Osteology and phylogenetic relationships ofLigabuesaurus leanzai(Dinosauria: Sauropoda) from the Early Cretaceous of the Neuquén Basin, Patagonia, Argentina

Abstract

Osteological knowledge of the sauropod dinosaur Ligabuesaurus leanzai is increased by the description of new postcranial elements assigned to the holotype MCF-PVPH-233. Furthermore, a newly referred specimen, MCF-PVPH-228, is recognized after a detailed revision of the abundant sauropod material collected from the Lohan Cura Formation outcrops in the Cerro de los Leones locality (southern Neuquén Basin, Patagonia, Argentina). Recent laboratory preparation and fieldwork allowed us to recognize several new morphological features of the pectoral and pelvic girdles and the cervical and caudal anatomy. Thus, a new diagnosis of Ligabuesaurus is proposed that includes new autapomorphies and a unique combination of features. A phylogenetic analysis based on this new material recovers Ligabuesaurus as a non-titanosaurian somphospondylan, more derived than Sauroposeidon. Therefore, we discuss the palaeobiogeographical implications for the diversification and distribution of South American somphospondylans, especially in the Neuquén Basin, which are closely related to the early stages of evolution of Titanosauria. In this context, Ligabuesaurus represents one of the more complete Early Cretaceous Titanosauriformes and the earliest non-titanosaurian somphospondylan of South America. Finally, the new information on Ligabuesaurus contributes not only to reconstruction of the sauropod faunal composition of south-western Gondwana, but also sheds light on the early stages and emergence of titanosaurians.

Sauropod dinosaur teeth from the lower Upper Cretaceous Winton Formation of Queensland, Australia and the global record of early titanosauriforms

“…Similarly, they do not conform with the narrow-crowned tooth morphology displayed by nearly all post-Turonian titanosaurs (see below). Instead, the Winton Formation sauropod teeth most closely resemble those of the non-titanosaurian somphospondylan Ligabuesaurus leanzai [75,77], as well as the early branching titanosaurs Choconsaurus baileywillisi [84] and Sarmientosaurus musacchioi [85]. This implies that they pertain to either a non-titanosaurian somphospondylan, or to an early branching titanosaurian.…”

“…Albian-aged deposits in Argentina show some variation. Lower Albian deposits in Neuquén Province have yielded rebbachisaurids and non-titanosaurian somphospondylans including Ligabuesaurus [75,77,88,172–174], whereas upper Albian deposits in Chubut Province have produced the lognkosaurian titanosaur Patagotitan [175,176], but no rebbachisaurids. Rebbachisaurids are represented in the Albian–Cenomanian of Brazil [177], and dominate Cenomanian–Turonian sauropod faunas across Argentina [178–188].…”

Nuevos Restos De Rebaquisáuridos Desde La Formación Huincul (Cenomaniano Medio–turoniano Temprano) Del Centro De La Cuenca Neuquina, Patagonia, Argentina

“…For the osteological description, we followed the terminology used in Romer (1956), Wilson & Sereno (1998), Harris (2004), Upchurch et al (2004), andWilson (2006), and the terminology and abbreviations proposed by Wilson (1999Wilson ( , 2012 and Wilson et al (2011) for vertebral laminae and fossae. To assess the phylogenetic position of the specimens reported here, we carried out a cladistic analysis using a modified version of the data matrix of Bellardini et al (2022) (see NEXUS and TNT files in Online Supplementary Information). The data matrix was edited using Mesquite v.…”

“…In particular, analyzing the saurischian fossil record, a post-Turonian faunistic turnover can be recognized when mid-Cretaceous (Aptian-Turonian) faunas are compared with the post-Turonian ones (see Leanza et al, 2004;Candeiro et al, 2011;Novas et al, 2013;Candeiro, 2015;Krause et al, 2020;Ibiricu et al, 2020). Indeed, within Sauropoda, there is fossil evidence of Rebbachisauridae and both broad-toothed and narrow-toothed Titanosauriformes until the Cenomanian-Turonian interval (e.g., Canudo et al, 2018;Bellardini et al, 2022), whereas after the Turonian only the narrow-toothed titanosauriformes (all members of Titanosauria) represent the mega-herbivores saurischian fauna worldwide (e.g., Carballido et al, 2017). On the other hand, carcharodontosaurid and spinosaurid theropods were abundant until the early Late Cretaceous but disappeared after the Turonian.…”

A nearly complete skull of the sauropod dinosaurDiamantinasaurus matildaefrom the Upper Cretaceous Winton Formation of Australia and implications for the early evolution of titanosaurs

“…The teeth lack prominent mesial ( figure 20 d ) and distal ( figure 20 b ) carinae. Carinae characterize the teeth of most somphospondylans, although they are also absent in Ligabuesaurus [ 174 ], Sauroposeidon [ 175 ], and a small number of titanosaurs, including Rapetosaurus and Sarmientosaurus [ 41 , 101 , 152 ]. Based on the synchrotron scan data, the thickness of the tooth enamel is uniform labially and lingually.…”