Troodon (/ˈtroʊ.ədɒn/ TROH-ə-don; Troödon in older sources) is a former wastebasket taxon and a potentially dubious genus of relatively small, bird-like theropod dinosaurs definitively known from the Campanian age of the Late Cretaceous period (about 77 million years ago).

The genus name is Ancient Greek for "wounding tooth", referring to the teeth, which were different from those of most other theropods known at the time of their discovery.

[2] The type specimen of Troodon has caused problems with classification, as the entire genus is based only on one single tooth from the Judith River Formation.

Troodon has historically been a highly unstable classification and has been the subject of numerous conflicting synonymies with similar theropod specimens.

In 1945, Charles Mortram Sternberg rejected the possibility that Troodon was a pachycephalosaur thanks to its stronger similarity to the teeth of other carnivorous dinosaurs.

In a recent revision of the material by van der Reest & Currie, Polyodontosaurus was determined to be a nomen dubium, not fit for synonymy with other taxa.

[3] In 2017, Evans and colleagues further discussed the undiagnostic nature of the holotype of Troodon formosus and suggested that Stenonychosaurus be used for troodontid skeletal material from the Dinosaur Park Formation.

[10] Later in the same year, Aaron J. van der Reest and Currie came to a similar conclusion as Evans and colleagues and also split much of the material assigned to Stenonychosaurus into a new genus: Latenivenatrix.

[13] They suggested that the description of more complete skeletal material (i.e. containing dental, frontal, and postcranial elements) that can be tied to the holotype could allow the direct testing of the synonymy hypothesis, but re-affirmed that, for now, given the lack of supporting evidence, the synonymy of Troodon and Stenonychosaurus cannot be maintained and that merely remaining untested for 30 years is insufficient justification to accept a proposed lumping of taxa lacking overlapping diagnostic materials.

It proposes that the wear patterns of all Troodon teeth suggest a diet of soft foods - inconsistent with bone chewing, invertebrate exoskeletons, or tough plant items.

It was noted by the authors as having relatively short and robust forelimbs, along with an enlarged second pedal ungual akin to that of the dromaeosaurids compared to more basal troodontids.

It was proposed that derived troodontids had convergently evolved dromaeosaurid-style large second pedal unguals, likely as an adaptation relating to predation.

The authors noted that it is plausible that this may be applicable to other derived troodontids, including Troodon, although this is currently uncertain due to a paucity of sufficient remains of the latter genus.

[3] Remains referred to Troodon are known from the Prince Creek Formation, a rock layer in Alaska that dates from the latest Campanian to Maastrichtian ages of the Late Cretaceous.

The temperature ranged from possibly 2-12°C, which roughly correlates to 36-54°F, and based on Alaska's position in the late Cretaceous, the area faced 120 or so days of winter darkness.

[22] This maniraptoran lived alongside many other reptiles, like the centrosaurine Pachyrhinosaurus perotorum, a species of the saurolophine hadrosaurid Edmontosaurus, the pachycephalosaurin Alaskacephale gangloffi, an unnamed azhdarchid pterosaur, and the tyrannosaurine Nanuqsaurus hoglundi.