Caerorhachis (meaning "suitable spine" inGreek) is an extinctgenus of earlytetrapod from theEarly Carboniferous ofScotland, probably from theSerpukhovian stage.[1] Its placement within Tetrapoda is uncertain, but it is generally regarded as a primitive member of the group. Thetype speciesC. bairdi was named in 1977.[2]
Caerorhachis has usually been placed as abasalanthracosaur or a close relative of anthracosaurs. In this classification,Caerorhachis is a close ancestor ofamniotes, or tetrapods that lay eggs on land.Caerorhachis has also been classified as thesister taxon oftemnospondyls, a large group of extinctamphibians, based on the presence of several primitive traits.[3] In fact, when it was named in 1977,Caerorhachis was thought to be adendrerpetontid temnospondyl.[2]
The vertebrae ofCaerorhachis are more similar to anthracosaurs, however. As in all early tetrapods, thecentrum, or central part of the vertebra, is composed of two parts: theintercentrum and thepleurocentrum. While temnospondyls have large intercentra and small pleurocentra,Caerorhachis and anthracosaurs have larger pleurocentra than intercentra.[4] A 2003 phylogenetic analysis of early tetrapods placedCaerorhachis outside theclade that included temnospondyls and anthracosaurs in an ancestral position to both groups.[5]
Caerorhachis is thought to have had a primarily terrestrial lifestyle. It lacks thelateral lines across the skull that served as an adaptation for earlier aquatic tetrapods and their ancestors. The large, well developed limbs suggest it was able to move on land better than other early tetrapods likecolosteids andbaphetids. Robert Holmes andRobert L. Carroll, the first to describeCaerorhachis, interpreted it as "[an] animal spending much of its life in the damp mud on the margins of ponds or streams, feeding on stranded fish, or occasionally venturing into the water to catch aquatic larvae of other amphibians."[2]
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