Olsoniformes is a

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

dissorophoid Dissorophoideans are a clade of medium-sized, temnospondyl amphibians that appeared during the Moscovian in Euramerica, and continued through to the Late Permian and the Early Triassic of Gondwana. They are distinguished by various details of the ...

temnospondyl Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order (biology), order of small to giant tetrapods—often considered Labyrinthodontia, primitive amphi ...

s. It includes the families

Dissorophidae Dissorophidae is an extinct family of medium-sized, temnospondyl amphibians that flourished during the late Carboniferous and early Permian periods. The clade is known almost exclusively from North America. History of study Dissorophidae is a ...

and

Trematopidae Trematopidae is a family of dissorophoid temnospondyl spanning the late Carboniferous to the early Permian. Together with Dissorophidae, the family forms Olsoniformes, a clade comprising the medium-large terrestrial dissorophoids. Trematopids a ...

. Most members of the clade were highly adapted to a terrestrial lifestyle. The clade was named in 2008 and is defined as the least inclusive clade containing ''Dissorophus multicinctus'' (a dissorophid) and ''Acheloma cumminsi'' (a trematopid) but not ''Amphibamus grandiceps, Micromelerpeton credneri,'' and ''Apateon pedestris''. Olsoniforms share various features such as a stout and low ilium and a thin cultriform process. Trematopids are known from the

Late Carboniferous Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...

and the

Early Permian 01 or '01 may refer to: * The year 2001, or any year ending with 01 * The month of January * 1 (number) Music * '01 (Richard Müller album), 01'' (Richard Müller album), 2001 * 01 (Son of Dave album), ''01'' (Son of Dave album), 2000 * 01 (Urban ...

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

and across much of

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

, while dissorophids are primarily found in

deposits in the central

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

, extending into the Middle-Late Permian in Eurasia. Below is a cladogram from Schoch (2018) showing the phylogenetic position of Olsoniformes within the Dissorophoidea:

References

Carboniferous temnospondyls Permian temnospondyls Fossil taxa described in 2008 Olsoniforms {{temnospondyli-stub