Joaquinraptor

MEANING: Joaquin thief

PERIOD: Late Cretaceous

CONTINENT: South America

Joaquinraptor is the most recent known megaraptoran. It was a large bipedal carnivore, growing to at least 7 m in length, and weighing approximately 1 t. Typical for megaraptorans, Joaquinraptor had a long lightly built skull with many relatively small teeth, and large slender claws on the first digit of each hand.

Abstract from paper: Recent fossil discoveries have cast considerable light on the palaeobiology of Megaraptora, a group of large-clawed carnivorous theropod dinosaurs known from Cretaceous deposits in Asia, Australia, and especially South America. Nevertheless, many important aspects of megaraptoran morphology and evolution remain poorly understood, due in large part to the fragmentary nature of most fossils of these theropods and the scarcity of anatomically overlapping skeletal elements among the known taxa. Here we report a previously unknown megaraptoran genus and species represented by a partially articulated partial skeleton recovered from an uppermost Cretaceous stratum of the Lago Colhué Huapi Formation of south-central Chubut Province in central Patagonia, Argentina. Pertaining to the derived megaraptoran subclade Megaraptoridae, the taxon is among the most completely represented and latest-surviving megaraptorans. Its stratigraphic occurrence indicates that these dinosaurs likely persisted to the Cretaceous/Palaeogene boundary; moreover, the preservation of a crocodyliform humerus between the dentaries of the new theropod may provide information on megaraptoran dietary preferences and feeding strategies. Megaraptorids appear to have been the apex predators in central and southern Patagonian palaeoecosystems approaching the end of the Cretaceous, in contrast to more northerly areas of South America where these niches were occupied by other non-avian theropod groups.

Joaquinraptor is from the Late Cretaceous. The Cretaceous is the third and final geological period of the Mesozoic Era, with the Late Cretaceous making up roughly the second half of it, lasting from about 100 to 66 million years ago. It was a time of significant evolutionary change, with dinosaurs reaching their greatest diversity before the mass extinction at the end of the Cretaceous.

The Cretaceous was a period with a relatively warm climate, though the Late Cretaceous experienced a global cooling trend, caused by falling levels of carbon dioxide in the atmosphere. The continents were nearing their present positions, but high sea levels flooded low-lying regions, turning Europe into an archipelago, and forming the Western Interior Seaway in North America. These seas were home to a variety of marine reptiles, including mosasaurs and plesiosaurs, while pterosaurs and birds shared the skies.

On land, dinosaurs continued to thrive and diversify during the Late Cretaceous, producing many of the most well-known groups, including tyrannosaurs, hadrosaurs, and pachycephalosaurs. Established Cretaceous dinosaur clades like the ceratopsians, ankylosaurs, and dromaeosaurs continued to flourish. Sauropod species consisted almost exclusively of titanosaurs, which seemed to be confined to the Southern Hemisphere for much of the Late Cretaceous. Flowering plants and grasses diversified and spread, becoming the dominant flora similar to what we see today.

The Cretaceous (along with the Mesozoic) ended with the Cretaceous–Paleogene (K–Pg) extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs, and large marine reptiles, died out. This event, likely triggered by an asteroid impact, is marked by the abrupt K–Pg boundary, a distinct geologic layer separating the Mesozoic and Cenozoic Eras. In its aftermath, mammals and avian dinosaurs rapidly diversified, becoming the dominant land animals of the Cenozoic Era.

Joaquinraptor is a megaraptoran. Megaraptora is a group of large predatory theropods that lived during the Cretaceous Period. They were most diverse in South America, but they had a widespread distribution. Despite their name, megaraptorans are not closely related to the smaller dromaeosaur “raptors”. Instead, they represent a distinct lineage of large-bodied predators that occupied apex roles in their ecosystems, though their exact phylogenetic affinities are not clear. Different studies place them among coelurosaurs, carnosaurs, or as a distinct branch within allosauroid theropods, reflecting ongoing uncertainty in their phylogenetic relationships.

The most distinctive feature of megaraptorans is the enlarged, recurved claws on their forelimbs, which in some species exceeded 30 centimeters in length. These claws, combined with long, powerful arms and lightly built skeletons, suggest they were agile hunters that relied heavily on grasping and slashing during predation. Their skulls were relatively lightly built compared to other large theropods, and they likely used their forelimbs as their primary weapons. Fossil evidence indicates they persisted into the Late Cretaceous, making them some of the last surviving large predatory dinosaurs in the Southern Hemisphere.