Chucarosaurus diripienda. Image credit: Sebastián Rozadilla.
The Argentinean record of titanosaurs is particularly abundant. The study of this diverse group of sauropod dinosaurs embrace an extensive list of important contributions, which started with Richard Lydekker’s pioneering work on Patagonian dinosaurs. Some of them, were the largest animals to ever walk the Earth: Argentinosaurus, Futalognkosaurus, and Puertasaurus surpassed lengths of 37 m and masses of 70 tons. The best preserved skeletal elements in South American sauropodomorphs are axial and appendicular one, because distinct factors have limited the preservation of complete and articulated skeletons when the specimens are more than 10 m long.
Discovered in the Upper Cretaceous strata of the Huincul Formation, Chucarosaurus diripienda is the biggest dinosaur found in Rio Negro province. The holotype (MPCA PV 820) includes a complete left humerus, left radius, left complete metacarpal II, left ischium, left femur, left fibular shaft, proximal of right tibia. and distal end of indeterminate metapodial. The femur was roughly 1.9 metres (6.2 ft) long. The humerus is slightly twisted and relatively slender.
Left humerus of Chucarosaurus diripienda (holotype, MPCA PV 820). Scale bar: 20 cm. From Angolin et al., 2023.
The generic name is derived from the Quechua word Chucaro, meaning hard and indomitable animal; and saurus, a Latin word for reptile. The specific name, diripienda, derived from the Latin, meaning scrambled.
Chucarosaurus lived about 90 million years ago. The body length estimated is ∼ 30 m (98 ft) long. Body mass estimated suggests that Chucarosaurus weighted 40-50 tons. Phylogenetic analysis recovered Chucarosaurus within the Colossosauria clade. The new specimen resembles Mendozasaurus in having relatively gracile humerus and femur (the forelimb was shorter than the hindlimb, with a humerus 78% the length of the femur). The deltopectoral crest of the humerus was thickened in its distal half. Additionally, the ischium has a shorter, more robust iliac peduncle than in other titanosaurs.
References:
F.L. Agnolin et al. A new gigant titanosaur (Dinosauria, Sauropoda) from the Upper Cretaceous of Northwestern Patagonia, Argentina. Cretaceous Research, published online February 2, 2023; doi: 10.1016/j.cretres.2023.105487
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