Form classification
Form classification is the classification of organisms based on their morphology, which does not necessarily reflect their biological relationships. Form classification, generally restricted to palaeontology, reflects uncertainty; the goal of science is to move "form taxa" to biological taxa whose affinity is known.[1]
Strictly defined, form taxonomy is restricted to fossils that preserve too few characters for a conclusive taxonomic definition or assessment of their biological affinity, but whose study is made easier if a binomial name is available by which to identify them.[2] The term "Form classification" is preferred to "Form taxonomy"; taxonomy suggests that the classification implies a biological affinity, whereas in fact form classification is about giving a name to a group of morphologically-similar organisms that may not be related.[1]
Parataxa
A "parataxon", or "sciotaxon" (Gr. "shadow taxon"), is a classification based on incomplete data: for instance, the larval stage of an organism that cannot be matched up with an adult. It reflects a paucity of data that makes biological classification impossible.[1] A sciotaxon is defined as a taxon thought to be equivalent to a true taxon (orthotaxon), but whose identity cannot be established because the two candidate taxa are preserved in different ways and thus cannot be compared directly.[1]
Organ taxa
In paleobotany, the term is occasionally substituted for the more correct term "organ taxon", meaning a group of fossils of a particular part of a plant, such as a leaf or seed, whose parent plant is not known because the fossils were preserved unattached to the parent plant.Attention: This template ({{ref doi}}) is deprecated. To cite the publication identified by doi:10.1046/j.0031-0239.2003.00337.x, please use {{cite journal}} with |doi=10.1046/j.0031-0239.2003.00337.x wrapped in <ref> instead. Names given to organ taxa may only be applied to the organs in question - and cannot be extended to the entire organism.[2] However, because a form genus is erected on morphological grounds (which do not change when its affinity is known), a form genus that can eventually be assigned to a higher biological group should not be renamed.[3]
Whilst organ genera can potentially be assigned to a family (even if the other parts of the plant are unknown), form genera usually cannot : although they may be referrable to higher categories (e.g. "Fungi" or "Animalia").[2]
The part of the plant is often, but not universally, indicated by the use of a suffix in the generic name:
- wood fossils may have generic names ending in -xylon
- leaf fossils generic names ending in -phyllum
- fruit fossils generic names ending in -carpon, -carpum or -carpus
- pollen fossils generic names ending in -pollis or -pollenoides.
Casual use
"Form taxon" can more casually be used to describe a wastebasket taxon: either a taxon that is not a natural (monophyletic) group but united by shared plesiomorphies, or a presumably artificial group of organisms whose true relationships are not known, being obscured by ecomorphological similarity.[verification needed] Well-known form taxa of this kind include "ducks", "fish", "reptiles" and "worms".[citation needed]
See also
Footnotes
- ^ a b c d Attention: This template ({{cite jstor}}) is deprecated. To cite the publication identified by jstor:1304949, please use {{cite journal}} with
|jstor=1304949instead. - ^ a b c Attention: This template ({{cite jstor}}) is deprecated. To cite the publication identified by jstor:1216676, please use {{cite journal}} with
|jstor=1216676instead. - ^ Attention: This template ({{cite jstor}}) is deprecated. To cite the publication identified by jstor:1218455, please use {{cite journal}} with
|jstor=1218455instead.