Ichnotaxonomy, biostratigraphy and palaeoecology of the Monti Pisani tetrapod ichnoassociation (Tuscany, Italy) and new insights on Middle Triassic Dinosauromorpha

The Middle Triassic is a key time span for understanding the evolution of archosaurs and the rise of Dinosauromorpha. A further source of information on this issue may be provided by the study of tetrapod footprints. We revise the tetrapod ichnoassociation of the Quarziti del Monte Serra Formation (Verrucano Group, Monti Pisani, Italy) and identify the following ichnotaxa: cf. Atreipus isp. (dinosauromorph), Chirotherium barthii, C. gallicum (archosauriforms), Rotodactylus isp. and Synaptichnium pseudosuchoides (archosauromorphs), Rhynchosauroides cf. palmatus (neodiapsid), cf. Circapalmichnus isp. and Procolophonichnium haarmuehlensis (therapsids). The ichnoassemblage is diverse and dominated by Rhynchosauroides tracks in the coastal pond deposits and non-diverse and dominated by archosaur tracks in the coastal sandflat deposits. Bivalve biostratigraphy supports the Ladinian age of the Quarziti del Monte Serra Formation inferred by the tetrapod ichnoassociation. The stratigraphically oldest occurrences of Atreipus from Italy, France, Morocco and Germany are likely Ladinian, which highlights a wide dispersal of dinosauromorphs as early as the Middle Triassic.