Time for Giants: Titanosaurs from the Berriasian–Santonian Age

Abstract

Titanosaurian sauropods were the most diverse and successful group of large-bodied terrestrial herbivores. Two aspects regarding their evolutionary history stand out, namely their great morphological diversity and their extensive record from various continental masses. In South America, and particularly in Argentina, the group has the richest record worldwide. This is mainly due to the conjunction of two factors: the extensive paleontological investigation carried out by South American researchers since the beginning of the twentieth century and the well-exposed outcrops of Cretaceous continental strata. With the exception of Tapuiasaurus from Brazil, the entire record of South American named titanosaurs discovered in the Berriasian–Santonian interval comes from Argentina, specifically from Patagonia, including the south of Mendoza, Neuquén, Río Negro, and Chubut Provinces. With a number of 22 valid taxa, the Early and ‘Mid’-Cretaceous titanosaur record of South America includes basally branching (‘basal’) forms (e.g., Andesaurus, Ninjatitan), basal and derived lithostrotians (e.g., Sarmientosaurus, Tapuiasaurus, and Epachthosaurus), and most of the colossosaurs (mainly the giant lognkosaurs Mendozasaurus, Futalognkosaurus, Patagotitan, and Notocolossus). After their origin in the Early Cretaceous, titanosaurians experienced a rapid increase in taxonomic diversity, which is maintained toward the Late Cretaceous. However, during the Berriasian–Santonian interval, the size of titanosaurs reached its climax, representing the largest vertebrate animals ever to inhabit the earth. Some South American titanosaurs from this time have been widely used to define new clades (e.g., Colossosauria, Lognkosauria, Rinconsauria) that clarified the main phylogenetic relationships at lower level. Moreover, studies in some key paleobiological aspects related with the estimation of size contributed to better understanding the biology of some species in the context of the process of gigantism.