Troodontidae

Automatic taxobox | name = Troodontids | fossil_range = Middle Jurassic–Late Cretaceous, | image_caption = Collection of four troodontids, clockwise from top left: Mei, unnamed Alaskan troodontid, Jianianhualong, Sinovenator. | image = Troodontidae.jpg | taxon = Troodontidae | authority = Gilmore, 1924 | type_species = Troodon formosus | type_species_authority = Leidy, 1856 | subdivision_ranks = Clade | subdivision = *Albertavenator Almas Archaeornithoides? Geminiraptor Hesperornithoides Jianianhualong Koparion? Liaoningvenator Paronychodon? Papiliovenator Polyodontosaurus Sinornithoides Talos Tochisaurus Xixiasaurus Jinfengopteryginae Sinovenatorinae Troodontinae | synonyms = *Saurornithoididae Barsbold, 1974 Troodontidae tro:.@'dQntᵻdi: is a clade of bird-like theropod dinosaurs. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinosaurian lineages. More recent fossil discoveries of complete and articulated specimens (including specimens which preserve feathers, eggs, embryos, and complete juveniles), have helped to increase understanding about this group. Anatomical studies, particularly studies of the most primitive troodontids, like Sinovenator, demonstrate striking anatomical similarities with Archaeopteryx and primitive dromaeosaurids, and demonstrate that they are relatives comprising a clade called Paraves. Troodontids are a group of small, bird-like, gracile maniraptorans. All troodontids have unique features of the skull, such as large numbers of closely spaced teeth in the lower jaw. Troodontids have sickle-claws and raptorial hands, and some of the highest non-avian encephalization quotients, suggesting that they were behaviourally advanced and had keen senses. They had unusually long legs compared to other theropods, with a large, curved claw on their retractable second toes, similar to the "sickle-claw" of the dromaeosaurids.