Vertebrate faunas from Triassic fissure deposits of south west Britain
Triassic sediments recovered from fissure and cavity systems in Carboniferous limestone at Cromhall Quarry, Gloucestershire are shown to contain abundant reptilian remains. At least fourteen different genera have been identified from seven different fissure fills, and the different faunal assemblages may represent successional ecosystems. The reptiles are mostly small and the largest, when fully reconstructed, is little more than ore metre long. The fauna includes Clevosaurus, Planocephalosaurus, Diphydontosaurus, Kuehneosaurus and Variodens plus two new sphenodontids, a terrestrial crocodile, two pseudosuchians, a possible aetosaur and at least two other previously undescribed reptiles. The taxonomy of the Sphenodontidae is reviewed, and the taxonomic position of the trilophosaurs examined. Owing to the lack of spores, the precise ages of the fills are difficult to determine, but evidence is presented that suggests they are Upper Triassic but pre-Rhaetic. Palaeoecosystems have been reconstructed for the Cromhall assemblages and these have been compared with modern herpetological communities. It is concluded that the assemblages probably represent semi-arid desert communities and are distinct from the insular habitat normally assumed for Rhaetian palaeoecosystems in the same area. The faunas of some other Mesozoic fissure localities in the Bristol Channel area, including Emborough and Ruthin Quarries, are examined. These deposits are also concluded to be late Norian in age. The primitive mammal Kuehneotherium is recorded from Emborough Quarry. This is the earliest record of a therian mammal and may be the first known "true" mammal.