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).

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 [Saurornithoididae]
    |--Jinfengopteryx GC13
    `--+--Mei Xu & Norell 2004 GC13, XN04
       |    `--*M. long Xu & Norell 2004 XN04
       `--+--Sinovenator Xu, Norell et al. 2002 MN04
          |    `--*S. changii Xu, Norell et al. 2002 XN02
          `--+--Sinusonasus Xu & Wang 2004 GC13, XW04
             |    `--*S. magnodens Xu & Wang 2004 XW04
             `--+--Byronosaurus Norell, Makovicky & Clark 2000 GC13, MN04
                |    `--B. jaffei Norell, Makovicky & Clark 2000 MN04
                `--+--Sinornithoides Russell & Dong 1993 GC13, MN04
                   |    `--S. youngi Russell & Dong 1993 MN04
                   `--+--Zanabazar GC13
                      |--Troodon Leidy 1856 (see below for synonymy) MN04
                      |    |--*T. formosus Leidy 1856 N85 (see below for synonymy)
                      |    |--‘Pectinodon’ asiamericanus Nessov 1995 (n. d.) MN04
                      |    `--T. isfarensis Nessov 1995 (n. d.) MN04
                      `--Saurornithoides Osborn 1924 MN04
                           |--S. asiamericanus D07
                           |--S. isfarensis D07
                           |--S. junior Barsbold 1974 MOW02
                           `--S. mongoliensis Osborn 1924 MOW02 [=Troodon mongoliensis P88]

Troodontidae incertae sedis:
  Borogovia Osmólska 1987 MN04
    `--B. gracilicrus Osmólska 1987 MN04
  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 1994 H98
    `--K. douglassi Chure 1994 MN04
  Tochisaurus Kurzanov & Osmólska 1991 MN04
    `--T. nemegtensis Kurzanov & Osmólska 1991 MN04
  Elopteryx [Elopterygidae] MN04
    `--E. nopcsai Andrews 1913 (n. d.) MN04
  ‘Laelaps’ cristatus Cope 1876 (n. d.) MN04 [=Dromaeosaurus cristatus O69]
  ‘Laelaps’ explanatus Cope 1876 (n. d.) MN04 [=Dromaeosaurus explanatus O69]
  ‘Laelaps’ laevifrons Cope 1876 (n. d.) MN04 [=Dromaeosaurus laevifrons O69]
  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 1856 N85 [incl. Pectinodon bakkeri Carpenter 1982 MN04, Polyodontosaurus grandis Gilmore 1932 MN04, Stenonychosaurus inequalis Sternberg 1932 MN04]

*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.

[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 (reprinted 2000). 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.

[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.

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