Palaeos Palaeos Evolutionary systematics
and systematics
Evolutionary systematics

Evolutionary systematics

Phylogeny through deep time

Evolution of the hoofed mammals

A "romerogram" (spindle diagram), showing the evolution of hoofed mammals plotting diversity (horizontal axis) against time (vertical axis), and showing the phylogentic divergence of new groups as new bubbles or balloons which increase or decrease in diversity of individuals and species through time. Diagram from Trees, Bubbles, and Hooves.

Evolutionary systematics combines Linnaean classification with ancestor-descendent relationships (phylogeny, evolution) through deep time, emphasising the stratigraphic sequence in the fossil record. Emphasis is placed on supra-specific taxa, such as orders or classes, rather than on species, and paleontology is as important if not more important than neontology. The emphasis is equally on "horizontal" similarity and "vertical" phylogeny. For this reason, generalised ancestral groups are frequently referred to, such as the Condylartha, shown in the above diagram, the Cotylosauria, and Thecodontia, all of which are considered stem groups from which later groups radiated.

Evolutionary systematic bubble or spindle diagrams are very common in paleontology books from the 1930s to the 70s, this type of diagram being being popularised (but not invented) by Aldfred Sherwood Romer (hence the name, "romerogram"). Their last serious use in a vertebrate paleontology textbook seems to be Carroll, 1988, although Benton 2004 has revised them in modified form. One big difference between evolutionary systematic trees and cladistic trees is that the former include ancestral groups, as mentioned above, whereas such taxa, being paraphyletic, are forbidden in cladistic methodology, as they are defined only by shared primitive characteristics. The latter is concerned instead with sister relationships of individual species, or even, in the case of fossils, individual specimens. However, rather than being a replacement for evolutionary systematics, cladistics is a totally different system, with different methodology and taxonomic philosophy. MAK111014

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