Lacertoid footprints from the Upper Triassic (Santa Maria Formation) of Southern Brazil

Abstract

The Triassic of Southern Brazil is well-known for its rich tetrapod body fossils. However, trace fossils such as tetrapod trackways and trails were discovered only recently from the Predebon outcrop (upper part of the Alemoa Member, Santa Maria Formation), providing new information on small-sized animals. The trackways can be identified as Rhynchosauroides retroversipes isp. nov., Rhynchosauroides isp., Rhynchosauroides? isp. and drag marks produced by swimming animals of lacertoid affinity. The preservation of the tracks and trackways was influenced by the water level whilst they were being made and subsequent subaerial exposure. The trackmaker of R. retroversipes isp. nov. corresponds to a lacertoid quadruped tetrapod with primitive autopodia, a sprawling gait and possibly a long tail, whilst the pes was directed postero-laterally. The trackmaker may have been a climbing animal, with adaptations that include curved claws and reversion of the pes. On the ground this animal would have had a slow, lumbering locomotion, although it could attain higher speeds over short distances using a bipedal gait. These trackways can be attributed to lacertoid reptiles, possibly sphenodontids, whose skeletons are encountered in the Caturrita Formation, which overlies the Santa Maria Formation.