graphic © Darren Abbey
Illustration: it used to be thought (in Victorian times) that all pachydermous (large stocky hairless thick-skinned herbivores) mammals - e.g. rhinos, hippos, and elephants - were descended from a single large ancestor. It is now known that each of these animals evolved from a seperate small ancestor, and the common ancestor of all of them was small and slightly built, with presumably thin skin and fur
Another Illustration: Some cladists (e.g. Lovtrup and Gardiner) have argued that because warm-blooded birds and mammals share a number of metabolic and anatomical features in common they must have descended from a single warm-blooded Most Recent Common Ancestor and thus constuitute the clade Haemothermia. It is now known that endothermy (warm-bloddedness) evolved independently in each group.
Polyphyletic taxa are considered invalid or unnatural groupings, and are not accepted in either the Linnean/Evolutionary or the Cladistics taxonomies. Metaphysically-speaking they are still valid, in that the members of the taxon, while not phylogenetically related (i.e. they do not share a Common Ancestor with the same chracteristics) nevertheless resonate to the same morphic field. The Polyphylertic taxon is therefore morphogentically valid, but not biologically or scientifically valid.
Examples: Pachyderma, Haemothermia, Algae, Arthropoda,
graphic (above) from
page historypage uploaded 13 November 1998