Wastebasket taxon
Wastebasket taxon (also called a wastebin taxon, dustbin taxon or catch-all taxon) is a term used by some taxonomists to refer to a taxon that has the sole purpose of classifying organisms that do not fit anywhere else. They are typically defined by either their designated members' often superficial similarity to each other, or their "lack" of one or more distinct character stats or by their "not" belonging to one or more other taxa. Wastebasket taxa are by definition either paraphyletic or polyphyletic, and are therefore not considered valid taxa under strict cladistic rules of taxonomy. The  name of a wastebasket taxon may in some cases be retained as the designation of an evolutionary grade, however. Wastebasket taxa in science. Fossil groups that are poorly known due to fragmentary remains are sometimes grouped together on gross morphology or stratigraphy, only later to be found to be wastebasket taxa, such as the crocodile-like Triassic group Rauisuchia. One of the roles of taxonomists is to identify wastebasket taxa and reclassify the content into more natural units. Sometimes, during taxonomic revisions, a wastebasket taxon can be salvaged after doing thorough research on its members, and then imposing tighter restrictions  on what continues to be included. Such techniques "saved" Carnosauria and "Megalosaurus". Other times, the taxonomic name contains too much unrelated "baggage" to be successfully salvaged. As such, it is usually dumped in favour of a new, more restrictive name (for example, Rhynchocephalia), or abandoned altogether (for example, "Simia"). Related concepts. A related concept is that of form taxon, "wastebasket" groupings that are united by gross morphology. This is often result of a common mode of life, often one that is generalist, leading to generally similar body shapes by convergent evolution. The term wastebasket taxon is sometimes employed in a  derogatory fashion to refer to an evolutionary grade taxon.