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 states 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 to be 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.
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, the wastebasket taxa 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 Thecodontia), or abandoned altogether (for example, Simia).
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.
Arctocyonidae (from Greek arktos kyôn, "bear/dog-like") has been defined as an extinct family of unspecialized, primitive mammals with more than 20 genera. Animals assigned to this family were most abundant during the Paleocene, but extant from the late Cretaceous to the early Eocene (66 to 50 million years ago).
Like most early mammals, their actual relationships are very difficult to resolve. No Paleocene fossil has been unambiguously assigned to any living order of placental mammals, and many genera resemble each other: generalized robust, not very agile animals with long tails and all-purpose chewing teeth, living in warm closed-canopy forests with many niches left vacant by the K-T extinction.Arctocyonids were early defined as a family of creodonts (early predators), then reassigned to the condylarths (primitive plant-eaters, now understood as a wastebasket taxon). More recently, these animals have been thought to be the ancestors of the orders Mesonychia and Cetartiodactyla, although some morphological studies have suggested that Arctocyonidae is also a wastebasket taxon for basal ungulates, and is in fact polyphyletic.
As of 2015, the largest cladistic study of Paleocene mammals to date supports the idea that the animals in this group are not related, with Arctocyon and Loxolophus sister to pantodonts+periptychids, Goniacodon and Eoconodon sister to carnivores+mesonychids, most other genera allied with creodonts and palaeoryctidans, and Protungulatum not a placental mammal at all. If this analysis holds true, then any "Arctocyonid" characteristics are the result of coincidence (selection by the observer of characteristics shared by many early Tertiary mammals) or convergence (similar habits in life).Baldwinonus
Baldwinonus is an extinct genus of basal synapsids from the Early Permian. The type species is Baldwinonus trux, named in 1940 from the Cutler Formation of New Mexico. A second species, Baldwinonus dunkardensis, was named in 1952 from Ohio. Baldwinonus was first classified in the family Eothyrididae, but the group has since been recognized as a wastebasket taxon for many early synapsids. More recently, Baldwinonus has been placed in the family Ophiacodontidae. Its phylogenetic relationship to other early synapsids remains poorly understood because it is only known from a few fragments of bone.Cetiosauridae
Cetiosauridae is a family of sauropod dinosaurs. While traditionally a wastebasket taxon containing various unrelated species, some recent studies have found that it may represent a natural clade. Additionally, at least one study has suggested that the mamenchisaurids may represent a sub-group of the cetiosaurids, which would be termed Mamenchisaurinae.Cichlasoma
Cichlasoma is a genus of fish in the cichlid family. The genus was previously very large (a wastebasket taxon), including cichlids from North America, including Central America, and South America.
Reclassification and subsequent splitting of the genus by Sven O. Kullander and other ichthyologists has resulted in removing many of the former species from the genus Cichlasoma. Several taxa now being placed within separate genera such as Amphilophus, Archocentrus, Herichthys, Heros, Nandopsis, Parachromis, Thorichthys, Vieja and a number of others.Dycheiidae
Dycheiidae is a wastebasket taxon containing problematic polyplacophora from Upper Cambrian strata in the USA.Eulipotyphla
Eulipotyphla ("truly fat and blind") is an order of mammals suggested by molecular methods of phylogenetic reconstruction, and includes the laurasiatherian members of the now-invalid polyphyletic order Lipotyphla, but not the afrotherian members (tenrecs and golden moles, now in their own order Afrosoricida). Lipotyphla in turn had been derived by removing a number of groups from Insectivora, the previously used wastebasket taxon.
Eulipotyphla comprises the hedgehogs and gymnures (family Erinaceidae, formerly also the order Erinaceomorpha), solenodons (family Solenodontidae), the desmans, moles, and shrew-like moles (family Talpidae) and true shrews (family Soricidae). True shrews, talpids and solenodons were formerly grouped in Soricomorpha; however, Soricomorpha has been found to be paraphyletic, since erinaceids are the sister group of shrews.Hyopsodontidae
Hyopsodontidae is an extinct family of unspecialized, primitive mammals from the order Condylarthra, living from the Paleocene to the Eocene in North America and Eurasia. Condylarthra is now thought to be a wastebasket taxon; hyopsodontids have occasionally been speculated to be related to Afrotheria, while the most recent consensus appears to be as part of Perissodactyla, and in particular closely related to horses.They were generally small insectivorous animals. The most common genus is Hyopsodus.
