Recumbirostra 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, ...

tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct theraps ...

s which lived during the

Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...

and

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...

periods. They are thought to have had a

fossorial A fossorial () animal is one adapted to digging which lives primarily, but not solely, underground. Some examples are badgers, naked mole-rats, clams, meerkats, and mole salamanders, as well as many beetles, wasps, and bees. Prehistoric eviden ...

(burrowing) lifestyle and the group includes both short-bodied and long-bodied snake-like forms. At least one species, the molgophid ''

Nagini mazonense ''Nagini'' (from Sanskrit ''Nāga, Nāgá'', "snake") is an extinct genus of recumbirostran tetrapods from the middle Carboniferous of the Mazon Creek fossil beds, Illinois, United States. The type and only species, ''Nagini mazonense'', was nam ...

,'' lost its forelimbs entirely. It includes the families

Pantylidae Pantylidae is an extinct family of lepospondyl amphibians and often considered a sister-group to the family Tuditanidae. The family contains two genera '' Pantylus'' and '' Stegotretus'', while a third, ''Sparodus ''Sparodus'' is an extinc ...

Gymnarthridae Gymnarthridae is an extinct family of tuditanomorph microsaurs. Gymnarthrids are known from Europe and North America and existed from the Late Carboniferous through the Early Permian. Remains have been found from the Czech Republic, Nova Scotia, ...

Ostodolepidae Ostodolepidae, also spelled Ostodolepididae, is an extinct family of Early Permian microsaurs. They are unique among microsaurs in that they were large, reaching lengths of up to , terrestrial, and presumably fossorial. Ostodolepid remains have b ...

Rhynchonkidae ''Rhynchonkos'' is an extinct genus of microsaur. It is the only known member of the family Rhynchonkidae. Originally known as ''Goniorhynchus'', it was renamed in 1981 because the name had already been given to another genus; the family, likewis ...

and

Brachystelechidae Brachystelechidae is an extinct family of Early Permian microsaurs. The family was first named by Robert L. Carroll and Pamela Gaskill in 1978, with the only member being ''Brachystelechus fritschi''. ''Brachystelechus fritschi'' has since bee ...

, with additional families such as

Microbrachidae ''Microbrachis'' is an extinct genus of lepospondyl amphibian from the Carboniferous Kladno Formation of the Czech Republic. Description ''Microbrachis'' was an elongated, salamander-like creature, about long, with over 40 vertebrae ins ...

and

Molgophidae Lysorophia is an order of fossorial Carboniferous and Permian tetrapods within the Recumbirostra. Lysorophians resembled small snakes, as their bodies are extremely elongate. There is a single family, the Molgophidae (previously known as Lysoroph ...

being included by some authors. Recumbirostra was erected as a clade in 2007 to include many of the taxa traditionally grouped in "

Microsauria Microsauria ("small lizards") is an extinct, possibly polyphyletic order of tetrapods from the late Carboniferous and early Permian periods. It is the most diverse and species-rich group of lepospondyls. Recently, Microsauria has been considere ...

", which has since been shown to be a

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

polyphyletic A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of converg ...

grouping. Like other "microsaurs", the recumbirostrans have traditionally been considered to be members of the subclass

Lepospondyli Lepospondyli is a diverse taxon of early tetrapods. With the exception of one late-surviving lepospondyl from the Late Permian of Morocco (''Diplocaulus minumus''), lepospondyls lived from the Early Carboniferous ( Mississippian) to the Early Per ...

; however, many phylogenetic analyses conducted since the 2010s have recovered recumbirostrans as basal

sauropsid Sauropsida ("lizard faces") is a clade of amniotes, broadly equivalent to the class Reptilia. Sauropsida is the sister taxon to Synapsida, the other clade of amniotes which includes mammals as its only modern representatives. Although early syna ...

amniotes Amniotes are a clade of tetrapod vertebrates that comprises sauropsids (including all reptiles and birds, and extinct parareptiles and non-avian dinosaurs) and synapsids (including pelycosaurs and therapsids such as mammals). They are distingu ...

instead. Not all

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

analyses recognize Recumbirostra as a valid grouping. An alternative clade called

Tuditanomorpha Tuditanomorpha is a suborder of microsaur lepospondyls. Tuditanomorphs lived from the Late Carboniferous to the Early Permian and are known from North America and Europe. Tuditanomorphs have a similar pattern of bones in the skull roof. Tuditano ...

is occasionally supported and includes many of the same taxa.

Gallery

Phylogeny

Below is a

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...

showing the

relationships of recumbirostrans from Glienke (2012):

References

Pennsylvanian first appearances Cisuralian extinctions {{Permian-animal-stub