The discovery of a giant predator in Patagonia provides exceptional testimony about the end of the age of dinosaurs. The unique position of a fossilized bone opens a window into its feeding habits.
This major find concerns a new theropod dinosaur, named
Joaquinraptor casali, which ruled the ecosystems of South America approximately 70 million years ago. Paleontologists have uncovered a partial but remarkably preserved skeleton, including elements of the skull, limbs, and vertebrae.
Reconstruction of the recently discovered megaraptor Joaquinraptor casali in Argentina with a Cretaceous-era crocodile arm in its mouth.
Illustration by Andrew McAfee, Carnegie Museum of Natural History
The most striking element is an ancient crocodilian humerus, found wedged between the jaws of the carnivore. This chance association offers a rare glimpse into the interactions between the large predators of this period.
A little-known predator from the Late Cretaceous
Joaquinraptor belongs to the enigmatic group of megaraptorids, theropods characterized by their imposing claws and considerable size. The specimen described in
Nature Communications is one of the most complete ever excavated for this lineage. Its analysis reveals an animal approximately seven meters long (about 23 feet), with a lightweight skull and relatively small teeth for a carnivore of this size. Its robust forelimbs ended in sickle-shaped claws, weapons likely used to grasp its prey.
This dinosaur lived in an environment of warm, humid floodplains in South America. At that time, tyrannosaurs dominated the northern hemisphere but were not present in this region. Megaraptorids like
Joaquinraptor therefore occupied the position of apex predators at the top of the food chain. They likely fed on herbivorous dinosaurs, such as young titanosaurs or hadrosaurs, which inhabited Patagonia at the time. Their evolutionary success lasted until the end of the Cretaceous.
The quality of the fossil's preservation allows scientists to estimate the individual's age at the time of its death. The study of bone microstructure indicates it was about 19 years old, probably sexually mature but not yet fully adult. This valuable information contributes to a better understanding of the biology and life cycle of these extinct animals. The discovery thus fills a significant gap in the fossil record of terminal Cretaceous theropods.
Lower jaws of Joaquinraptor (right and left dentaries) found in contact with an associated right crocodyliform humerus. The fossils were initially interlocked before being separated in the laboratory. Shown are the dentaries in lateral and medial views, and the humerus in posterior and anterior views. A fossilized meal with major implications
The presence of a crocodilian bone in the
Joaquinraptor's mouth raises an exciting question. Researchers seriously consider that it might be the remains of its last meal. The configuration of the bones, found in partial connection, rules out the hypothesis of a simple mixing of bones by aquatic currents after death. The association appears real and results from a behavioral event frozen in rock. Such cases of "fossilized behavior" are extremely rare.
If this interpretation is correct, it demonstrates that
Joaquinraptor attacked other predators of considerable size. The crocodilians of the time were not easy prey. This observation provides a direct clue about the diet and hunting strategies of this megaraptorid. It shows an ecosystem where interactions between large carnivores were common. This discovery goes beyond the simple anatomical description of a new species.
Studies are ongoing to confirm the nature of this association. Scientists must rule out any possibility of a taphonomic coincidence, a process that could have brought the bones together by chance. However, the absence of other foreign bones around the skeleton strengthens the meal hypothesis. This discovery paves the way for further analyses, such as searching for tooth marks on the crocodilian bone, which could definitively confirm the interpretation.
This exceptional fossil illustrates the diversity of morphologies and ecological strategies among large theropods. While the North American Tyrannosaurus rex primarily used its hyper-powerful jaw,
Joaquinraptor likely utilized its forelimbs armed with claws. These two lineages of apex predators thus developed distinct adaptations to occupy similar ecological niches, a fine example of evolutionary convergence.
Skeletal reconstruction of Joaquinraptor in left lateral view, with preserved bones indicated in blue. Illustrated are various cranial elements (maxilla, skull roof, braincase, postorbital, quadrate, mandibles), several vertebrae and ribs, as well as bones from the forelimbs and hindlimbs (scapulocoracoid, humerus, radius, ulna, phalanges, femur, tibia). Dotted lines mark missing areas. Cédric DEPOND