Anatomy of the basal titanosaur (Dinosauria, Sauropoda) Andesaurus delgadoi from the mid-Cretaceous (Albian-early Cenomanian) Río Limay Formation, Neuquén Province, Argentina: implications for titanosaur systematics

Abstract

Titanosauria is a taxonomically and morphologically diverse clade of sauropod dinosaurs that appeared in the Middle Jurassic and radiated in the mid-Late Cretaceous; however, its intrarelationships are poorly understood. The mid-Cretaceous Argentinean sauropod Andesaurus delgadoi has repeatedly been recovered at the base of Titanosauria, and thus represents a crucial taxon for determining the evolutionary history of this clade; yet it has only received a brief description. Here, we re-describe the holotype, comprising dorsal, sacral, and caudal vertebrae, as well as limb and pelvic elements. Detailed comparisons are made with a global array of titanosauriforms. Andesaurus is a valid genus and can be diagnosed by five autapomorphies: (1) posterior dorsal neural spine height greater than twice centrum height (autapomorphic within Macronaria); (2) square-shaped anterior-middle caudal centra in lateral view; (3) anteroposteriorly elongate fossa present on the anterodorsal corner of the lateral surface of middle-posterior caudal centra; (4) ridge along the midshaft of the ventral surface of metacarpal I, close to the ventromedial margin; (5) prominent ventromedial ridge along the distal half of metacarpal V. Other remains previously attributed to Andesaurus cannot be referred to this genus. Sixteen putative titanosaur synapomorphies can be recognized in Andesaurus, including: (1) lateral pneumatic foramina in dorsal vertebrae situated within fossae; (2) anterior-middle caudal vertebrae with ventrolateral ridges either side of a ventral midline hollow; and (3) lateral bowing of metacarpal I. This revision provides an important foundation for future phylogenetic analyses of titanosaurs, and adds to our growing understanding of this enigmatic clade. Lastly, we recommend the disuse of the coordinated suprageneric rank taxa of Andesaurus (Andesaurinae, Andesauridae, and Andesauroidea), at least until titanosaur intrarelationships are better elucidated.

A Gigantic, Exceptionally Complete Titanosaurian Sauropod Dinosaur from Southern Patagonia, Argentina

“…7, 14). Anterior caudal centra are pierced by small vascular foramina ventral to the transverse processes, as in Adamantisaurus 26, Alamosaurus 27, Andesaurus 28, Paralititan 7, Pellegrinisaurus 29, and other sauropods30. Their neural spines are distinctive in possessing hypertrophied prespinal and postspinal laminae (presumably indicative of robust interspinal ligament attachments) and deep, extensively subdivided pneumatocoels between the spinoprezygapophyseal and spinopostzygapophyseal laminae (occupying the position of the conjoined postzygapophyseal spinodiapophyseal and postzygapophyseal centrodiapophyseal fossae of Wilson et al31).…”

Appendicular osteology ofDreadnoughtus schrani, a giant titanosaurian (Sauropoda, Titanosauria) from the Upper Cretaceous of Patagonia, Argentina

“…Mannion and Calvo (2011) suggest that the presence of an oval (rather than subcircular) obturator foramen in the pubis (like the one that Lirainosaurus astibiae presents), with the long axis oriented in the same plane as the long axis of the pubic shaft, might be a titanosauriform characteristic. Like somphospondylans, L. astibiae has a scapular glenoid surface that is strongly bevelled medially, and the proximal end of the humerus is flat in anterior view (Wilson and Sereno, 1998;Wilson, 2002).…”

Osteology of Huabeisaurus allocotus (Sauropoda: Titanosauriformes) from the Upper Cretaceous of China

“…In the 13 years since the original description of Huabeisaurus , 17 new sauropod species have been erected from the Cretaceous of East Asia (see lists in [1], [2]). Many authors have noted similarities among Cretaceous East Asian sauropods, often suggesting that several of these taxa belong to a clade grounded on a genus with well-known anatomy (e.g., Nemegtosauridae, [3]–[5]; Opisthocoelicaudinae, [6]; Euhelopodidae, [2], [7]; see [8] for further discussion).…”