''Lethiscus'' is the earliest known representative of the

Aistopoda Aistopoda (Greek for " avingnot-visible feet") is an order of highly specialised snake-like stegocephalians known from the Carboniferous and Early Permian of Europe and North America, ranging from tiny forms only , to nearly in length. They fi ...

, a group of very specialised snake-like

tetrapodomorph Tetrapodomorpha (also known as Choanata) is a clade of vertebrates consisting of tetrapods (four-limbed vertebrates) and their closest sarcopterygian relatives that are more closely related to living tetrapods than to living lungfish. Advanced for ...

s known from the early

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 ...

( Mississippian). ''Lethiscus'' is known from only a single specimen from the Holkerian Stage (Middle

Viséan The Visean, Viséan or Visian is an age in the ICS geologic timescale or a stage in the stratigraphic column. It is the second stage of the Mississippian, the lower subsystem of the Carboniferous. The Visean lasted from to Ma. It follows ...

) of the Early

(Middle Mississippian) of

Scotland Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the United Kingdom's land area, consisting of the northern part of the island of Great Britain and more than 790 adjac ...

, and is one of the oldest known post Devonian tetrapods. Despite its very early date, it was already a highly advanced animal. The skull is specialised and light, very like that of ''

Ophiderpeton ''Ophiderpeton'' (from , 'snake' and 'creeper') is an extinct genus of aistopod tetrapodomorphs from the early Carboniferous to the early Permian. Remains of this genus are widespread and were found in Ohio, United States, Ireland, and the Cz ...

'', with the

orbits In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an physical body, object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an satellite, artificia ...

, far forward, and the cheek region unossified (lacking bone). There are approximately 30 closely spaced teeth on the

maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...

and

dentary In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone ...

, and a sutural pattern of the skull closely resembles that of the

Late Carboniferous Late or LATE may refer to: Everyday usage * Tardy, or late, not being on time * Late (or the late) may refer to a person who is dead Music * Late (The 77s album), ''Late'' (The 77s album), 2000 * Late (Alvin Batiste album), 1993 * Late!, a pseudo ...

aïstopod ''

Oestocephalus ''Oestocephalus'' is an extinct genus of Aïstopoda, aïstopod tetrapodomorphs that lived during the Carboniferous period. Fossils have been found in the Czech Republic, and in Ohio and Illinois in the United States. It is the type genus of the f ...

''. There is no trace of limbs. However, unlike later members of the aïstopod lineage, the

vertebra Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spina ...

e still possess intercentra, and the pleurocentra are large. ''Lethiscus'' is the only representative of the family Lethiscidae. Owing to its early date, it has since its discovery been considered ancestral to later aïstopods, and more recent cladistic research (Anderson ''et al.'' 2003) confirms its position as the most basal (primitive) aistopod. A 2017 cladistic analysis incorporated new data on ''Lethiscus'' found all aïstopods, including ''Lethiscus'', to be stem-tetrapods, rendering

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 ...

polyphyletic.Jason D. Pardo, Matt Szostakiwskyj, Per E. Ahlberg & Jason S. Anderson (2017) ''Hidden morphological diversity among early tetrapods''. Nature (advance online publication)

References

* * Carroll, R.L (1988), ''Vertebrate Paleontology and Evolution'', WH Freeman & Co. pp. 176–7 *

Footnotes

External links

Aistopoda - phylogeny
{{Taxonbar, from=Q1619492 Aistopoda Mississippian sarcopterygians of Europe Fossil taxa described in 1982