Skeletal reconstruction of Saurornithoides junior, copyright Jaime A. Headden.

Belongs within: Maniraptora.

The Troodontidae are a group of small, cursorial theropods known from the Cretaceous of Asia and North America with a single possible representative, Koparion douglassi, also known from the Upper Jurassic (Makovicky & Norell 2004). Certain fragmentary taxa from the late Cretaceous of Europe, such as Bradycneme draculae and Elopteryx nopcsai, have also been suggested to be troodontids but are not universally accepted as such.

Characters (from Makovicky & Norell 2004, possibly excluding Jinfengopteryx): Dentary bearing groove on at least part of labial face containing exits for neurovascular foramina; quadrate with pneumatic foramen present caudally; basicranium with basisphenoid recess absent; internarial bar dorsoventrally flattened; large number of teeth present; mesial dentary teeth closely packed; laterosphenoid with depression present on ventral surface of postorbital process; reduced basal tubera usually lying directly ventral to occipital condyle; transverse processes elongate; distal caudals with sulcus on dorsal midline in place of neural spine; metatarsus asymmetrical with slender metatarsal II markedly shorter than metatarsals III and IV, metatarsal IV robust.

<==Troodontidae [Bradycnemidae, Saurornithoididae]
    |--Jinfengopteryx elegansGC13, P10
    `--+--Mei Xu & Norell 2004GC13, XN04
       |    `--*M. long Xu & Norell 2004XN04
       `--+--Sinovenator Xu, Norell et al. 2002MN04
          |    `--*S. changii Xu, Norell et al. 2002XN02
          `--+--Sinusonasus Xu & Wang 2004GC13, XW04
             |    `--*S. magnodens Xu & Wang 2004XW04
             `--+--Byronosaurus Norell, Makovicky & Clark 2000GC13, MN04
                |    `--B. jaffei Norell, Makovicky & Clark 2000MN04
                `--+--Sinornithoides Russell & Dong 1993GC13, MN04
                   |    `--S. youngi Russell & Dong 1993MN04
                   `--+--Zanabazar junior (Barsbold 1974)GC13, XY11, MN04 [=Saurornithoides juniorP10]
                      |--Troodon Leidy 1856 (see below for synonymy)MN04
                      |    |--*T. formosus Leidy 1856N85 (see below for synonymy)
                      |    |--‘Pectinodon’ asiamericanus Nessov 1995 (n. d.)MN04
                      |    `--T. isfarensis Nessov 1995 (n. d.)MN04
                      `--Saurornithoides Osborn 1924MN04
                           |--S. asiamericanusD07
                           |--S. inaequalisP10
                           |--S. isfarensisD07
                           `--S. mongoliensis Osborn 1924MN04 [=Troodon mongoliensisP88]
Troodontidae incertae sedis:
  Borogovia Osmólska 1987MN04
    `--B. gracilicrus Osmólska 1987MN04
  Bradycneme draculae Harrison & Walker 1975 (n. d.)MN04
  Heptasteornis Harrison & Walker 1975 (n. d.)MN04
    `--H. andrewsi Harrison & Walker 1975 [=Troodon andrewsi]P88
  Koparion Chure 1994H98
    `--K. douglassi Chure 1994MN04
  Tochisaurus Kurzanov & Osmólska 1991MN04
    `--T. nemegtensis Kurzanov & Osmólska 1991MN04
  Elopteryx nopcsai Andrews 1913 (n. d.)MN04
  ‘Laelaps’ cristatus Cope 1876 (n. d.)MN04 [=Dromaeosaurus cristatusO69]
  ‘Laelaps’ explanatus Cope 1876 (n. d.)MN04 [=Dromaeosaurus explanatusO69]
  ‘Laelaps’ laevifrons Cope 1876 (n. d.)MN04 [=Dromaeosaurus laevifronsO69]
  Paronychodon lacustris Cope 1876 (n. d.)MN04
  Zapsalis abradens Cope 1876 (n. d.)MN04

Troodon Leidy 1856 [incl. Pectinodon Carpenter 1982, Polyodontosaurus Gilmore 1932, Stenonychosaurus Sternberg 1932]MN04

*Troodon formosus Leidy 1856N85 [incl. Pectinodon bakkeri Carpenter 1982MN04, Polyodontosaurus grandis Gilmore 1932MN04, Stenonychosaurus inequalis Sternberg 1932MN04, Troodon inequalisLC09]

*Type species of generic name indicated


[D07] Dixon, D. 2007. The Complete Illustrated Encyclopedia of Dinosaurs & Prehistoric Creatures. Hermes House: London.

[GC13] Godefroit, P., A. Cau, Hu D.-Y., F. Escuillié, Wu W. & G. Dyke. 2013. A Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds. Nature 498: 359–362.

[H98] Holtz, T. R., Jr. 1998. A new phylogeny of the carnivorous dinosaurs. Gaia 15: 5–61.

[LC09] Longrich, N. R., & P. J. Currie. 2009. A microraptorine (Dinosauria—Dromaeosauridae) from the Late Cretaceous of North America. Proceedings of the National Academy of Sciences of the USA 106 (3): 5002–5007.

[MN04] Makovicky, P. J., & M. A. Norell. 2004. Troodontidae. In: Weishampel, D. B., P. Dodson & H. Osmólska (eds) The Dinosauria 2nd ed. pp. 184–195. University of California Press: Berkeley.

[N85] Norman, D. 1985. The Illustrated Encyclopedia of Dinosaurs. Salamander Books: London.

[O69] Ostrom, J. H. 1969. Osteology of Deinonychus antirrhopus, an unusual theropod from the Lower Cretaceous of Montana. Bulletin of the Peabody Museum of Natural History 30: 1–165.

[P88] Paul, G. S. 1988. Predatory Dinosaurs of the World: A Complete Illustrated Guide. Simon & Schuster: New York.

[P10] Paul, G. S. 2010. Dinosaurs: A Field Guide. A & C Black.

[XN04] Xu, X., & M. A. Norell. 2004. A new troodontid dinosaur from China with avian-like sleeping posture. Nature 431: 838–841.

[XN02] Xu, X., M. A. Norell, X.-L. Wang, P. J. Makovicky & X.-C. Wu. 2002. A basal troodontid from the Early Cretaceous of China. Nature 415: 780–784.

[XW04] Xu X. & Wang X. 2004. A new troodontid (Theropoda: Troodontidae) from the Lower Cretaceous Yixian Formation of western Liaoning, China. Acta Geologica Sinica (English Edition) 78: 22–26.

[XY11] Xu, X., H. You, K. Du & F. Han. 2011. An Archaeopteryx-like theropod from China and the origin of Avialae. Nature 475: 465–470.

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