cladistics, trees and evolutionary inference

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A few thoughts in relation to the cladistics discussion, and Norm's latest 
missive in particular:

Although it seems very likely that the inclusion of living taxa in 
vertebrate phylogenetic analyses was a driving force behind the 
acceptance of cladistics in this field, cladistic analysis was also 
quickly applied to wholly or predominantly palaeontological problems (see 
for example Andrews 1973, in "Interrelationships of Fishes"). Probably the 
main reason for the impact of cladistics on vertebrate palaeontology was 
the nature of the vertebrate skeleton: a complex structure composed of 
numerous different, easily characterisable elements. Vertebrate skeletal 
material lends itself quite naturally to interpretation in terms of 
discrete characters, which can be polarised with relative ease. A less 
complex and less "atomised" skeletal anatomy (mollusc shells come to mind) 
may be more difficult to interpret in this way. Another factor was no 
doubt the incomplete fossil record and poor stratigraphic resolution of 
most vertebrate groups, which reduced the temptation to use stratophenetic 
approaches.

As for the uses of phylogeny, I basically agree with Norm and would 
thoroughly recommend Harvey & Pagel as a sourcebook for ideas and 
approaches. An interesting illustration of how evolutionary phylogenetics 
is developing is given by the early history of the lungfishes, a group 
which seems to show strong directional evolutionary "trends". The 
relationship between phylogeny, character distribution and evolution in 
the lungfishes has been tackled by Bemis (1984: Palaeobiology 10, 293-
307) and Long (1993: Mem. Ass. Australas. Palaeontols. 15, 199-209). 
However, some of Bemis' assumptions in particular are not very 
rigorously framed. I examine the problems in some detail an a 
forthcoming paper (Ahlberg & Trewin, in press: The postcranial skeleton 
of the Middle Devonian lungfish Dipterus valenciennesi. Trans. R. Soc. 
Edinb., Earth Sci.) which should be coming out during next spring. If 
anybody is interested I can run off a few copies of the discussion 
section from the manuscript and send them out.


Per Erik Ahlberg
Senior Research Fellow
Department of Palaeontology
The Natural History Museum
Cromwell Road, London SW7 5BD, UK
E-MAIL ADDRESS: pea@nhm.ac.uk