Pterosaur tracks from the Purbeck Limestone Formation of Dorset, England

Abstract

Purbeckopus pentadactylus , an unusual vertebrate track, is found in the Intermarine Member of the Purbeck Limestone Formation (Lower Cretaceous) of southern England. Only three slabs of biosparrudite containing the trace fossil have been found. These rocks were deposited on intertidal to supratidal flats. Purbeckopus is a quadrupedal vertebrate trace comprising a tetradactyl elongate subtriangular plantigrade pes and an elongate tridactyl manus. It is very similar to the ichnogenus Pteraichnus (Stokes) and it seems likely that both tracks were made by the same type of animal. Re-examination of Purbeckopus led us to the conclusion that it is probably pterosaurian in origin. This conclusion is based on two main features of the tracks. Firstly, the pes tracks show indications of elongate penultimate phalanges, a pterosaur characteristic. Secondly, the trackway has an unusual configuration wherein the impression of the manus lies well outside that of the pes. Only an animal with forelimbs longer than hind limbs would be likely to make such a track. The pterosaur that produced Purbeckopus is calculated to have had a wingspan of approximately 6 m. The identification of Purbeckopus as a pterosaur track indicates that large pterosaurs must have existed somewhat earlier than previously thought.