Reconstruction by Smokeybjb.
When: Late Permian (~275 - 270 million years ago)
Where: Oklahoma, USA
What: Rhynchonkos is a very rare amphibian that lived in the swamp land covering what is now Oklahoma in the Permian. It was about 4.5 inches (~11 cm) long, not counting the tail, with an extremely elongated body and tiny tiny limbs. The elongation of its body compared to other amphibians was accomplished via replication of vertebrae, not elongation of each individual bone. Rhynchonkos had at least 36 pre-sacral (before the hips) vertebrae. Its mouth was full of rows of tiny teeth, and it is likely that it ate insects and small fish in its swampy home. Older literature about this animal refers to it as Goniorhynchus rather than its current name. This change is due to the fact that the fossil taxon was named in 1970, however, a moth was given the name Goniorhynchus in 1896. Stupid insects. At least it wasn’t a beetle this time! The name Rhynchonkos was applied in 1981.
The phylogentic relationships of Rhynchonkos are fairly uncertain. For some time it was held as a close relative of modern caecilians (a group of limbless amphibians), but later fossil finds have cast doubt upon this affiliation. Within other fossil ‘amphbians’ Rhynchonkos has been placed in Lepospondyli (along with our friend Diplocaulus). This group as a whole has a much debated relationship with living amphibians. Some studies have them having nothing to do with living amphibians (lissamphibians), where as others link specific taxa with certain groups of living amphibians. Such as the now disputed Rhynchonkos - caecilian link. It may seem obvious to link this almost limbless fossil with the limbless amphibians, but amphibians (and lizards too!) seem to like to lose their limbs at the drop of a hat. It is very common in swimming and burrowing forms.