During the Late Triassic epoch (237–201 million years ago), the terrestrial ecosystems of Pangaea underwent drastic changes1,2 that led to the rise and diversification of mammaliaforms3, crocodylomorphs4 and dinosaurs5. Although the Carnian sedimentary rocks of South America provided much of the available evidence for understanding the early evolution of these clades, key discoveries have remained restricted to the Ischigualasto-Villa Unión6,7 and Paraná basins8 in Argentina and Brazil, respectively. Here we report a Carnian tetrapod assemblage from the previously unrecognized Northern Precordillera Basin in northwestern Argentina. Discoveries at this basin, in the Quebrada Santo Domingo site, include a nearly complete skeleton of the early sauropodomorph Huayracursor jaguensis gen. et sp. nov., and typical components of Late Carnian faunas, such as hyperodapedontine rhynchosaurs, gomphodontosuchine traversodontid cynodonts, and aetosaurs. Compared to its generally small and short-necked Carnian counterparts9,10, Huayracursor is larger and exhibits an incipient elongation of its cervical vertebrae, representing an intermediate condition for size and cervical elongation between known Carnian and Norian sauropodomorphs11. This discovery provides one of the oldest pieces of evidence of increased body mass and neck elongation in early Sauropodomorpha.
