Deinonychosauria

Deinonychosauria is a clade of paravian theropod dinosaurs that historically includes the two main families Dromaeosauridae (the so‑called raptors) and Troodontidae (the troodontids). In many phylogenetic definitions the group is the closest non-avian relative of birds, excluding Avialae, while some authors define Deinonychosauria as all taxa more closely related to Deinonychus than to birds. Because of differing definitions, the exact composition of the clade varies among studies, but it is generally treated as a close sister group to birds within Paraves.

Members of Deinonychosauria are characterized by features that suggest an agile, grasping predatory lifestyle. They typically show well-developed forelimbs, often with lengths and joints suited to grasping, and a distinctive second toe bearing a curved, sickle-shaped claw in many dromaeosaurids. For several troodontids and dromaeosaurids, remains indicate streamlined bodies and evidence of feathers, reinforcing the view that feathered theropods were common in this lineage. The degree and placement of certain skeletal traits can vary, contributing to debates about exact relationships within the group.

Geographically and temporally, deinonychosaurs are known from several continents, with fossils reported in Asia, North America, and Europe. Notable genera include Velociraptor, Deinonychus, and Utahraptor among dromaeosaurids, and Troodon and Zanabazar among troodontids. Their proximity to birds has made Deinonychosauria central to discussions of how flight and other avian features evolved in theropods.

Overall, deinonychosaurs illuminate key steps in paravian evolution, illustrating the transition from ground-dwelling predators toward the flight-adapted lineage leading to birds.