No abstract

In the dusk of the dinosaur era, the advanced duck-billed dinosaurs (Family Hadrosauridae) are thought to have outcompeted other herbivores, making ecosystems less diverse and more vulnerable to the Cretaceous-Paleogene asteroid impact. They were also among the first terrestrial organisms to disperse from North America into South America. Here, we present the first new species of subantarctic duck-billed dinosaur, CPAP 3054, of early Maastrichtian age in Magallanes, Chile. Surprisingly, unlike duckbills further north in Patagonia, CPAP 3054 is not an advanced duckbill, but descends from North American forms that were transitional to Hadrosauridae, diverging shortly before the origin of this family. In North America, these forms were replaced by hadrosaurids in the late Campanian. The survival into the Maastrichtian of a pre-hadrosaurid lineage suggests the ancestors of CPAP 3054 arrived earlier in South America than the hadrosaurids, reaching further south before the Cretaceous-Paleogene mass extinction, where they avoided competition from hadrosaurids.Additional noteThis work contains a new biological name. New names in preprints are not considered available by the ICZN. To avoid ambiguity, the new biological name is not included in this preprint, and the holotype specimen number CPAP 3054 is used as a placeholder. Paratypes described in this preprint are also used in the diagnosis.

In this study, new isolated fragmentary pterosaur bones are described from Lower Cretaceous outcrops exposed at Cerro La Isla, a site located approximately 95 km east of Copiapó city, Atacama region, northern Chile. The material consists of a jaw fragment with broken teeth, the caudal portion of a mid-cervical vertebra and the distal portion of a femur. Based on their morphology, the jaw and cervical fragments are assigned to Ctenochasmatidae, a group of pterodactyloid pterosaurs that has been previously reported from this locality, while the femur lacks diagnostic characters that would allow its referral to a more exclusive taxon than Pterodactyloidea indet. This new material confirms the previously proposed presence of ctenochasmatid pterosaurs in the Cretaceous outcrops of Cerro La Isla, and increases the diversity of their skeletal elements discovered at the site.

In the dusk of the Mesozoic, advanced duck-billed dinosaurs (Hadrosauridae) were so successful that they likely outcompeted other herbivores, contributing to declines in dinosaur diversity. From Laurasia, hadrosaurids dispersed widely, colonizing Africa, South America, and, allegedly, Antarctica. Here, we present the first species of a duck-billed dinosaur from a subantarctic region, Gonkoken nanoi , of early Maastrichtian age in Magallanes, Chile. Unlike duckbills further north in Patagonia, Gonkoken descends from North American forms diverging shortly before the origin of Hadrosauridae. However, at the time, non-hadrosaurids in North America had become replaced by hadrosaurids. We propose that the ancestors of Gonkoken arrived earlier in South America and reached further south, into regions where hadrosaurids never arrived: All alleged subantarctic and Antarctic remains of hadrosaurids could belong to non-hadrosaurid duckbills like Gonkoken . Dinosaur faunas of the world underwent qualitatively different changes before the Cretaceous-Paleogene asteroid impact, which should be considered when discussing their possible vulnerability.