Recumbirostra is a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...

s which lived during the

Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...

and

Permian The Permian ( ) is a geologic period and System (stratigraphy), 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 251.902 Mya. It is the s ...

periods. They are thought to have had a

fossorial A fossorial animal () is one that is adapted to digging and which lives primarily (but not solely) underground. Examples of fossorial vertebrates are Mole (animal), moles, badgers, naked mole-rats, meerkats, armadillos, wombats, and mole salamand ...

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

Nagini mazonense ''Nagini'' (from Sanskrit '' 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 named by ...

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

Pantylidae Pantylidae is an extinct family of tetrapods of the group Recumbirostra. It also often considered a phylogeny, sister-group to the family Tuditanidae. The family contains two genera ''Pantylus'' and ''Stegotretus'', while a third, ''Sparodus'', ...

Gymnarthridae Gymnarthridae is an extinct family of the group Recumbirostra. 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, I ...

Ostodolepidae Ostodolepidae, also spelled Ostodolepididae, is an extinct family of Early Permian tetrapods. Initially they were considered microsaurs, but later were assigned to the group Recumbirostra. Ostodolepids were relatively large, reaching lengths of ...

, Rhynchonkidae and

Brachystelechidae Brachystelechidae is an extinct family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social o ...

, with additional families such as Microbrachidae and Molgophidae being included by some authors. Brachystelechidae and Molgophidae have also been grouped together in the suggested clade Chthonosauria. Recumbirostra was erected as a clade in 2007 to include many of the taxa traditionally grouped in "

Microsauria Microsauria is an Extinction, extinct, possibly polyphyletic Order (biology), 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 ...

", which has since been shown to be a

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

polyphyletic A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...

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

Lepospondyli Lepospondyli is a diverse clade of early tetrapods. With the exception of one late-surviving lepospondyl from the Late Permian of Morocco ('' Diplocaulus minimus''), lepospondyls lived from the Visean stage of the Early Carboniferous to the Ea ...

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

sauropsid Sauropsida ( Greek for "lizard faces") is a clade of amniotes, broadly equivalent to the class Reptilia, though typically used in a broader sense to also include extinct stem-group relatives of modern reptiles and birds (which, as theropod dino ...

(reptilian)

amniotes Amniotes are tetrapod vertebrate animals belonging to the clade Amniota, a large group that comprises the vast majority of living terrestrial and semiaquatic vertebrates. Amniotes evolved from amphibious stem tetrapod ancestors during the ...

instead. However, the placement of recumbirostrans as reptiles has been challenged by other authors, who have recovered them as stem-amniotes instead, and contended that the shared characters between recumbirostrans and reptiles are convergent, or the result of incorrect character encoding. Not all

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

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

Tuditanomorpha Tuditanomorpha is a suborder of microsaur tetrapods. 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. Tuditanomorp ...

is occasionally supported and includes many of the same taxa. Furthermore, the taxa that are often considered to be recumbirostrans have been found among amphibians (and not as a distinct clade) in some analyses.

Classification

Taxonomy

* ''

Altenglanerpeton ''Altenglanerpeton'' is an extinct genus of microsaur tetrapod from the Late Carboniferous or Early Permian of Germany. ''Altenglanerpeton'' was named in 2012 after the Altenglan Formation in which it was found. The type and only species is ''A. ...

'' * ''

Sparodus ''Sparodus'' is an extinct genus of microsaur within the family Gymnarthridae Gymnarthridae is an extinct family of the group Recumbirostra. Gymnarthrids are known from Europe and North America and existed from the Late Carboniferous through t ...

'' * '' Steenerpeton?'' * ''

Trihecaton ''Trihecaton'' is an extinct genus of microsaur from the Late Pennsylvanian of Colorado. Known from a single species, ''Trihecaton howardinus'', this genus is distinctive compared to other microsaurs due to possessing a number of plesiomorphic ( ...

''? *

Hapsidopareiidae Hapsidopareiidae is an extinct family of microsaurs. Hapsidopareiids are known from the Early Permian of the United States and possibly Germany and the Czech Republic. Hapsidopareiids are characterized by a large temporal embayment near the chee ...

* Microbrachidae? *

Odonterpetidae Recumbirostra is a clade of tetrapods which lived during the Carboniferous and Permian periods. They are thought to have had a fossorial (burrowing) lifestyle and the group includes both short-bodied and long-bodied snake-like forms. At least one ...

**'' Odonterpeton'' **'' Joermungandr'' * Chthonosauria **

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

? * Nastrondormes **

** Rhynchonkidae / Goniorhynchidae *** '' Aletrimyti'' *** '' Dvellecanus'' *** ''

Rhynchonkos ''Rhynchonkos'' is an extinct genus of rhynchonkid microsaur. Originally known as ''Goniorhynchus'', it was renamed in 1981 because the name had already been given to another genus; the family, likewise, was originally named Goniorhynchidae but ...

'' **

Phylogeny

Below is a

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

showing the

relationships of recumbirostrans from Glienke (2012):

Gallery

References

{{Taxonbar, from=Q7303248 Microsauria Pennsylvanian first appearances Cisuralian extinctions