Was this bizarre Mongolian dinosaur a swimmer, or just a misunderstood land-dweller?

Nature · Published 3 October 2026 Swipe more like this →

In short: Halszkaraptor escuilliei, a small dinosaur from Mongolia, was initially hailed as the first known semiaquatic, fish-eating non-avian dinosaur. Its strange, duck-like anatomy sparked a scientific debate that challenges how we interpret the evolution of bird-like dinosaurs. New research suggests its supposed aquatic adaptations might be common traits among its ancestors.

Discovered in the Late Cretaceous deposits of Mongolia, Halszkaraptor escuilliei was first described in 2017 by a team including Andrea Cau. The specimen, a subadult roughly the size of a mallard duck, possesses a striking array of features: a flattened snout, an exceptionally long neck, and forearms with unusual proportions. These characteristics led initial researchers to propose that the creature occupied a semiaquatic niche, hunting fish in a manner similar to modern crocodylians or aquatic birds.

The core of the aquatic hypothesis rested on the dinosaur's rostral neurovascular system—a complex network of canals in the premaxilla. While such systems are common in modern piscivores, critics argue that these features are widespread across various maniraptoran dinosaurs, including terrestrial theropods. By comparing Halszkaraptor to other maniraptorans, such as the basal therizinosaur Jianchangosaurus, researchers have found that these neurovascular foramina appear on the dorsal surfaces of the premaxillae in many non-aquatic species, suggesting they are not exclusive indicators of a water-based lifestyle.

Rather than a specialized swimmer, Halszkaraptor is now increasingly viewed as a critical evolutionary link. It belongs to the Halszkaraptorinae, a clade at the base of the Dromaeosauridae. Its anatomy represents a mosaic of plesiomorphic, derived, and transitional features that bridge the gap between basal maniraptorans and the specialized, hypercarnivorous dromaeosaurids. This reevaluation suggests that the bizarre traits once used to argue for piscivory are likely ancestral characteristics of the broader maniraptoran lineage, rather than evidence of a unique ecological shift into the water.

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