Timeline of troodontid research


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 ''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">1856 in paleontology">1856

1870s

1876">1876 in paleontology">1876

1877">1877 in paleontology">1877

20th century

1900s

1901">1901 in paleontology">1901

1910s

1913">1913 in paleontology">1913

1920s

1924">1924 in paleontology">1924

1930s

1932">1932 in paleontology">1932

1940s

1945">1945 in paleontology">1945

  • C.M. Sternberg proves that troodontids are theropods.

1960s

1964">1964 in paleontology">1964

1969">1969 in paleontology">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">1974 in paleontology">1974

1975">1975 in paleontology">1975

1977">1977 in paleontology">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">1982 in paleontology">1982

1985">1985 in paleontology">1985

1986">1986 in paleontology">1986

1987">1987 in paleontology">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

1990">1990 in paleontology">1990

  • Osmólska and Barsbold reported possible troodontid remains from Europe, although without substantial evidentiary support. They also published the first evolutionary tree of the Troodontids, based on changes in proportions of the second phalanx in the second toe rather than a standard cladistic character matrix. They found Troodon formosus to be the sister taxon to the genus Saurornithoides and Borogovia.
  • Barsbold and 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.
  • Currie and others proposed that Paronychodon teeth were not the remains of a distinct species but were actually injured, diseased, or deformed teeth belonging to many different species.

1991">1991 in paleontology">1991

1993">1993 in paleontology">1993

  • Russell and Dong Zhiming described the new genus and species Sinornithoides youngi. They found troodontids to be the sister group of a clade containing the oviraptorosaurs and therizinosaurs.
  • Stafford Howse and Andrew Milner reported possible troodontid remains from Europe, although without substantial evidentiary support.
  • David Varricchio studied the remains of many Troodon formosus preserved in a bonebed. The co-occurrence of so many individuals of the same species preserved together suggested to him that this species may have been a social animal. Varrichio also studied histological sections of bones taken from individuals preserved in this bonebed at varying stages of growth. He found that it took less than five years for a hatchling Troodon to reach adult size, at which point it stopped growing.

1994">1994 in paleontology">1994

  • Daniel Chure described the new genus and species Koparion douglassi. This Late Jurassic taxon may be the oldest known troodontid, but since the type specimen consisted only of a single tooth it is impossible to know for sure if it is actually a troodontid.
  • Thomas Richard Holtz Jr found troodontids to be the sister group to the ornithomimosaurs in the Bullatosauria.
  • Holtz and others noted similarities in the teeth of troodontids and iguanine lizards and suggested that the former family may not have been strict carnivores.

1995">1995 in paleontology">1995

1996">1996 in paleontology">1996

  • Darla Zelenitsky and Leonard Hills described the eggs of Troodon formosus. They found that the surface of Troodon eggs were smooth and their pores occurred singly or in pairs. When viewed in thin section, the eggshell exhibited two distinct layers. The inner layer was composed of blocky calcite crystals while crystals composing the outer layer were prismatic. Similar eggs in the past had been attributed to primitive ornithopods and relatives of Protoceratops but were actually laid by theropods.

1997">1997 in paleontology">1997

  • Paul Callistus Sereno classified troodontids as deinonychosaurs.
  • Richard Ciffeli and others reported possible troodontid teeth from a Cenomanian-aged microvertebrate fossil site in Utah. The teeth are similar to those referred to the controversial genus Paronychodon. If these fossils really are troodontid, they might well be the oldest known occurrence of the family in North America.
  • Varricchio and others published a detailed study of troodontid nests from Montana. The eggs were laid in a tight circular formation with the narrow end pointed down. Although the eggs were at least partially covered by sediment the nest itself was basically open. Since one nest preserved a partial adult skeleton, the researchers concluded that these troodontids may have brooded their eggs like modern birds. The researchers also subjected the positions of individual eggs to statistical analysis and found that the eggs seemed to cluster in pairs. This is evidence that these dinosaurs had two functioning oviducts. Varrichio and the other researchers also noted that the ratio between the size of the egg and the body of the mother in these troodontids were between those of modern crocodiles and birds.

1998">1998 in paleontology">1998

  • Peter Makovicky and Hans-Dieter Sues classified troodontids as deinonychosaurs.
  • Holtz and others noted similarities in the teeth of troodontids and iguanine lizards and suggested that the former family may not have been strict carnivores.
  • Holtz found that troodontids were the sister group to the ornithomimosaurs.
  • Catherine Forster and others found that troodontids were the sister group of the avialans.
  • Sereno defined the Troodontidae as all taxa more closely related to Troodon formosus than to Velociraptor mongoliensis.

1999">1999 in paleontology">1999

  • Fernando Emilio Novas and others reported a possible troodontid specimen from Coniacian to Turonian-aged sediments in South America. If this report is accurate it suggests that after first evolving in Asia, troodontids dispersed into North America and then traveled further down to South America.
  • Sereno classified troodontids as deinonychosaurs.

21st century

2000s

2000">2000 in paleontology">2000

  • Mark Norell, Makovicky and Clark described the new genus and species Byronosaurus jaffei. They performed a cladistic analysis of the troodontids based on 38 characters in 10 taxa. Norell and others found troodontids to be the sister group of a clade containing the oviraptorosaurs and therizinosaurs. They found Byronosaurus to be the sister group of a polytomy consisting of the two Saurornithoides species from Asia and Troodon formosus of North America. Sinornithoides was the sister group to this clade, with the unnamed Khamaryn Us troodontid being the sister group to all others.

2001">2001 in paleontology">2001

  • Norell and others studied the evolutionary relationships between troodontids and other coelurosaurs. They found troodontids to be the sister group of a clade containing the oviraptorosaurs and therizinosaurs. Within Troodontidae they obtained similar results to their 2000 study, although this time they excluded the unnamed Khamaryn Us trodontid.
  • Makovicky and Gerald Grellet-Tinner noted commonalities between the type of egg microstructure seen in troodontid eggs and those of modern neognathous birds. However, they also noted that these similarities may have evolved separately rather than being inherited from a shared common ancestor.
  • Kevin Padian, Ji Qiang and Ji Shuan published a review of known feathered dinosaurs and their implications for the origin of flight. The authors observed that many aspects of the distribution of feather homologues in the dinosaur family tree met the expectations of earlier phylogenetic hypotheses, yet feathers were notably absent among troodontids despite the family's derived position within the coelurosaur family tree.

2002">2002 in paleontology">2002

  • Xu Xing and others performed a cladistic analysis of the Dromaeosauridae. They found the Troodontidae to be to sister taxon of the Dromaeosauridae.
  • Xu and others described the new genus and species Sinovenator changii. They performed a cladistic analysis of the troodontidae based on the same character matrix as Norell and others used back in 2001. Xu and the others recovered the same relationships among troodontids as the other researchers with the exception of Sinovenator's presence at the base of the tree. Since it was extremely primitive for a troodontid Sinovenator may offer insights into the family's relationships with other theropod groups.

2004">2004 in paleontology">2004

2005">2005 in paleontology">2005

2007">2007 in paleontology">2007

2009">2009 in paleontology">2009

2010s

2010">2010 in paleontology">2010

2011">2011 in paleontology">2011

2012">2012 in paleontology">2012

2014">2014 in paleontology">2014

2017">2017 in paleontology">2017

2019">2019 in paleontology">2019

2020