Giants and Bizarres: Body Size of Some Southern South American Cretaceous Dinosaurs

Body masses of some South American dinosaurs are estimated. The sauropod Argentinosaurus huinculensis reached 73 tonnes, and therefore, is the largest of all land animals whose mass has been rigorously obtained. Another sauropod, Antarctosaurus giganteus, was the second largest, at nearly 69 tonnes, while Antarctosaurus wichmannianus reached 34 tonnes. A third sauropod, the bizarre-looking Amargasaurus cazaui, was much smaller, with a body mass of only 2.5 tonnes. Among theropods, the body mass of the strangely looking, horned Carnotaurus sastrei, was volumetrically estimated at 1.5 tonnes, while allometric equations on limb measurements yielded overestimations. Moreover, the holotype specimen of Giganotosaurus carolinii (MUCPv-CH-1) was about as large as the average-sized Tyrannosaurus rex, and only marginally smaller than “Sue”, the largest specimen. However, a new dentary of Giganotosaurus (MUCPv-95) is 8% longer than that of the holotype. Assuming geometric similarity, that individual must have had a body mass above 8 tonnes and hence must have been the largest theropod ever found.