the analysis? I want to  
know some hard facts. 
  
I'm interested in knowing if there exists a complete cladogram  
over all extinct and extant phyla of the whole living world. That  
means including viruses, prokaryotes, eukaryotes, living or dead.  
If it exists, where can a find it? Who is the author(s). If it doesn't  
exist, I'm interested in finding one over all the animal phyla. I'm  
also interested in finding cladograms over all extant and extinct  
orders of chordates, and a cladogram over all extant and extinct  
families of birds. Maybee I'm not realistic about the progress  
cladists have made in classifying these taxa, but I hope somebody  
has made an attempt to clarify the evolutionary position of at least  
the animal phyla. It's so frustrating not to find any litterature  
where the positions of for example Tardigrades, Loriciferans or  
Ctenophores are explained satisfactorialy, or even chordates or  
molluscs. 
 
I strongly belive in cladistics as the only real way of determining  
the relationship of organisms. I do this because the theory behind  
the cladistic methodology is so strongly connected to how we  
believe that evolution happens, i.e. that two or more species when  
separating from one species inherits a set of unik charachters from  
it's most closest predecessor. If you find those characters you can  
detemine who is related to who, from the level of species, or  
subspecies, up to kingdom. I also believe that every stable heritable  
charachter is valid to use in a cladistic analysis, not only  
morphology. That is data from genetics, molecular biology,  
morfogenesis, behavior etc etc. You need only to follow the  
cladistical methodology. Indeed I belive that there will take place a  
second revolution in molecular systematics when you begin to  
apply cladistical methodology to it, instead of general likeness that  
has up to now been  the prevailing criteria for relationship between  
animals in molecular systematics. It's undoubtedly a field that will  
yield an enormous amount of new data in the coming years. I can  
only hope that the scientists are able to correctely interpret the new  
data.  
 
 
Ludvig Mortberg




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