This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A research team led by Dr. Lorenzo Marchetti of the Museum für Naturkunde Berlin described the earliest archosauriform footprints (Pachychirotherium gardenaensis) from the GEOPARC Bletterbach—UNESCO World Heritage Dolomites, Italy.
The study found that the transition from sprawling to erect locomotion was a stepwise process that started in the late Permian and was completed only by the Middle Triassic, leading shortly afterward to the acquisition of bipedality among the first dinosaurs and dinosaur relatives. The study was published in the journal Palaeontology. Archosaurs are iconic animals that ruled the Mesozoic, with dinosaurs being their most derived group.
Their direct ancestors, the archosauriforms, appeared during the late Permian, shortly before the catastrophic end-Permian extinction. However, their fossil record in the Permian is scattered. Additional information comes from their footprints, which were first found in the GEOPARC Bletterbach—UNESCO World Heritage Dolomites, Italy.
Until now, this material has been considered similar to Early Triassic archosauriform footprints such as Protochirotherium, known from Germany, Poland and Morocco. It has also been assumed that these footprints indicated an erect stance while the animals walked. As part of a research project on archosauriform footprints carried out at the Museum für Naturkunde Berlin, Marchetti, in collaboration with Hendrik Klein of Saurierwelt, reanalyzed the material along with some newly described specimens.
These footprints are now stored at the University "La Sapienza" of Rome and the Naturmuseum Südtirol in Bozen (Italy). The scientists concluded that these specimens belong to the ichnofamily Chirotheriidae and are taxonomically different from all other footprints belonging to this group. They named these footprints Pachychirotherium gardenaensis, meaning "thick chirotheriid from Gardena." A comparative study of Pachychirotherium and the feet and hands of archosauriforms, based on morphology and measurements, allowed the scientists to attribute these footprints to archosauriforms and, more specifically, to Erythrosuchidae or animals with very similar limb morphology.
An additional analysis of archosauriform trackways from the Permian and Triassic revealed a stepwise transition in these animals' walking posture from sprawling (in the late Permian) to erect (by the Middle Triassic). This occurred alongside an increase in cursoriality (longer middle digits of the foot) and digitigrady (only the digits touched the ground), as well as a reduction in the size of the hands. All of these features were essential for the later evolution of bipedality in dinosaurs and their close relatives.
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