A new dinosaur tracksite from the Allen Formation (Upper Cretaceous), Área Natural Protegida Paso Córdoba, Río Negro Province, Argentina

FISCHER, GERALDINE; HEREDIA, ARTURO M.; CAVASIN, SOL; DÍAZ-MARTÍNEZ, IGNACIO; DE VALAIS, SILVINA

Senillosa

Jornada; V Jornadas de Paleontología de la Cuenca Neuquina; 2025

Comisión Organizadora V Jornadas de Paleontología de la Cuenca Neuquina

Approximately 200 true and transmitted tracks are preserved across six fine-grained sandstone layers (50 cm thick) at Barbieri site, Allen Formation (upper Campanian–lower Maastrichtian, Neuquén Basin), within the Área Natural Protegida Paso Córdoba, 15 km from General Roca, Río Negro, Argentina. The main track-bearing surface contains about 100 manus and pes imprints, including two quadrupedal trackways preserved as natural casts. Manus prints are crescent-shaped with concave posterior margins, while pes prints are mostly subcircular, some showing V-shaped posterior margins and a lateral notch. The longest trackway consists of 14 sets. Manus prints average 23.1 × 28.4 cm and pes prints 37.5 × 29.8 cm. It shows moderate heteropody (59%), narrow to intermediate gauge (WAP/PL: 0.56; PTR: 47%), an internal width of 4–6 cm, and stride length (SL) of 125–131 cm. Estimated hip height is 150–160 cm. Assuming a trotting gait (SL/PL: 2.01), glenoacetabular distance (GAD) is 98 cm, limb phase 29%, and speed approximately 2.56 km/h, SE–NW direction. The second trackway has three sets, with manus and pes prints averaging 19.2 × 20.2 cm and 24.5 × 29.8 cm, respectively, and higher heteropody (71%). Its gauge is similar (WAP/PL: 0.61; PTR: 43.5%), with an internal width of 5–8 cm, and stride length of 101 cm. Estimated hip height is 94–112 cm. Assuming a fast-walking gait (SL/PL: 1.98), GAD is 81 cm, limb phase 25%, and speed approximately 2.77 km/h, WNW–ESE direction. Morphology, stratigraphic context, and spatial distribution support a titanosaurian affinity, likely representing individuals of different sizes and/or ontogenetic stages. Despite differences in body size and stride length, similar speeds and limb phase values suggest the smaller individual compensated by increasing limb cycling frequency. This record offers new insights into sauropod locomotion during the Late Cretaceous of Patagonia.