Pegadas teromorfóides do Triássico Superior (Formação Santa Maria) do Sul do Brasil

Abstract

Tracks of triassic vertebrates are abundant all over the world, but they were discovered only recently in Santa Maria Formation (Middle-Late Triassic, Southern Brazil), despite the rich osteological record in this unit. The studied material consists of rock samples containing theromorphoid footprints and tracks from Predebon outcrop (upper portion of Alemoa Member, Santa Maria Formation), located in the municipality of São João do Polêsine, Rio Grande do Sul State. Some of the footprints had been attributed to Dicynodontipus isp., while others had been described as Dicynodontipus protherioides isp. nov. Some footprints associated to these could not have been identified, being classified as Incertae sedis. The studied footprints do not correspond to undertracks and were produced in wet and very plastic substrate. After their production, a brief period of subaerial exposure leads to the hardening of the surface before its burial. The trackmaker of Dicynodontipus protherioides isp. nov. was quadrupedal, cursorial, with alternate pace and half-erect gait, but with little lateral movement of the vertebral column; the autopodia were plantigrade to semiplantigrade, without long claws and with falangeal and sole pads. The tracks were produced in walking gait with the tail touching the ground. The gleno-acetabular distance of the trackmaker was calculated as 2.68 cm. The studied footprints, including Dicynodontipus protherioides isp. nov. and Dicynodontipus isp., can be attributed to small-sized cynodonts, whose skeletons are found in the Santa Maria and Caturrita formations.