Late Triassic terrestrial microvertebrates from Charles Moore's 'Microlestes' quarry, Holwell, Somerset, UK

Abstract

The fissure localities of the Bristol region and South Wales have yielded some of the most important Late Triassic and Early Jurassic small tetrapods. The 'Microlestes' quarry fissure at Holwell, which has produced the most diverse overall fauna, was originally investigated in the 1850s by the renowned amateur geologist, Charles Moore. The mammaliamorphs and marine fish have been well documented, but there are few reports and barely any descriptions of the terrestrial small reptile fossils. We address that deficiency with a description of the bones and teeth that can be assigned to the Reptilia, confirming the presence of Diphydontosaurus and describing two new rhynchocephalians. We recognise the presence of Variodens inopinatus Robinson, 1957 and Gephyrosaurus Evans, 1980: the first time that they have been recorded outside their original sites. Additionally, we record a procolophonid, elements of the actinopterygian Pholidophorus, and a number of unnamed lepidosaur specimens that show varying degrees of pleurodont-acrodont implantation, providing an insight into the evolution of rhynchocephalians. Our findings demonstrate that Holwell is a key link between the sauropsid and mammaliamorph fissure faunas of the Late Triassic and Early Jurassic of the south-west UK.