The first tetrapod track recorded from the Rhaetian in the British Isles

Abstract

Terrestrial vertebrate trace fossils are relatively abundant in mid-to-late Triassic and early Jurassic deposits in the British Isles but to date none at all have been recorded from the Rhaetian, the final stage of the Triassic. This represents a persistent gap in the terrestrial ichnological record. We present the first Rhaetian track to be recognised in the British Isles, found at Aust Cliff on the south bank of the Severn Estuary near Bristol in SW England. This locality is well known for disarticulated remains of Rhaetian fossil reptiles including some terrestrial species but in 2006 a track (TECMAG0161) was found for the fist time. Although the specimen was found ex-situ the palynological data from the surrounding matrix confirms a Rhaetian age. The track was examined with CT scanning and photogrammetry. We tentatively assign the track to the ichnogenus Procolophonichnium based on size and digit proportions. The isolated nature of the specimen offers little concrete information about the track maker but such tracks have previously been attributed to parareptiles or therapsid trackmakers. The specimen adds a datapoint to an otherwise ichnologically empty period of time in the British Isles. The track also provides solid evidence for a [locally] terrestrial environment in a sequence that is otherwise considered predominantly marine or estuarine. This discovery suggests that there may be more such tetrapod tracks of Rhaetian age preserved, at least at Aust, and further searching will hopefully lead to the current minimal dataset being expanded.