All of them were small ungulates, their size ranging from that of a squirrel to that of a weasel. Although much more herbivorous in their diet than the arctocyonids, and lacking their powerful canines, the hyopsodontids still had a generalized dentition, with a full set of incisors, canines, premolars, and molars. During the Paleocene in Europe, they reached a high diversity level, starting with Louisina and Monshyus in Hainin, Belgium, and following in the Cernaysian beds with Tricuspiodon, Paratricuspiodon, and Paschatherium.Mabuya
Mabuya is a genus of long-tailed skinks restricted to species from various Caribbean islands. They are primarily carnivorous, though many are omnivorous. The genus is viviparous, having a highly evolved placenta that resembles that of eutherian mammals. Formerly, many Old World species were placed here, as Mabuya was a kind of "wastebasket taxon". These Old World species are now placed in the genera Chioninia, Eutropis, and Trachylepis. Under the older classification, the New World species were referred to as "American mabuyas", and now include the genera Alinea, Aspronema, Brasiliscincus, Capitellum, Maracaiba, Marisora, Varzea, and Copeoglossum.
The ancestors of the genus are believed to have rafted across the Atlantic from Africa during the last 9 million years.Machairodus
Machairodus is a genus of large machairodontine saber-toothed cats that lived in Europe, Asia, Africa and North America from the late Miocene to the Middle Pleistocene. It is the animal from which the family Machairodontidae gets its name and has since become a wastebasket taxon over the years as many genera of sabertooth cat have been and are still occasionally lumped into it.Meridiungulata
Meridiungulata is an extinct clade with the rank of cohort or superorder, containing the South American ungulates Pyrotheria (possibly including Xenungulata), Astrapotheria, Notoungulata and Litopterna. It is not known if it is a natural group; it was erected to distinguish the ungulates of South America from other ungulates. Relationships between the orders inside Meridiungulata remain unresolved and it could well be a "wastebasket taxon". Most Meridiungulata died out following the invasion of South America by North American ungulates and predators during the Great American Interchange, but a few of the largest species of notoungulates and litopterns survived until the end-Pleistocene extinctions.Mesozoa
The Mesozoa (singular: mesozoan) are minuscule, worm-like parasites of marine invertebrates. Generally, these tiny, elusive creatures consist of a somatoderm (outer layer) of ciliated cells surrounding one or more reproductive cells. Decades ago, Mesozoa were classified as a phylum. Molecular phylogeny studies, however, have shown that the mysterious mesozoans are monophyletic, and emerged in the Lophotrochozoa as sister of the Rouphozoa.As a result of these recent findings in molecular biology, the label mesozoan is now often applied informally, rather than as a formal taxon. Some workers previously classified Mesozoa as the sole phylum of the lonely subkingdom Agnotozoa. Cavalier-Smith argued that at least some of the mesozoans are in fact protistans, not animals.In the 19th century, the Mesozoa were a wastebasket taxon for multicellular organisms which lacked the invaginating gastrula which was thought to define the Metazoa.Neosodon
Neosodon (meaning "new tooth") was a genus of sauropod dinosaur from the Late Tithonian-age Upper Jurassic Sables et Gres a Trigonia gibbosa of Départment du Pas-de-Calais, France. It has never been formally given a species name, but is often seen as N. praecursor, which actually comes from a different animal. Often in the past, it had been assigned to the wastebasket taxon Pelorosaurus, but restudy has suggested that it could be related to Turiasaurus, a roughly-contemporaneous giant Spanish sauropod.Oplosaurus
Oplosaurus (meaning "armed or weapon lizard" or "armoured lizard"; see below for discussion) was a genus of sauropod dinosaur from the Barremian-age Lower Cretaceous Wessex Formation of the Isle of Wight, England. It is known from a single tooth usually referred to the contemporaneous "wastebasket taxon" Pelorosaurus, although there is no solid evidence for this.Orthoceras
Orthoceras ("straight horn") is a genus of extinct nautiloid cephalopod restricted to Middle Ordovician-aged marine limestones of the Baltic States and Sweden. This genus is sometimes called Orthoceratites. Note it is sometimes misspelled as Orthocera, Orthocerus or Orthoceros (Sweet 1964:K222).
