''Lethiscus'' is the earliest known representative of the Aistopoda, a group of very specialised snake-like amphibians known from the early Carboniferous ( Mississippian). ''Lethiscus'' is known from only a single specimen from the

Holkerian The Holkerian is a sub-stage of the Viséan stage of the International Commission on Stratigraphy (ICS) geological timescale. It is one of five sub-stages commonly used in the Viséan stage within stratigraphy by British, Irish and other geologists ...

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 follow ...

) of the Early Carboniferous (Middle Mississippian) of

Scotland Scotland (, ) is a Countries of the United Kingdom, country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a Anglo-Scottish border, border with England to the southeast ...

, 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'', with the

orbits In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

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

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates 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. T ...

and

dentary In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

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

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

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...

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 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 Pe ...

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
Carboniferous amphibians of Europe Aistopods Fossil taxa described in 1982 {{carboniferous-animal-stub