Fig 1.
Pes and manus imprints of cf. Protochirotherium.
A, left pes imprint PZO 1111 from the Arenaria di Val Gardena (Upper Permian) of the Deutschnofen/Nova Levante locality in northern Italy preserved as a natural cast. B, interpretative drawing. C, Protochirotherium wolfhagense pes-manus set (Holotype) from the Detfurth Formation (Lower Triassic, Olenekian) of Germany. D, interpretative drawing.
Fig 2.
Chirotheriid and possible chirotheriid pes and manus imprints from the Arenaria di Val Gardena (Upper Permian) of northern Italy.
A, possible manus imprint MGR 0032. B, pes or manus imprint N.S. 34/82. C, pes or manus imprint NMS 1235 (Inv. No. 2498). D, pes or manus imprint R6. E, deeply impressed pes imprint MUSE 7446. F, tetradactyl pes or manus imprint NMS 1.
Fig 3.
Time-calibrated cladogram of archosauromorhs discussed in the text based on skeletal remains only.
Highly debated relatioships have been collapsed into polytomies. We here depict their position after [1,9,118–123]. Geological timescale after [193].
Fig 4.
A, right pes skeleton of Protorosaurus speneri NHMW 1943I4, Naturhistorisches Museum Wien, Vienna, Austria. B, interpretative drawing. C, right pes skeleton of Euparkeria capensis SAM PK K8309. D, Intepretative drawing. Note that Protorosaurus has an ectaxonic pes, with digit IV>III>II>I while Euparkeria shows a mesaxonic foot with III being the longest.
Fig 5.
Evolution of the mesaxonic pes in archosauromorphs.
Grey and black boxes indicate evolution of apomorphic characters: grey = ectaxony, black = mesaxony. Late Permian Protochirotherium pulls the evolution of mesaxony down the archosauriform tree and anticipates the oldest skeletal remain (Euparkeria capensis) by 10 Ma.
Fig 6.
Paleogeographic distribution of Late Permian archosauriform footprints (yellow stars) and body fossil (black shapes) localities across Pangea.
Squares = indeterminate archosauromorphs, circles = non-archosauriform archosauromorphs, stars = archosauriforms. Chirotheriid footprints from the southern Alps (NE Italy) document the lowest palaeolatitudinal record of archosauriforms and bridge the tropical gap in the disjunct distribution of the skeletal record. Paleomap for 260 Ma downloaded from Fossilworks using data from the Paleobiology Database [194].
Fig 7.
Paleogeographic distribution of Early Triassic archosauriform footprints (yellow stars) and body fossil (black shapes) localities across Pangea.
Squares = indeterminate archosauromorphs, circles = non-archosauriform archosauromorphs, stars = archosauriforms. Footprints indicate that archosauriforms, soon after their origin, were distributed also at low latitudes. Paleomap for 250 Ma downloaded from Fossilworks using data from the Paleobiology Database [194].
Fig 8.
Archosauriform body size through time as derived from track length.
Average track size indicates that archosauriform body size did not change significantly from the Late Permian to Early Triassic, although maximum values show a significant increase. The Permo-Triassic mass exctintion might not have affected archosauriform body size. Based on data of S1 Table.
Fig 9.
Depositional environment of late Permian and Early Triassic archosauromorph-bearing formations.
The common pattern exhibited by the body fossil and the track fossil record suggest a real environmental/ecological preference for inland-fluvial (lacustrine) environments for early archosauromorphs.