An overview of the appendicular skeletal anatomy of South American titanosaurian sauropods, with definition of a newly recognized clade.

Bernardo J González Riga,Lucio M Ibiricu,Matthew C Lamanna,Alejandro Otero,Leonardo D Ortiz David,Alexander W.A Kellner

doi:10.1590/0001-3765201920180374

Abstract

In the last two decades, the number of phylogenetically informative anatomical characters recognized in the appendicular skeleton of titanosaurian sauropod dinosaurs has increased dramatically with the discovery of new and comparatively complete specimens. Here we provide an overview of the appendicular skeletal morphology of South American titanosaurs and discuss its significance for phylogenetic reconstruction. The appendicular skeletal diversity of South American titanosaurs is substantially greater than was initially appreciated. Moreover, some regions of the appendicular skeleton, such as the pes, exhibit remarkable variability in form. Multiple synapomorphies of Titanosauria and the less inclusive clades Lithostrotia and Saltasauridae consist of characters of the girdles and limbs. Although the phylogenetic definitions of titanosaurian clades such as Saltasaurinae and Lognkosauria are stable, the taxonomic content of these clades has varied in recent analyses depending on the phylogenetic topology recovered. Within Titanosauria, the results of four recent, largely independent analyses support the existence of a derived titanosaurian lineage distinct from the 'Saltasaurinae line,' which is herein termed Colossosauria. At present, this clade is mainly comprised by taxa within Lognkosauria and Rinconsauria, and is useful in discussions of titanosaurian lower-level relationships.

Highlights

Anatomical and phylogenetic analyses of titanosaurs are crucial for deciphering the evolutionary history and paleobiology of these singular animals, but such studies have been hampered by missing data, as the osteology of many titanosaurian species is not well understood
The morphology of the appendicular skeleton has been extensively documented in only a few taxa, such as Bonitasaura (Apesteguía 2004, Gallina and Apesteguía 2015), Diamantinasaurus (Hocknull et al 2009, Poropat et al 2015), Dreadnoughtus (Lacovara et al 2014, Ullmann and Lacovara 2016), Epachthosaurus (Martínez et al 2004), Neuquensaurus (Otero 2010), Opisthocoelicaudia (Borsuk-Bialynicka 1977), Rapetosaurus (Curry Rogers 2009), and Saltasaurus (Powell 1992, 2003)
We provide an overview of titanosaurian appendicular skeletal anatomy, focusing on the many representatives of this clade that have been recovered from the Cretaceous of South America

Summary

Introduction

Titanosaurian sauropods were the most diverse and abundant large-bodied terrestrial herbivores in the Southern Hemisphere landmasses during the Late Cretaceous (Bonaparte and Powell 1980, Calvo and Bonaparte 1991, Bonaparte and Coria 1993, Bonaparte 1996, Jain and Bandyopadhyay 1997, Salgado et al 1997, Curry Rogers and Forster 2001, Smith et al 2001, Powell 2003, Wilson and Upchurch 2003, Upchurch et al 2004, Curry Rogers 2005, Wilson 2006, Hocknull et al 2009, González Riga 2011, Wilson et al 2011, Curry Rogers and Wilson 2014, Gorscak et al 2014, 2017, Lacovara et al 2014, Otero and Salgado 2015, Poropat et al 2015, 2016, González Riga et al 2016, 2018, Gorscak and O’Connor 2016, Carballido et al 2017, Sallam et al 2018). Anatomical and phylogenetic analyses of titanosaurs are crucial for deciphering the evolutionary history and paleobiology of these singular animals, but such studies have been hampered by missing data, as the osteology of many titanosaurian species is not well understood This situation is beginning to change with recent discoveries and descriptions of wellpreserved, comparatively complete specimens of taxa such as Tapuiasaurus from the Early Cretaceous of Brazil (Zaher et al 2011, Wilson et al 2016), Bonitasaura (Apesteguía 2004, Gallina 2011, Gallina and Apesteguía 2011, 2015), Dreadnoughtus (Lacovara et al 2014, Ullmann and Lacovara 2016, Voegele et al 2017), Epachthosaurus (Martínez et al 2004), Futalognkosaurus (Calvo et al 2007a, b), Mendozasaurus (González Riga 2003, 2005, González Riga et al 2018), Overosaurus (Coria et al 2013), and Patagotitan (Carballido et al 2017) from the mid- and Late Cretaceous of Argentina; Rapetosaurus (Curry Rogers and Forster 2001, 2004, Curry Rogers 2009) from the latest Cretaceous of Madagascar; Mansourasaurus (Sallam et al 2018), Rukwatitan (Gorscak et al 2014), and Shingopana (Gorscak et al 2017) from the Late Cretaceous of Africa; Diamantinasaurus (Hocknull et al 2009, Poropat et al 2015, 2016) and Savannasaurus (Poropat et al 2016) from the Late Cretaceous of Australia, and Lohuecotitan (Díez Díaz et al 2016) from the Late Cretaceous of Europe. The distal forelimb is not well known in e20180374 2 | 42

Objectives

Findings

Discussion

Conclusion