Troodontidae is a clade of bird-like theropod dinosaur which have been allied, at various times, with nearly every major coelosaurian lineage.
Troodontid material were among the first dinosaur remains ever described. Initally, Leidy (1856) assumed they were lacertilian, but by 1924, they were refered to Dinosauria by Gilmore, who stressed obtensible ornithischian affinities. It was only in 1945 that C.M. Sternberg redefined Troodontidae as a theropod family. Since 1969, Troodontidae has typically been allied with Dromaeosauridae in a clade known as Deinonychosauria, but this was by no means a concensus. Hotlz (1996) erected Bullatosauria, uniting Ornithomimosauria and Troodontidae into a holophyletic clade on the basis of characters including, among others, an inflated parabasisphenoid and a long, low maxillary fenestra. The propubic pelvis also suggested they were less derived than dromaeosaurids.
