First record of Macrocollum itaquii (Dinosauria: Sauropodomorpha) outside the type locality and its biostratigraphic significance

Abstract

ABSTRACT The early radiation of dinosaurs was an evolutionary event characterized by distinct episodes. While the earliest unequivocal records are from Carnian strata and relatively well-documented, the subsequent moment of dinosaur radiation is poorly studied. The fossil record of early Norian dinosaurs from Brazil provides one of the best samples regarding the dawn of the “Prosauropod Empire”. In the present study, we describe the first occurrence of Macrocollum itaquii outside its type locality and discuss its biostratigraphic implications. This dinosaur is of particular interest due to its significance as the oldest sauropodomorph with an elongated neck, expressing the typical body plan seen in post-Carnian sauropodomorphs. The new specimen consists of a partial posterior autopodium, sharing anatomical features exclusively with M. itaquii among sauropodomorphs. The presence of this unaysaurid at the “Boi da Guampa Torta” site allows the biostratigraphic correlation with the “Wachholz” site. According to the phylogenetic affinities of M. itaquii (which is more derived than Pampadromaeus barberenai and Bagualosaurus agudoensis), both fossiliferous sites are younger than the “Várzea do Agudo” site. Nevertheless, further specimens are necessary in order to determine the position of the sites with M. itaquii in relation to the other surrounding outcrops (i.e., Siriusgnathus-bearing outcrops).