Abstract
The most accepted killing model for the Permian-Triassic mass extinction (PTME) postulates that massive volcanic eruption (i.e., the Siberian Traps Large Igneous Province) led to geologically rapid global warming, acid rain and ocean anoxia. On land, habitable zones were drastically reduced, due to the combined effects of heating, drought and acid rains. This hyperthermal had severe effects also on the paleobiogeography of several groups of organisms. Among those, the tetrapods, whose geographical distribution across the end-Permian mass extinction (EPME) was the subject of controversy in a number of recent papers. We here describe and interpret a new Early Triassic (?Olenekian) archosauriform track assemblage from the Gardetta Plateau (Briançonnais, Western Alps, Italy) which, at the Permian-Triassic boundary, was placed at about 11° North. The tracks, both arranged in trackways and documented by single, well-preserved imprints, are assigned to Isochirotherium gardettensis ichnosp. nov., and are here interpreted as produced by a non-archosaurian archosauriform (erytrosuchid?) trackmaker. This new discovery provides further evidence for the presence of archosauriformes at low latitudes during the Early Triassic epoch, supporting a model in which the PTME did not completely vacate low-latitude lands from tetrapods that therefore would have been able to cope with the extreme hot temperatures of Pangaea mainland.
Highlights
The Permian-Triassic mass extinction (PTME) was the most severe biotic crisis of all times (Erwin, 1993), eliminating >90% of marine and terrestrial species
The Gardetta ichnosite is characterized by archosaur-grade footprints assigned to Chirotherium isp. and to the new ichnospecies Isochirotherium gardettensis
They represent the first record of terrestrial tetrapods in the Brianconnais domain of the Western Alps and expand the record of archosaur-grade footprints in the Lower Triassic of Central Europe
Summary
The Permian-Triassic mass extinction (PTME) was the most severe biotic crisis of all times (Erwin, 1993), eliminating >90% of marine and terrestrial species Bernardi et al (2015), Bernardi, Petti & Benton (2018) and Romano et al (2020) reviewed the late Permian-Early Triassic terrestrial tetrapod record integrating skeletal and track data and concluded that tetrapod geographic distribution was much wider than previously suggested. Some of them are badly preserved but distinct trackways, up to 3 m long, can be recognized together with other exceptionally preserved isolated tracks showing clear morphological details of the trackmaker’s autopodium This discovery provides reliable evidence of the presence of archosauriforms in the Brianconnais domain during the Early Triassic, adding further support to the occurrence of terrestrial tetrapods at low latitudes soon after the PTME (Bernardi et al, 2015; Bernardi, Petti & Benton, 2018; Romano et al, 2020) and well-before a full land ecosystem recovery
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