PTEROSAUR TRACKS FROM THE PURBECK LIMESTONE FORMATION OF DORSET, ENGLAND

Purbeckopus pentadactylus, an unusual vertebrate track, is found in th e Intermarine Member of the Purbeck Limestone Formation (Lower Cretace ous) of southern England. Only three slabs of biosparrudite containing the trace fossil have been found. These rocks were deposited on inter tidal to supratidal flats. Purbeckopus is a quadrupedal vertebrate tra ce comprising a tetradactyl elongate subtriangular plantigrade pes and an elongate tridactyl manus. It is very similar td the ichnogenus Pte raichnus (Stokes) and it seems likely that both tracks were made by th e same type of animal. Re-examination of Purbeckopus led us to the con clusion that it is probably pterosaurian in origin. This conclusion is based on two main features of the tracks. Firstly, the pes tracks sho w indications of elongate penultimate phalanges, a pterosaur character istic. Secondly, the trackway has an unusual configuration wherein the impression of the manus lies well outside that of the pes. Only an an imal with forelimbs longer than hind limbs would be likely to make suc h a track. The pterosaur that produced Purbeckopus is calculated to ha ve had a wingspan of approximately 6 m. The identification of Purbecko pus as a pterosaur track indicates that large pterosaurs must have exi sted somewhat earlier than previously thought.