Form classification

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Vendozoan Charnia
. The actual nature or phylogeny of the Vendozoan is not known, leading to form taxa only

Form classification is the classification of organisms based on their

palaeontology, reflects uncertainty; the goal of science is to move "form taxa" to biological taxa whose affinity is known.[1]

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 form classification is about giving a name to a group of morphologically-similar organisms that may not be related.[1]

A "parataxon" (not to be confused with parataxonomy), 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]

Examples

In zoology

Form taxa are groupings that are based on common overall forms. Early attempts at classification of

Neornithes
but are nowadays recognized to unite a number of unrelated early neornithine lineages, several of which probably later gave rise to the "seabird" form taxon of today.

Fossil eggs are classified according to the parataxonomic system called

Veterovata. There are three broad categories in the scheme, on the pattern of organismal phylogenetic classification, called oofamilies, oogenera and oospecies (collectively known as ootaxa). The names of oogenera and oofamilies conventionally contain the root "oolithus" meaning "stone egg", but this rule is not always followed. They are divided up into several basic types: Testudoid, Geckoid, Crocodiloid, Dinosauroid-spherulitic, Dinosauroid-prismatic, and Ornithoid.[4]

In botany

In

codes of nomenclature, "form genera" and "organ genera", to mean groups 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.[5][6] A later term "morphotaxa" also allows for differences in preservational state. These three terms have been replaced as of 2011 by provisions for "fossil-taxa" that are more similar to the provisions for other types of plants.[7][8]

Names given to organ genera could only be applied to the organs in question, and could not be extended to the entire organism.

priority with any names for the same organism that are based on a non-fossil type.[7]

The part of the plant was often, but not universally, indicated by the use of a

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

ecomorphological similarity.[verification needed] Well-known form taxa of this kind include "ducks", "fish", and "worms".[citation needed
]

See also

Footnotes