Orthoceras was formerly thought to have had a worldwide distribution due to the genus' use as a wastebasket taxon for numerous species of conical-shelled nautiloids throughout the Paleozoic and Triassic. Now, Orthoceras sensu stricto refers to O. regulare, of Ordovician-aged Baltic Sea limestones of Sweden and neighboring areas.These are slender, elongate shells with the middle of the body chamber transversely constricted, and a subcentral orthochoanitic siphuncle. The surface is ornamented by a network of fine lirae (Sweet 1964:K224). Many other very similar species are included under the genus Michelinoceras.Palaeoscolex
Palaeoscolex is the type genus of the Palaeoscolecid worms, and served as a wastebasket taxon. until its taxonomy was revised and many of its taxa assigned to Wronascolex.The type and only unequivocal species is P. piscatorum, known from mid-trunk segments.Phenacodontidae
Phenacodontidae is an extinct family of large herbivorous mammals traditionally placed in the “wastebasket taxon” Condylarthra, which may instead represent early-stage perissodactyls. They lived between the Paleocene and Eocene epochs (about 60–50 million years ago) and their fossil remains have been found in North America and Europe.Protorthoptera
The Protorthoptera are an extinct order of Palaeozoic insects, and represent a wastebasket taxon and paraphyletic assemblage of basal neoptera. They appear during the Middle Carboniferous (late Serpukhovian or early Bashkirian), making them among the earliest known winged insects in the fossil record. Pronotal lobes may be expanded to form a shield. The group includes the ancestors of all other polyneopterous insects.Tricholomataceae
The Tricholomataceae are a large family of mushrooms within the Agaricales. A classic "wastebasket taxon", the family is inclusive of any white-, yellow-, or pink-spored genera in the Agaricales not already classified as belonging to e.g. the Amanitaceae, Lepiotaceae, Hygrophoraceae, Pluteaceae, or Entolomataceae.
Some species of fungus-growing ants in the genus Apterostigma cultivate species of Tricholomataceae.The name derives from the Greek trichos (τριχος) meaning hair and loma (λωμα) meaning fringe or border, although not all members display this feature.Arnolds (1986) and Bas (1990) also place the genera of the Hygrophoraceae within this family, but this classification is not accepted by the majority of fungal taxonomists.Molecular phylogenetic analysis has greatly aided in the demarcation of clear monophyletic groups among the Tricholomataceae. So far, most of these groups have been defined cladistically rather than being defined as formal Linnean taxa, though there have been several cases in which older proposed segregates from the Tricholomataceae have been validated by evidence coming from molecular phylogenetics. As of 2006, validly published families segregated from the Tricholomataceae include the Hydnangiaceae, Lyophyllaceae, Marasmiaceae, Mycenaceae, Omphalotaceae, Physalacriaceae, and Pleurotaceae.
In 2014 a study recovers seven monophyletic genera within the Tricholomataceae; Leucopaxillus, Tricholoma, Pseudotricholoma stat. nov, Porpoloma s.str, Dennisiomyces, Corneriella gen.nov. and Albomagister gen. nov. The aim of the study was to delimit the highly polyphyletic Tricholomataceae, and identyfiy monophyletic groups within the Tricholomatoid clade, which includes the families Tricholimoaceae, Entolomataceae, and Lyophyllaceae. According to this study there have been several different ways of distributing Porpoloma, which is highly polyphyletic. This study suggests that the genus Porpoloma is distributed in four groups within the Trichlomatatic clade; Porpoloma s.str, Corneriella gen.nov. and Pseudotricholoma stat. nov. and Pogonoloma.
The name "Tricholomataceae" is nevertheless seen as having validity in describing Tricholoma and its close relatives, and whatever other genera can at some future point be described as part of a monophyletic family including Tricholoma. To that end, the International Botanical Congress has voted on two occasions (1988 and 2006) to conserve the name "Tricholomataceae" against competing names. This decision does not invalidate the use of segregate families from the Tricholomataceae, but simply validates the continued use of Tricholomataceae.The extinct genus Archaeomarasmius, described from Turonian-age New Jersey amber, is one of four known genera of Agaricales in the fossil record.Valenopsalis
Valenopsalis is an extinct mammal from the Paleocene of North America (more specifically, Puercan-aged deposits in Wyoming, Montana and Saskatchewan. Originally referred to the genus Catopsalis (C. joyneri), it has more recently been moved to its own genus as the former was understood to be a wastebasket taxon. It is currently considered to be the most basal representative of Taeniolabidoidea.