EARLY TRIASSIC THERAPSID FOOTPRINTS FROM THE SYDNEY BASIN, AUSTRALIA

A large rock slab collected in 1913 from the roof of the Bellambi Coll iery in the southern Sydney Basin bears fossil tracks that are now kno wn from recent radiometric and chemostratigraphic dating to be earlies t Triassic, rather than latest Permian, in age. The tracks show two di stinctive features of reptiles: scale impressions and claw marks. Both manus and pes are pentadactyl, ectaxonic, semidigitigrade and have an outer interdigital angle (digits IV-V) greater than inner interdigita l angles. Digit proportions are consistent with a phalangeal formula o f 23333. The fossil tracks are referred to the ichnospecies Dicynodont ipus bellambiensis sp. nov. They are similar to the kinds of tracks th ought to be produced by Lystrosaurus species. Given the abundance of t hese species in Early Triassic faunas of low diversity and the occurre nce of members of the Lystrosaurus fauna in Queensland and Antarctica, chances are good that this is indeed a trackway of Lystrosaurus. If c onsidered to be made by an animal of that type, the trackway was produ ced using the primitive alternate gait, rather than the mammalian ambl e, by an animal about 84 cm long and some 22 cm high. Preservation of bones of these creatures would not be expected given the non-calcareou s nature of associated fossil soils in the Sydney Basin Triassic. Herb aceous lycopods, locally common in these and other Early Triassic stra ta worldwide, are among the most likely foods of these tusked, low-bro wsing herbivores.