The temnospondyl amphibians from the Viséan of East Kirkton, West Lothian, Scotland

Abstract

ABSTRACTA new temnospondyl amphibian Balanerpeton woodi gen. et sp. nov. is represented by over 30 complete or partial skeletons from the Viséan limestones, shales and tuffs in East Kirkton Quarry, Bathgate, near Edinburgh, Scotland. It is the commonest tetrapod represented in the East Kirkton assemblage and grew to about half a metre in length. Although superficially like the later Dendrerpeton, it is more advanced in possessing small premaxillaries each bearing a pronounced alary process, large external nares, large rounded interpterygoid vacuities, broadly bordered by the vomers anteriorly, a narrow vomer-pterygoid suture and a rod-like stapes. It is characterised by an unusual dental configuration in which each dentary bears a smaller number of larger teeth than the corresponding upper jaw ramus. A second probable temnospondyl is represented by two straight ribs of a much larger form.The relationships of basal temnospondyls and other amphibian groups are discussed and it is proposed that the sister-group of the temnospondyls is the Microsauria and that neither colosteids nor Caerorhachis can be considered to be temnospondyls, as both fall outside the temnospondyl-microsaur clade. A preliminary study of character distribution across a selection of primitive temnospondyls, including Balanerpeton, suggests that it is more advanced than the long-snouted Edopoidea and the Dendrerpetontidae despite its Viséan age. This implies that by the Viséan, significant diversification of temnospondyls had taken place.