A monoespecific early ontogenetic stage sauropod titanosaurs bonebed, from La Invernada site (Bajo de la Carpa Formation, Santonian) from North Patagonia

FILIPPI, L.S.; BARRIOS, F.; PAULINA-CARABAJAL, A.; FARÍAS-KLEPP, M.; CÁRDENAS, M.; GIANECHINI, F.A.; VETTORAZZI, L.A.; VALDÉZ, H.; RODRÍQUEZ-CANALIS, C.; MÉNDEZ, A.H.; SECULI-PEREYRA, E.; GONZÁLEZ-DIONIS, J.; GARRIDO, A.C.; HEREDIA, A.M.; LEE, Y.-N.; KWON, K.-D.

San Luis

Jornada; XXXVIII Jornadas Argentinas de Paleontología de Vertebrados; 2025

Comisión Organizadora XXXVIII Jornadas Argentinas de Paleontología de Vertebrados

The bonebed from the La Invernada locality, found in 2024, composed of axial and appendicular elements of early ontogenetic stage sauropod titanosaurs (MAU-Pv LI-733-734-735), provides new materials in recent fieldwork. Among the most abundant complete appendicular elements, there are humerus, radii and tibiae, that show differences in sizes. So far, four humerus have been collected, two left and two right (lengths 27, 29, 38.5 and ~60 cm), four radii, two left and two right (lengths 19 and 22.5 cm), and six tibiae, one left and five right (lengths 19.5, 20, 21.5, 22.2, 24 and 26.2 cm). Although the elements are still covered by sediment, its anatomical features can be observed. The humerus present a robust index (RI= 0.27-0.3) as in Patagotitan (RI=0.28), Rapetosaurus (RI=0.29), and Neuquensaurus (RI=0.3). The humeral head presents a dome-like shape, situated close to the mid length, near the proximomedial border. The dorsal surface of the proximal end presents a convex medial portion and a flat lateral one, as in other titanosauriforms (e.g., Chubutisaurus, Diamantinasaurus, Opisthocoelicaudia, Epachthosaurus, Petrobrasaurus, Narambuenatitan, Patagotitan). The deltopectoral crest is low and relatively narrow throughout its length. The lateral margin of the humerus is straight at the level of the midshaft, and the medial margin presents a proximodistal concavity, as in most titanosauriforms. Distally, the radial and ulnar condyles are undivided. The radius robustness index is relatively low (0.23), similar to Chubutisaurus (0.22), Mendozasaurus (0.20), and Rapetosaurus (0.19). The proximal end is oval, mediolaterally expanded, and anteroposteriorly short, almost perpendicular to the proximodistal axis, with a torsion relative to the distal axis. The distal end is elliptical, with the major axis lateromedially oriented. On the posterior face, a short interosseous ridge is observed, as in other titanosaurs (e.g., Rapetosaurus, Mendozasaurus, Bonitasaura, Neuquensaurus). The tibia exhibits a tendency towards robustness (RI=0.25 – 0.29). The proximal end is anteroposteriorly longer than mediolaterally wide. The cnemial crest is well-developed, anterolaterally oriented, and presents a circular outline in lateral view. The diaphysis is elongated anteroposteriorly and flattened mediolaterally. The distal end is mediolaterally expanded, and the posterior process is reduced. The articular surface for the ascending process of the astragalus is well-developed. The observations made show a similar anatomical characteristic between the elements, confirming the hypothesis of a monospecific site. A future histological analysis of these appendicular elements would allow us to infer the ontogenetic stages of the individuals and expand the knowledge about early stages of titanosaur sauropod development.