troodontids

Troodontidae is a family of small to medium-sized, bird-like theropod dinosaurs within the clade Paraves. They are part of Deinonychosauria, a group that also includes the dromaeosaurids, and are among the closest non-avian relatives of birds. The group is primarily known from the Late Jurassic to the Late Cretaceous, with fossils found in Asia and North America. The type genus is Troodon, from which the family takes its name.

Anatomy and distinguishing features: Troodontids tended to be small to medium in size, with relatively long hind limbs and a proportionally large skull. They show a comparatively large braincase relative to body size, suggesting advanced sensory and cognitive abilities for a theropod. Teeth are generally sharp and finely serrated, suitable for a carnivorous diet, and the hands have three functional fingers. The feet often carried a curved second toe claw, a trait shared with other deinonychosaurs, though the exact development of this feature varies among genera.

Paleobiology: Troodontids are interpreted as carnivores, and possibly omnivorous in some cases. They likely hunted small vertebrates and invertebrates, using keen vision and agile locomotion to capture prey. Their brain size and sensory adaptations imply sophisticated behavior for a theropod, though direct evidence of social behavior remains limited.

Distribution and fossil record: Notable troodontids have been described from North America (including Troodon and related taxa) and Asia (such as Saurornithoides, Sinornithoides, and Zanabazar). They appear most prominently in Late Cretaceous deposits, with earlier records known from Asian assemblages.

Phylogeny: Within Paraves, troodontids form the family Troodontidae and are grouped with the dromaeosaurids in Deinonychosauria. They are considered close relatives of birds, sharing several derived features, but are not regarded as direct ancestors of modern birds.