Cladistics is a recently developed methodology, with its adherents and detractors, and many disagreements over how it should be practiced. (Walking dinosaur costume) I follow a pragmatic approach, one that falls back on conunon sense when all else fails. To construct a cladistic “family tree,” a cladograrn, one starts with an outgroup-this is the group or species of primitive forms that the species being looked at will be compared to. (Realistic dinosaur costume)The reader is cautioned that the terms primitive and advonced are often loaded terms in lay use, with primitive considered inferior to advanced. In phylogenetic use, they do not carry the same connotation. Primitive or archaic is the initial or basal condition, advanced is the subsequent or derived condition. Advanced mcy be more sophisticated and effective than primitive, or it may simply be different. Lizards, for example, are more “primitive” than mammals; but lizards have been increasingly successful over the last hundred million years, showing they are effective animals well adapted to the conditions they live in.
Having a basal outgroup, one then looks for shared-derived characters among the rest of the groups under investigation. Animatronic dinosaur Shared-derived characters are simply those that differ from the outgroup’s and are shared by two or more species. Quality is important as well as quantity, for the more complex an adaptation, the less likety it is to have developed more than once. After tabulating the shared-derived characters, the possibilities of convergence and parallelism are assessed. There is no simple formula for this, and a good deal of judgment is involved. Bias in the characters chosen and the tremendous gaps in our knowledge make things worse. Indeed, some recent studies have come up with bizarre and misleading results becasue they looked at too few characters. So, the more data the better. Yet the greater the number of species and characters looked at, the less the human mind is able to take it all in and weigh the various factors. Even computers are strained when assessing a modest number of characters and taxa. Some of us paleontologists delight in accumulating and assessing vast numbers of characters and trying to sort them out into a logical family tree. Detailing all this minutiae would take up much of the book, so only the telling highlights are explored here.