The smallest known non-avian theropod dinosaur


Non-avian dinosaurs are mostly medium to large-sized animals, and to date all known mature specimens are larger than the most primitive bird, Archaeopteryx1. Here we report on a new dromaeosaurid dinosaur, Microraptor zhaoianus gen. et sp. nov., from the Early Cretaceous Jiufotang Formation of Liaoning, China2. This is the first mature non-avian dinosaur to be found that is smaller than Archaeopteryx1, and it eliminates the size disparity between the earliest birds and their closest non-avian theropod relatives. The more bird-like teeth, the Rahonavis -like ischium and the small number of caudal vertebrae of Microraptor are unique among dromaeosaurids and improve our understanding of the morphological transition to birds. The nearly completely articulated foot shows features, such as distally positioned digit I, slender and recurved pedal claws, and elongated penultimate phalanges, that are comparable to those of arboreal birds3,4,5,6. The discovery of these in non-avian theropods provides new insights for studying the palaeoecology of some bird-like theropod dinosaurs.

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Figure 1: Main slab (V 12330, holotype) containing M. zhaoianus.
Figure 2: Outline of skeleton and identification of the skull with lower jaws and an anterior and posterior dentary tooth of M. zhaoianus (V 12330).
Figure 3: Identification of pelvic girdle, right forelimb and pes of M. zhaoianus (V 12330).
Figure 4: Integument of M. zhaoianus (V 12330).
Figure 5: Phylogenetic relationships of M. zhaoianus.


  1. 1

    Sereno, P. C. The evolution of dinosaurs. Science 284, 2137–2147 (1999).

    CAS  Article  Google Scholar 

  2. 2

    Jin, F. New advances in the late Mesozoic stratigraphic research of western Liaoning, China. Vertebrata PalAsiatica 34, 102– 122 (1996).

    Google Scholar 

  3. 3

    Yaden, D. W. in The Beginnings of Birds (eds Hecht, M. K., Ostrom, J. H., Viohl, G. & Wellnhofer, P.) 91–97 (Freunde des Jura-Museums Eichstatt, Eichstatt, 1985).

    Google Scholar 

  4. 4

    Yalden, D. W. Climbing Archaeopteryx. Archaeopteryx 15, 107–108 (1997).

    Google Scholar 

  5. 5

    Ostrom, J. H. The cursorial origin of avian flight. Mem. Calif. Acad. Sci. 8, 73–81 (1986).

    Google Scholar 

  6. 6

    Feduccia, A. Evidence from claw geometry indicating arboreal habits of Archaeopteryx . Science 259, 790– 793 (1993).

    ADS  CAS  Article  Google Scholar 

  7. 7

    Xu, X. & Wang, X.-L. New psittacosaur (Ornithischia, Ceratopsia) occurrence from the Yixian Formation of Liaoning, China and its stratigraphical significance. Vertebrata PalAsiatica 36, 147–158 (1998).

    Google Scholar 

  8. 8

    Wellnhofer, P. Ein neues Exemplar von Archaeopteryx. Archaeopteryx 6, 1–30 (1988).

    Google Scholar 

  9. 9

    Xu, X., Wang, X.-L. & Wu, X.-C. A dromaeosaurid dinosaur with a filamentous integument from the Yixian Formation of China. Nature 401, 262–266 (1999).

    ADS  CAS  Article  Google Scholar 

  10. 10

    Russell, D. A. & Dong, Z.-M. A nearly complete skeleton of a new troodontid dinosaur from the Early Cretaceous of the Ordos Basin, Inner Mongolia, People's Republic of China. Can. J. Earth Sci. 30, 2163–2173 ( 1994).

    Article  Google Scholar 

  11. 11

    Currie, P. J. Bird-like characteristics of the jaws and teeth of troodontid theropods (Dinosauria, Saurischia). J. Vert. Paleont. 7, 72– 81 (1987).

    Article  Google Scholar 

  12. 12

    Clark, J. M., Perle, M. & Norell, M. A. The skull of Erlicosaurus andrewsi, a Late Cretaceous “Segnosaur” (Theropoda: Therizinosauridae from Mongolia). Am. Mus. Novit. 3115, 1–39 (1994).

