A new member of the megaraptoran dinosaur family has been discovered by a team of paleontologists from Argentina and the United States.
Joaquinraptor casali. Image credit: Andrew McAfee, Carnegie Museum of Natural History.
The new dinosaur species lived in what is now Patagonia, Argentina, during the latest part of the Cretaceous period, between 70 and 67 million years ago.
Dubbed Joaquinraptor casali, the ancient predator was a top predator in the region.
It belonged to Megaraptora, a group of large-clawed carnivorous theropod dinosaurs known from Cretaceous deposits in Asia, Australia, and especially South America.
“Megaraptorans were carnivorous theropod dinosaurs with elongated skulls and powerful forearms with large claws found across Asia, Australia and South America,” said Dr. Lucio Ibiricu, a paleontologist at the Instituto Patagónico de Geología y Paleontología and the Universidad Nacional de la Patagonia San Juan Bosco, and colleagues.
“However, our understanding of this group is hindered by the lack of complete fossils.”
A well-preserved and partially articulated skeleton of a single Joaquinraptor casali individual was found in the Lago Colhué Huapi Formation of south-central Chubut Province in central Patagonia, Argentina.
The specimen included much of the dinosaur’s skull, fore and hind-limbs, ribs and vertebrae.
Based on the bone microstructure, the paleontologists suggest that the specimen is an adult, but possibly not fully grown.
Extrapolating from other megaraptoran remains, they estimate that Joaquinraptor casali may have been around 7 m in length and weighed more than 1,000 kg.
Sedimentary evidence indicates that this dinosaur lived in a warm, humid floodplain environment.
“The presence of a fossilized crocodile leg bone pressed against the lower jaws of Joaquinraptor casali gives hints about its feeding behavior and suggests it may have been an apex predator in the region,” the researchers said.
“However, more research is needed to provide further insights into its behavior and ecological role.”
According to the scientists, Joaquinraptor casali and other megaraptorans survived as the dominant predators in this region of South America before going extinct at the end of the Cretaceous with other non-avian dinosaurs.
“South American megaraptorids appear to have attained larger body sizes (7 m or greater in total body length) than their generally more ancient relatives from Australia (5-6 m),” they said.
“Patagonian megaraptorids may have continued to increase in size through the remainder of their evolutionary history — perhaps spurred at least in part by the extinction of carcharodontosaurids during the Turonian — with some latest Cretaceous forms potentially reaching body lengths of 9 m or more.”
“Among other benefits, this may have allowed megaraptorids to occupy the apex predator niches in their respective habitats.”
“Moreover, and as evidenced by the Maastrichtian (probably Late Maastrichtian) stratigraphic occurrence of Joaquinraptor casali, these theropods may well have survived to the Cretaceous-Paleogene boundary, only to ultimately perish alongside all other non-avian dinosaurs.”
The discovery of Joaquinraptor casali is described in a paper published in the journal Nature Communications.
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L.M. Ibiricu et al. 2025. Latest Cretaceous megaraptorid theropod dinosaur sheds light on megaraptoran evolution and palaeobiology. Nat Commun 16, 8298; doi: 10.1038/s41467-025-63793-5
