Barsbold, 1983 Saurornithoididae: Barsbold, 1974:
Diagnosis . Small to moderately large coelurosaurs. Skull small, with elongated facial region, highly extended antorbital fenestrae, basisphenoid capsule, and osseous middle ear region. Elongate, large maxillary fenestrae. Posterior part of external nares limited by the maxilla. Jugal slightly widened from the deviation of the posterior process. Small teeth, close together, predominately with posterior serrations. Caudal vertebrae lack ossified tendons. Pes with reversed digit II.
Composition . One genus – Saurornithoides Osborn, 1924.
Comparisons . Elongate skull with extended accessory antorbital fenestra and reversed pedal digit differentiate saurornithoidids from the similar coelurids and other coelurosaur families.
Discussion . The systematic position of saurornithoidids has remained unclear for some time. They have been supposed to fall with dromaeosaurids, and identified as an independent subfamily within them (Colbert and Russell, 1969; Osborn, 1969a, 1976a), and also classified with Troodontidae (Russell, 1948, 1969). However, the prepubic structure of the saurornithoidid pelvis clearly differentiates them from dromaeosaurids, which also have a pes with a reversed digit II (Barsbold, 1976a). The family Troodontidae, based on highly insufficient material (typical specimens include single teeth, distinct from the teeth of saurornithoidids; see Leidy, 1856), occupies an undefined (if valid at all) systematic position.
Diagnosis . Small to moderately large coelurosaurs. Skull small, with elongated facial region, highly extended antorbital fenestrae, basisphenoid capsule, and osseous middle ear region. Elongate, large maxillary fenestrae. Posterior part of external nares limited by the maxilla. Jugal slightly widened from the deviation of the posterior process. Small teeth, close together, predominately with posterior serrations. Caudal vertebrae lack ossified tendons. Pes with reversed digit II.
Composition . One genus – Saurornithoides Osborn, 1924.
Comparisons . Elongate skull with extended accessory antorbital fenestra and reversed pedal digit differentiate saurornithoidids from the similar coelurids and other coelurosaur families.
Discussion . The systematic position of saurornithoidids has remained unclear for some time. They have been supposed to fall with dromaeosaurids, and identified as an independent subfamily within them (Colbert and Russell, 1969; Osborn, 1969a, 1976a), and also classified with Troodontidae (Russell, 1948, 1969). However, the prepubic structure of the saurornithoidid pelvis clearly differentiates them from dromaeosaurids, which also have a pes with a reversed digit II (Barsbold, 1976a). The family Troodontidae, based on highly insufficient material (typical specimens include single teeth, distinct from the teeth of saurornithoidids; see Leidy, 1856), occupies an undefined (if valid at all) systematic position.