| Lethiscus Temporal range: EarlyCarboniferous | |
|---|---|
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Sarcopterygii |
| Clade: | Tetrapodomorpha |
| Order: | †Aistopoda |
| Family: | †Lethiscidae Wellstead, 1982 |
| Genus: | †Lethiscus Wellstead, 1982 |
| Species: | †L. stocki |
| Binomial name | |
| †Lethiscus stocki Wellstead, 1982 | |
Lethiscus is the earliest known representative of theAistopoda, a group of very specialised snake-liketetrapodomorphs known from the earlyCarboniferous (Mississippian).
Lethiscus is known from only a single specimen from theHolkerian Stage (MiddleViséan) of the EarlyCarboniferous (MiddleMississippian) ofScotland, 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 ofOphiderpeton, with theorbits, far forward, and the cheek region unossified (lacking bone). There are approximately 30 closely spaced teeth on themaxilla anddentary, and a sutural pattern of the skull closely resembles that of theLate Carboniferous aïstopodOestocephalus.
There is no trace of limbs. However, unlike later members of the aïstopod lineage, thevertebrae still possessintercentra, and thepleurocentra are large.
Lethiscus is the only representative of the familyLethiscidae. Owing to its early date, it has since its discovery been considered ancestral to later aïstopods, and more recent cladistic research (Andersonet al. 2003) confirms its position as the most basal (primitive) aistopod. A 2017 cladistic analysis incorporated new data onLethiscus found all aïstopods, includingLethiscus, to be stem-tetrapods, renderingLepospondyli polyphyletic.[1]
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