The earliest dinosaur-dominated fauna? A reappraisal of the Carnian Lerici tracksite and the first global radiation of Sauropodomorpha

The early evolution and diversification of dinosaurs have been the subject of extensive research, yet the Triassic record of dinosaurs is somewhat fragmentary and ambiguous, especially in units older than the Norian. In addition to skeletons, the tetrapod footprint record can yield a precious source of information, provided that a stable ichnotaxonomy and synapomorphy-based correlations with the potential trackmakers are established. Following these principles, we present a new systematic study on the Carnian tetrapod ichnofauna from Lerici, northwestern Italy. Our results indicate the occurrence of two non-sauropod sauropodomorph ichnospecies (Evazoum sirigui and Eosauropus cimarronensis), one theropod ichnospecies (Grallator isp.), one pseudosuchian ichnospecies (Brachychirotherium parvum), and one ichnotaxon commonly referred to lepidosauromorphs (Rhynchosauroides isp.). In addition, we revise the ichnofamily Otozoidae and the ichnospecies of Evazoum. Based on the First Appearance Datum (FAD) of Evazoum, we introduce the Evazoum tetrapod footprint sub-biochron, which correlates with the Tuvalian–Rhaetian interval. For the first time, we discuss the ankle configuration of the potential producers, identifying clear features for the distinction between pseudosuchian and dinosaur tracks. Since this ichnoassociation is dinosaur-dominated and regarded as early late Carnian in age, it supports the most recent hypotheses on the influence of the Carnian Pluvial Episode (CPE) on the early evolution of dinosaurs. Featuring the earliest co-occurrence of two different sauropodomorph ichnogenera, it provides further evidence for a late Carnian sauropodomorph radiation, which can be recognised over a broad geographic expanse spanning from Argentina to Italy.