A Phylogenetic Analysis of the Caminalcules. III. Fossils and Classification

The consequences of introducing fossil species into a numerical taxonomic data set are examined, using the Caminalcules as an example. This group of “organisms” was generated artificially according to principles believed to resemble those operating in real organisms. Inclusion of fossils into the phenetic classification introduces some nonconvex taxa at higher phenetic levels, but unites phenetically homogeneous groups of mixed Recent and fossil composition. There is good correspondence of phenetics with phylogenetic sequences. The taxonomic relationships of the phenetic classification of Recent plus fossil forms can be explained by the amount of evolutionary change known to have occurred in given internodes. All but one of the mutually closest pairs in the phenogram are ancestor-descendant pairs. Gingerich's stratophenetic method yields a reasonably good estimated cladogram, but is misled by the occurrence of homoplasy in portions of the tree. Adding fossils improves estimates of the true cladogram based on the distance Wagner method but not estimates based on the Wagner parsimony algorithm. Estimated cladograms approach the true cladogram more closely than phenograms do, yet even the best estimate including the fossils has a strict consensus index no higher than 0.667. There are 10 characters that define genera. Their removal from the data base affects phenetic classifications slightly, cladistic classifications somewhat more. A cladistic classification of the Recent Caminalcules unnecessarily raises the ranks of some taxa. The less speciose and more symmetrical taxa emerge at lower taxonomic ranks than more speciose and asymmetrical taxa. Adding fossils to the Caminalcules requires a greater number of ranks for a cladistic than for a phenetic classification.