Paleontological discoveries in the Chorrillo Formation (upper Campanian-lower Maastrichtian, Upper Cretaceous), Santa Cruz Province, Patagonia, Argentina

Fernando E Novas ,Sebastián Rozadilla,Leonardo Salgado,Gastón Lo Coco,Sergio Bogan,Federico Brissón-Eli,Mariela Soledad Fernández ,Federico Agnolín ,Agustín G Martinelli ,Alexis Mauro Aranciaga-Rolando ,Nicolás Roberto Chimento ,Julia D ́Angelo ,Fátima Brito ,Mauricio A Cerroni ,Matías J Motta ,Jordi A Garcia-Marsà ,Ezequiel Ignacio Vera ,Adriel Roberto Gentil ,Gerardo P Álvarez-Herrera ,Valeria Susana Pérez Loinaze ,Sergio Eduardo Miquel ,Martín D Ezcurra

doi:10.22179/revmacn.21.655

Fernando E Novas , Sebastián Rozadilla + Show 20 more

Open Access

https://doi.org/10.22179/revmacn.21.655

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Abstract

The first fossil remains of vertebrates, invertebrates, plants and palynomorphs of the Chorrillo Formation (Austral Basin), about 30km to the SW of the town of El Calafate (Province of Santa Cruz), are described. Fossils include the elasmarian (basal Iguanodontia) Isasicursor santacrucensis gen. et sp. nov., the large titanosaur Nullotitan glaciaris gen. et sp. nov., both large and small Megaraptoridae indet., and fragments of sauropod and theropod eggshells. The list of vertebrates is also composed by the Neognathae Kookne yeutensis gen. et sp. nov., two isolated caudal vertebrae of Mammalia indet., and isolated teeth of a large mosasaur. Remains of fishes, anurans, turtles, and snakes are represented by fragmentary material of low taxonomical value, with the exception of remains belonging to Calyptocephalellidae. On the other hand, a remarkable diversity of terrestrial and freshwater gastropods has been documented, as well as fossil woods and palinological assemblages. The Chorrillo Formation continues south, in the Las Chinas River valley, southern Chile, where it is called Dorotea Formation. Both units share in their lower two thirds abundant materials of titanosaurs, whose remains cease to appear in the upper third, registering only elasmarians (Chorrillo Formation) and hadrosaurs (Dorotea Formation). Above both units there are levels with remains of invertebrates and marine reptiles. It is striking that the dinosaurs of the lower two thirds of the Chorrillo and Dorotea formations are represented by large basal titanosaurs and Megaraptoridae coelurosaurs, being the Saltasaurinae and Aeolosaurinae sauropods and Abelisauridae theropods totally absent. In contrast, these taxa are dominant components in sedimentary units of central and northern Patagonia (e.g., Allen, Los Alamitos, La Colonia formations). Such differences could reflect, in part, a greater antiquity (i.e., late Campanian-early Maastrichtian) for the Chorrillo fossils, or, more probably, different environmental conditions. Thus, knowledge of the biota of the southern tip of Patagonia is expanded, particularly those temporarily close to the K-Pg boundary.

Highlights

The Chorrillo Formation (Upper Cretaceous, Campanian-Maastrichtian; Arbe, 2002; Nullo et al, 2006) extensively crops out to the south of Centinela River, Santa Cruz Province, southern Patagonia, Argentina (Figure 1)
It is striking that the dinosaurs of the lower two thirds of the Chorrillo and Dorotea formations are represented by large basal titanosaurs and Megaraptoridae coelurosaurs, being the Saltasaurinae and Aeolosaurinae sauropods and Abelisauridae theropods totally absent
We identify a succession of at least four different dinosaur assemblages from beds exposed in the SW corner of Santa Cruz: the oldest ones corresponding to the Cenomanian Mata Amarilla Formation, the Campanian Cerro Fortaleza Formation, the upper Campanian – lower Maastrichtian Chorrillo Formation, and the upper Maastrichtian hadrosaurid-bearing levels of the Dorotea Formation

Summary

Introduction

The Chorrillo Formation (Upper Cretaceous, Campanian-Maastrichtian; Arbe, 2002; Nullo et al, 2006) extensively crops out to the south of Centinela River, Santa Cruz Province, southern Patagonia, Argentina (Figure 1). Feruglio (in Fossa Mancini et al, 1938) was the first to call “Estratos de Chorrillo” (i.e., “Chorrillo Beds”) to these rocks cropping out to the south of the Argentino Lake, indicating the presence of fossil logs and dinosaur bones (Feruglio, 1944-45). Aside from these citations concerning the presence of unspecified dinosaur remains, the first to discover a partial sauropod skeleton was Francisco Nullo in 1980, geologist of Argentine Geological Survey, while exploring the top of the hills of the Alta Vista farm (“estancia”). Bonaparte collected (but did not describe) some isolated theropod remains, including a partial ulna and a shed tooth, forming part of the Paleontological Collection of the Museo Argentino de Ciencias Naturales, in Buenos Aires

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