Meraxes gigas. Image credit: J. Gonzalez
The Cretaceous beds of Patagonia have yielded the most comprehensive record of Cretaceous non-avian theropods from Southern Hemisphere, which includes at least five main theropod lineages: Abelisauroidea, Carcharodontosauridae, Megaraptora, Alvarezsauridae, and Unenlagiidae. These record facilitates the understanding of the origin, evolution, and radiation of theropods from Gondwana. The first remains of dinosaurs were found near Neuquen city by an officer army in 1882 and were sent to Florentino Ameghino, the “founder father” of Argentinian paleontology.
Carcharodontosauridae includes the largest land predators in the early and middle Cretaceous of Gondwana, like the popular, Giganotosaurus carolinii. Members of this theropod family were first recorded in Cenomanian beds of Africa. The group possess widely fenestrated skulls, and in some cases with heavily sculptured facial bones. Another common trait is the fusion of cranial bones. Meraxes gigas, a new specimen from the Upper Cretaceous of northern Patagonia, Argentina, is the most complete carcharodontosaurid ever found and provides new information about the skull length in Giganotosaurus.
Reconstruction of the skeleton of Meraxes. From Canale et al., 2022
The holotype (MMCh-PV 65) is represented by a nearly complete skull without mandibles, pectoral and pelvic girdles, fore- and hindlimbs, fragments of cervical and dorsal vertebrae, complete sacrum, and proximal and middle caudal vertebral series. The first remains were discovered in 2012 in the Upper Cretaceous Huincul Formation of northern Patagonia, Argentina. The new specimen weighed more than 4 tons and measured up to 11 meters (36 feet) long. Histological analysis indicates that this dinosaur was an adult of 45-53 years of age at death.
The name comes from Meraxes, a dragon of the Song of Ice and Fire saga (by George R.R. Martin), with golden eyes and silver scales, named for a god of the Valyrian Freehold. The specific name “gigas” (gigant in Greek) makes reference to the size of the species.
Skull of Meraxes. Image credit: Fundación Azara
The skull of Meraxes is profusely ornamented and has a total length of 127 cm. This is the most complete cranium of any Carcharodontosaurinae. Applying scaling equations and measurements taken from Meraxes, the team lead by Dr. Juan Canale from the Museo Paleontológico Ernesto Bachmann, has estimated the size of the Giganotosaurus skull. The results indicate a length of 163 cm, one of the biggest theropod skulls ever found.
Meraxes also preserves near-complete forelimbs which are about half the length of the femur, a feature comparable to late tyrannosaurids and abelisaurids. This reveals a trend towards forelimb reduction in megapredatory theropod. Quantitative analyses suggest that this evolutionary convergence is especially pronounced between forelimb ratios of Meraxes and the tyrannosauroid Tarbosaurus.
References:
Canale, J.I. et al., New giant carnivorous dinosaur reveals convergent evolutionary trends in theropod arm reduction. Current Biology (2022). doi:10.1016/j.cub.2022.05.057
Novas, F.E., et al., Evolution of the carnivorous dinosaurs during the Cretaceous: The evidence from Patagonia, Cretaceous Research (2013), http://dx.doi.org/10.1016/j.cretres.2013.04.001
Letters from Gondwana. 