Two Late Cretaceous sauropods reveal titanosaurian dispersal across South America

Abstract

South American titanosaurians have been central to the study of the evolution of Cretaceous sauropod dinosaurs. Despite their remarkable diversity, the fragmentary condition of several taxa and the scarcity of records outside Patagonia and southwestern Brazil have hindered the study of continental-scale paleobiogeographic relationships. We describe two new Late Cretaceous titanosaurians from Quebrada de Santo Domingo (La Rioja, Argentina), which help to fill a gap between these main areas of the continent. Our phylogenetic analysis recovers both new species, and several Brazilian taxa, within Rinconsauria. The data suggest that, towards the end of the Cretaceous, this clade spread throughout southern South America. At the same locality, we discovered numerous accumulations of titanosaurian eggs, likely related to the new taxa. With eggs distributed in three levels along three kilometres, the new site is one of the largest ever found and provides further evidence of nesting site philopatry among Titanosauria.

A new giant sauropod,Australotitan cooperensisgen. et sp. nov., from the mid-Cretaceous of Australia

“…In the absence of such a resolved phylogeny, we can consider the phylogenetic position of A. cooperensis using a comparative approach, using published phylogenies and the spread of characteristics hypothesized to define particular clades. The phylogenetics of titanosaurians remains in a state of flux with multiple assessments appearing in recent years investigating the relative position of taxa in a global context, covering Late Jurassic to Late Cretaceous (Carballido et al, 2017;D'Emic, 2012;González Riga et al, 2019;Gonzàlez Riga et al, 2018;Hechenleitner et al, 2020;Mannion, Allain & Moine, 2017;Mannion et al, 2013;Mannion et al, 2019a;Mannion et al, 2019b).…”

“…The relative phylogenetic position of W. wattsi as basal to D. matildae has changed since the first phylogenetic assessment was undertaken (Hocknull et al, 2009) and further since the addition of S. elliottorum (Poropat et al, 2016). W. wattsi has been resolved as a non-titanosaurian somphospondylan (Hocknull et al, 2009;Poropat et al, 2015a), but has also been recovered outside of titanosauriformes (Carballido et al, 2011b;Hechenleitner et al, 2020); more derived than D. matildae (Mannion et al, 2013); within the titanosaurian 'Andesauroidea'; or sister taxon to the Titanosauria (Mannion et al, 2019a).…”

First titanosaur dinosaur nesting site from the Late Cretaceous of Brazil

“…Titanosaurs were a group of successful quadrupedal herbivorous sauropod dinosaurs distributed worldwide during the Cretaceous 1 , 2 that achieved the largest sizes for animal on terrestrial environments 3 , 4 . They have a mainly Gondwanan distribution 1 , 5 , 6 , with a peak of abundance and diversity during the Late Cretaceous in South America 2 , 7 , 8 .…”

The Axial Skeleton of Rinconsaurus caudamirus (Sauropoda: Titanosauria) from the Late Cretaceous of Patagonia, Argentina

“…Despite being one of the most successful and diverse lineages of sauropods, the evolution of Titanosauria is far from being well known, possibly due to the fragmentary nature of many of their taxa and the lack of in-depth anatomical studies of taxa that have been disclosed only preliminary. This is reflected in the poor resolution of phylogenetic analyzes, which has generated a strong debate about the interrelationships of Titanosauria and the main aspects linked to its evolution (eg, Salgado et al, 1997;Wilson and Sereno, 1998;Upchurch, 1998;González Riga et al, 2013;Coria et al, 2013;Gallina and Otero, 2015;Salgado et al, 2015, Carballido et al, 2017González Riga et al, 2018;Gorscak and O'Connor, 2019;Mannion et al, 2019;Hechenleitner et al, 2020;Gallina et al, 2021). In this sense, to understand the evolution of this group of derived sauropods in a more complete way, detailed anatomical studies of those taxa briefly described are necessary.…”

“…Rinconsauria and Aeolosaurini are usually hypothesized as being closely related (Calvo and González Riga, 2003;Calvo et al, 2007b;Gallina and Apesteguía, 2011;González Riga et al, 2013;Coria et al, 2013;Gallina and Otero, 2015;Salgado et al, 2015, Carballido et al, 2017González Riga et al, 2018;Gorscak and O'Connor, 2019;Mannion et al, 2019), but analyses vary greatly in resolving their members' precise interrelationships. Recently, some phylogenetic analyses have recovered Rinconsauria as sister group to Lognkosauria, forming part of the recently defined clade Colossosauria, with members of Aeolosaurini resolved in various phylogenetic positions outside Colossosauria (e.g., González Riga et al, 2019;Mannion et al, 2019;Hechenleitner et al, 2020;Gallina et al, 2021). Rinconsaurus and Muyelensaurus were both only briefly described and figured, despite being the specifiers of Rinconsauria.…”