Joaquinraptor casali

Joaquinraptor casali was a large, derived megaraptorid theropod dinosaur that lived in what is now Chubut Province, Argentina, during the Late Cretaceous period, approximately 72–66 million years ago (Maastrichtian stage). It was discovered in the Lago Colhué Huapi Formation, a sedimentary deposit known for its fluvial and lacustrine facies.

The name Joaquinraptor honors Joaquín Casali, a volunteer who aided in the discovery, while casali is for him.

As a member of Megaraptoridae within Megaraptora, Joaquinraptor was an apex predator in southern Patagonia, persisting to the K/Pg boundary.

Etymology

The genus name “Joaquinraptor” combines “Joaquín,” honoring volunteer Joaquín Casali, and Latin “raptor,” meaning “thief.” The species name “casali” also honors him.

Physical Characteristics

Joaquinraptor casali was a large megaraptoran, estimated at least 6-7 m (19-23 ft) in length. The holotype is a partially articulated skeleton, more complete than many megaraptorans.

Key anatomical features include:

• Elongate skull with low-crowned teeth and extensively pneumatized bones.
• Powerfully developed forelimbs with hypertrophied unguals on digits I and II.
• Partial skeleton including vertebrae, skull bones, forelimbs, hindlimbs, pectoral girdle.
• Preservation of a crocodyliform humerus between dentaries, suggesting dietary preferences.

These traits indicate a coelurosaurian theropod adapted for predation.

Diet and Feeding Habits

As a carnivorous theropod, Joaquinraptor casali preyed on various vertebrates. Its diet likely included:

• Crocodyliforms, as evidenced by preserved humerus in jaws.
• Smaller dinosaurs and reptiles in Patagonian ecosystems.
• Scavenging opportunities in fluvial environments.

It used powerful forelimbs and claws for grasping prey.

Habitat and Distribution

Joaquinraptor casali lived in south-central Chubut Province, Argentina, in the Lago Colhué Huapi Formation.

Its environment was characterized by:

• Fluvial sandstones and lacustrine mudstones.
• Humid, subtropical climate near the end-Cretaceous.
• Diverse fauna, with megaraptorids as apex predators in southern Patagonia.

The formation yields latest Cretaceous fossils.

Paleoenvironment

The site was a floodplain ecosystem during the Maastrichtian, with rivers and lakes supporting rich biodiversity. The assemblage reflects a southern Patagonian niche dominated by megaraptorans.

Behavior and Social Structure

No direct evidence, but megaraptorans likely were solitary hunters. Possible behaviors include:

• Ambush predation using strong forelimbs.
• Territoriality in resource-rich floodplains.
• Potential scavenging, given opportunistic feeding.

As an apex predator, it dominated its niche.

Discovery and Research

The holotype was discovered in the Lago Colhué Huapi Formation. Described in 2025, it includes crocodyliform remains, informing paleoecology.

Phylogenetic analysis places it in Megaraptoridae, sister to Megaraptor + others.

Discovery Context

Found in uppermost Cretaceous strata, the skeleton was partially articulated, dating to near the K/Pg boundary.

Significance and Interesting Facts

• Youngest definitive megaraptoran, persisting to K/Pg.
• Most complete latest Cretaceous megaraptoran skeleton.
• Evidence of crocodyliform predation.
• Apex predator in southern Patagonia, contrasting northern abelisaurids.
• Highlights megaraptoran evolution as coelurosaurs.

Conclusion

Joaquinraptor casali was a large megaraptorid from the Late Cretaceous of Argentina, exemplifying the clade’s persistence and role as apex predators. Its discovery sheds light on paleoecology near the K/Pg. This 2025 find enhances understanding of Gondwanan theropods.