This timeline of troodontid research is a chronological listing of events in the history of paleontology focused on the troodontids, a group of bird-like theropod dinosaurs including animals like Troodon. Troodontid remains were among the first dinosaur fossils to be reported from North America after paleontologists began performing research on the continent, specifically the genus Troodon itself. Since the type specimen of this genus was only a tooth and Troodon teeth are unusually similar to those of the unrelated thick-headed pachycephalosaurs, Troodon and its relatives would be embroiled in taxonomic confusion for over a century. Troodon was finally recognized as distinct from the pachycephalosaurs by Phil Currie in 1987. By that time many other species now recognized as troodontid had been discovered but had been classified in the family Saurornithoididae. Since these families were the same but the Troodontidae named first, it carries scientific legitimacy. Many milestones of troodontid research occurred between the description of Troodon and the resolution of their confusion with pachycephalosaurs. The family itself was named by Charles Whitney Gilmore in 1924. That same year Henry Fairfield Osborn named the genus Saurornithoides. In the 1960s and 1970s researchers like Russell and Hopson observed that troodontids had very large brains for their body size. Both attributed this enlargement of the brain to a need for processing the animal's especially sharp senses. Also in the 1970s, Barsbold described the new species Saurornithoides (now Zanabazar) junior and named the family Saurornithoidae, but as noted this was just a junior synonym of the Troodontidae in the first place. In the 1980s Gauthier classed them with the dromaeosaurids in the Deinonychosauria. That same decade Jack Horner reported the discovery of Troodon nests in Montana. Interest in the life history of Troodon continued in the 1990s with a study of its growth rates based on histological sections of fossils taken from a bonebed in Montana and the apparent pairing of eggs in Troodon nests. This decade also saw the first potential report of European troodontid remains, although this claim has been controversial. A single mysterious tooth from the Late Jurassic Morrison Formation of the United States was described as the oldest known troodontid remains, although this has also been controversial. In the 2000s, several new kinds of troodontid were named, like Byronosaurus and Sinovenator.
19th century
1850s
1856 Joseph Leidy described the new genus and species Troodon formosus based on an isolated tooth crown. It was one of the first dinosaurs from North America to be formally named, though it was believed to be a lizard until 1877.
1870s
1876 Edward Drinker Cope described the new species Laelaps explanatus. He also described the new genus and species Paronychodon lacustris. Cope described the new species Laelaps cristatus and L. laevifrons. He also described the new genus and species Zapsalis abradens.
1877 Cope became the first to identify Troodon as a theropod dinosaur rather than a lizard.
20th century
1900s
1901 Franz Nopcsa von Felső-Szilvás classified Troodon as a megalosaurid.
1910s
1913 Roy Chapman Andrews described the new genus and species Elopteryx nopcsai. Initially thought to be a bone fragment from a bird, it was later considered a troodontid, but may in fact be an alvarezsaurid.
1920s
1924 Henry Fairfield Osborn described the first troodontid known from more than teeth; a reasonably complete skeleton and skull was placed in the new genus and species Saurornithoides mongoliensis. Charles Whitney Gilmore named the Troodontidae. At the time the name mainly applied to taxa now considered to be pachycephalosaurs because the groups have vaguely similar teeth.
1930s
1932 Gilmore described the new genus and species Polyodontosaurus grandis. C.M. Sternberg described the new genus and species Stenonychosaurus inequalis.
1940s
1945 C.M. Sternberg proves that troodontids are theropods.
1960s
1964 Estes synonymized Paronychodon with the mammal Tripriodon caperatus, based on similar teeth, though this was later shown to be an error.
1969 Russell noted the large brain to body size ratio in troodontids and hypothesized that this relatively high level of brain power was used to process its sharpened senses.
1970s
1974 Rinchen Barsbold described the new species Saurornithoides junior and named the Saurornithoididae.
1975 Colin James Oliver Harrison and Cyril Alexander Walker described the new genus and species Bradycneme draculae. They also described the new genus and species Heptasteornis andrewsi. Both fragmentary fossils were at first identified as birds, and later as troodontids, though researchers currently classify them as alvarezsaurids.
1977 James Hopson noted the large brain to body size ratio in troodontids and hypothesized that this relatively high level of brain power was used to process its sharpened senses.
1980s
1982 Russell and Ronald Séguin interpreted troodontids as carnivores who ate small prey items like mammals, dinosaur eggs and hatchlings, as well as insects. Halszka Osmólska disputed the idea that troodontids used the large claw on their second toe in hunting large prey because it was smaller than the equivalent claw in dromaeosaurids. Horner reported troodontid nests from Montana. Kenneth Carpenter described the new genus and species Pectinodon bakkeri.
1985 Lev Nesov described the new genus and species Pectinodon asiamericanus. Phil Currie hypothesized that troodontids' basisphenoid bullae may have helped them hear very low frequency sounds.
1986
Jacques Gauthier classified troodontids as deinonychosaurs.
1987 James H. Madsen described the new genus and species Borogovia gracilicrus. Currie noted traits in the teeth of Troodon that distinguished them from those of pachycephalosaurs. He split the Troodontidae off from the latter group and noted that the family Saurornithoididae, which then classified many dinosaurs now considered troodontids, was actually it junior synonym. Rinchen Barsbold and others described a new genus the early Cenomanian Khamareen Us site in Mongolia, however he decided not to name it because the specimen was so incomplete.
1990s
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