A recently discovered fossil in Argentina has unveiled a new species of carnivorous dinosaur, shedding light on a lesser-known category of Cretaceous Period predators. This significant find is marked by the dinosaur’s intact skull and an astonishing detail: it was found with a crocodile leg firmly gripped in its jaws.
Details of the Discovery
Named Joaquinraptor casali, this dinosaur roamed the Earth approximately 67 million years ago in what is now central Patagonia. Measuring around 23 feet in length and weighing about one ton, its remains suggest it may have perished while attempting to devour a large relative of crocodiles.
According to scientists, the presence of the crocodile leg raises intriguing possibilities about the circumstances of its death, hinting that it might have choked while feeding.
Understanding Joaquinraptor
The Joaquinraptor (pronounced wah-KEEN-rap-tor) is classified as a member of the megaraptorans, a group of carnivorous dinosaurs that inhabited South America, Asia, and Australia. These dinosaurs are characterized by their long arms and large, sharp claws on three fingers, as well as their elongated skulls, which are notably lighter built compared to those of other large predators.
“Megaraptorans are among the least understood dinosaurs of all,”
— Lucio Ibiricu, Instituto Patagónico de Geología y Paleontología
Paleontologist Lucio Ibiricu, the study’s lead author, points out that despite the early members of this lineage dating back 130 million years, much about them has remained a mystery. The findings from Joaquinraptor reveal that these dinosaurs thrived well into the end of the Cretaceous, which came to a close about 66 million years ago due to an asteroid impact.
Significance of the Findings
Ibiricu emphasized that previous fossils of megaraptorans were often incomplete, hindering comprehension of their anatomy, habits, diet, and evolutionary significance. The well-preserved skull of Joaquinraptor provides important insights into its physical structure, and the crocodile leg found in its mouth may offer clues about its dietary patterns.
The humerus, or upper forelimb bone, of the crocodile found in the dinosaur’s jaws suggests that Joaquinraptor might have been consuming a formidable predator when it met its fate.
Location and Preservation
The remains were unearthed in 2019 at the Rio Chico’s headwaters near Lago Colhué Huapi in Chubut Province. The discovery site and the dinosaur itself were named in honor of Ibiricu’s son, Joaquin.
The fossil comprises a substantial portion of the dinosaur’s skull, shoulder girdle, forelimb, hind limb, and various other bones, including ribs and vertebrae. Notably, the preserved sickle-shaped claw on the middle finger stands out, although the claws from the other two fingers were not found.
“It is among the most complete megaraptoran skeletons yet known to science,”
— Matt Lamanna, Carnegie Museum of Natural History
Co-author Matt Lamanna from the Carnegie Museum of Natural History noted the exceptional completeness of the fossil. An analysis of the rib and leg bones indicates that the Joaquinraptor was likely around 19 years old at the time of its death, in a stage of life that was probably sexually mature but possibly not fully grown.
Ecological Role
The skull’s dimensions span approximately 24 to 28 inches, lined with small, sharp curved teeth typical for a dinosaur of its size. Despite its smaller teeth, Joaquinraptor was a dominant predator, likely positioned at the top of the food chain within its warm, humid coastal environment.
In addition to the possible crocodile prey, the researchers hypothesize that Joaquinraptor may have hunted various herbivorous dinosaurs, including young titanosaurs and duck-billed hadrosaurs that inhabited the region.
Comparative Analysis with Other Predators
When juxtaposed with the iconic Tyrannosaurus, which thrived in western North America during the same era, the differences in anatomy are stark. The T. rex is known for its massive skull, formidable teeth, and disproportionately small arms, while Joaquinraptor possessed long arms and sharp hands suited for capturing prey.
This suggests that these two predatory dinosaur lineages evolved different adaptations to accomplish basically the same thing — that is, to capture, subdue, kill and eat other animals such as other dinosaurs.
— Matt Lamanna
Lamanna concluded that the evolution of these different predatory strategies raises intriguing questions about the ecological dynamics of the Cretaceous period and indicates that there were multiple pathways to becoming a top predator.
