Bipedal leaping Jurassic vertebrates in Southern Africa: proposed new ichnotaxon and inferred palaeoenvironment

Abstract

The Lower Jurassic Clarens Formation (Stormberg Group, Karoo Supergroup, Main Karoo basin) contains relatively common vertebrate trackways impressed into apparently soft to firm, fine sediment beds preserved within the succession. At least three known ichnotaxa are interpreted as leaping bipedal vertebrates. Here we provide a generic description of a proposed new ichnotaxon to add to this small group of the oldest known bipedal hopping vertebrates in Africa and globally. Saltirecarpipes Genus Nova (Type Species tinleyi) (saltus – leap; carpe – seize; pes – foot) has been identified from tracks at Giants Castle in the KwaZulu-Natal Drakensberg. The type specimen in the National Museum Bloemfontein exhibits two adjacent tetradactyl impressions with four digits extended from metatarsal pads, comprising three inner digits grouped closer together and facing forwards, the fourth digit being much longer and curved outwards and slightly backwards. The digits are all strongly curved with claw impressions being preserved in several cases. These were small vertebrates, a leap length of ca. 180 mm being inferred. Being found in association with trace fossils of Equisitales (horse tails) a wet palaeoenvironment of small ponds is postulated. These appear to have been associated with distal fan sheetflood deposits of fine sediment at Giants Castle, which pass laterally into more central-basinal palaeodune deposits which characterise the Clarens Formation across the Main Karoo depository. The new ichnotaxon appears to have been restricted to wet desert marginal settings, feeding immature sediment to the desert basin, and which retreated proximally as aridification of the Clarens palaeoenvironment progressed.