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We describe and incorporate fragmentary new cranial and postcranial materials of hadrosaurid ornithopods into the non-avian dinosaur assemblage of the Upper Cretaceous (Coniacian–Maastrichtian) Lago Colhué Huapi Formation of central Patagonia, south-central Chubut Province, Argentina. The fossils come from the upper part of the formation, probably from a stratigraphic interval close to the Cretaceous/Paleogene boundary. The materials belong to at least two ontogenetically distinct individuals that are assigned to Hadrosauridae due to their possession of anatomical features that characterize this derived ornithopod group. Sedimentological inferences reveal that the paleoenvironment of these hadrosaurids was characterized by high-sinuosity, meandering-type fluvial channels, whereas palynological data suggest the existence of low-energy freshwater bodies in the floodplains of these rivers and a warm and humid paleoclimate. The deposition of the upper part of the Lago Colhué Huapi Formation was probably influenced by the Patagonian Atlantic marine transgression, which may have played an important role in the distribution of this sedimentary unit. The new Lago Colhué Huapi Formation hadrosaurid specimens constitute the most stratigraphically recent records of this clade from Argentina. The materials contribute to the interpretation of Upper Cretaceous hadrosaurid paleobiogeography in Patagonian basins; moreover, sedimentological and palynological data suggest that paleoenvironmental conditions may have exerted an important influence on South American hadrosaur distribution, supporting hypotheses of ornithopod faunal turnover during the Late Cretaceous of central Patagonia. Finally, the new remains add to the generally depauperate record of Late Cretaceous ornithopods in the Southern Hemisphere. • New remains hadrosaurid ornithopods from the Latest Cretaceous of the Lago Colhué Huapi Formation (Chubut Group, Golfo San Jorge Basin) are reported. • The distribution of Late Cretaceous ornithopods in southern South America was directly related to paleoenvironmental conditions. • The proximity of the paleoshoreline, could have favored hadrosaurids over earlier-diverging ornithopods such as elasmarians. • The Atlantic marine transgression may have played an important role in the distribution of hadrosaurids. [ABSTRACT FROM AUTHOR]

In this paper, we present an updated revision of fossil vertebrates from the Chubut Group, Golfo San Jorge Basin, while also describing some new remains. Extensive exposures of both Lower and Upper Cretaceous sedimentary sequences are present in central Patagonia. These outcrops have, over the past several decades, yielded a varied vertebrate fauna, including fishes, turtles, crocodyliforms, pterosaurs, and dinosaurs, currently herein characterized and described. Although vertebrate diversity in the Chubut Group in central Patagonia is remarkable, the most abundant vertebrates recovered are dinosaurs. The Matasiete Formation (Hauterivian?–Albian) is markedly less prolific in terms of fossils discoveries than either the Bajo Barreal Formation (Cenomanian–early Turonian) or the recently recognized Lago Colhué Huapi Formation (Coniacian–Maastrichtian). The Bajo Barreal fauna is, at a high level, typical of coeval Gondwanan faunas. However, interestingly, several taxa occupy a basal position within their respective groups. The Lago Colhué Huapi Formation has produced a more derived vertebrate fauna, again similar to those from other Gondwanan regions. Finally, in a broad context, the new materials described augment our understanding of Cretaceous terrestrial vertebrate assemblage of central Patagonia and add to the generally meager record of vertebrate in the Cretaceous of the Southern Hemisphere. • South-central Patagonia preserves a rich and important vertebrate fossil record. • New materials described augment our understanding of Cretaceous vertebrate. • The information mentioned constitutes an important source for future comparisons. [ABSTRACT FROM AUTHOR]