    Google Scholar 

  13. 13

    Ostrom, J. H. Osteology of Deinonychus antirrhopus, an unusual theropod dinosaur from the Lower Cretaceous of Montana. Peabody Mus. Nat. Hist. Bull. 30, 1–165 ( 1969).

    Google Scholar 

  14. 14

    Wellnhofer, P. Das siebte Exemplar von Archaeopteryx aus den Solnhofener Schichten. Archaeopteryx 11, 1–47 (1993).

    Google Scholar 

  15. 15

    Currie, P. J. New information on the anatomy and relationships of Dromaeosaurus albertensis (Dinosauria: Theropoda). J. Vert. Paleont. 15, 576–591 (1995).

    Article  Google Scholar 

  16. 16

    Martin, L. D. in Origins of the Higher Groups of Tetrapods (eds Schultze, H.-P. & Trueb, L.) 485–540 (Comstock, Ithaca and London, 1991).

    Google Scholar 

  17. 17

    Zhou, Z. & Martin, L. D. Feathered dinosaur or bird?—a new look at the hand of Archaeopteryx. Smithson. Contrib. Paleobiol. 89, 289–293 ( 1999).

    Google Scholar 

  18. 18

    Forster, C. A., Sampson, S. D., Chiappe, L. M. & Krause, D. W. The theropod ancestry of birds: new evidence from the Late Cretaceous of Madagascar. Science 279, 1915–1919 (1998).

    ADS  CAS  Article  Google Scholar 

  19. 19

    Makovicky, P. & Sues, H.-D. Anatomy and phylogenetic relationships of the theropod dinosaur Microvenator celer from the Lower Cretaceous of Montana. Am. Mus. Novit. 3240, 1– 27 (1998).

    Google Scholar 

  20. 20

    Holtz, T. R. Jr . The phylogenetic position of the Tyrannosauridae: implications for theropod systematics. J. Paleont. 68, 1100– 1117 (1994).

    Article  Google Scholar 

  21. 21

    Norell, M. A. & Makovicky, P. J. Important features of the dromaeosaur skeleton: information from a new specimen. Am. Mus. Novit. 3215, 1–28 (1997).

    Google Scholar 

  22. 22

    Currie, P. J. & Peng, J.-H. A juvenile specimen of Saurornithoides mongoliensis from the Upper Cretaceous of northern China. Can. J. Earth Sci. 30, 2224–2230 (1994).

    Article  Google Scholar 

  23. 23

    Currie, P. J., Rigby, J. K. & Sloan, R. E. in Dinosaur Systematics: Perspectives and Approaches (eds Carpenter, K. & Currie, P. J.) 108– 125 (Cambridge Univ. Press, Cambridge, 1990).

    Google Scholar 

  24. 24

    Wellnhofer, P. A. A new specimen of Archaeopteryx from the Solnhofen Limestone. Nat. Hist. Mus. Los. Angeles County Sci. Ser. 36, 3 –23 (1992).

    Google Scholar 

  25. 25

    Zhou, Z.-H. & Hou, L.-H. Confuciusornis and the early evolution of birds. Vertebrata PalAsiatica 36(2), 136–146 (1998).

    Google Scholar 

  26. 26

    Buffetaut, E., Suteethorn, V. & Tong, H.-Y. The earliest know tyrannosaur from the Lower Cretaceous of Thailand. Nature 381, 689– 691 (1996).

    ADS  CAS  Article  Google Scholar 

  27. 27

    Xu, X., Tang, Z.-L. & Wang, X.-L. A therizinosaurid dinosaur with integumentary structures from China. Nature 399, 350– 354 (1999).

    ADS  CAS  Article  Google Scholar 

  28. 28

    Clark, J. M., Hopson, J. A., Hernandez, R., Fastovsky, D. E. & Montellano, M. Foot posture in a primitive pterosaur. Nature 391, 886–889 (1998).

    ADS  CAS  Article  Google Scholar 

  29. 29

    Chiappe, L. M. Climbing Archaeopteryx? A response to Yalden. Archaeopteryx 15, 109–112 ( 1997).

    Google Scholar 

  30. 30

    Chatterjee, S. The Rise of Birds (John Hopkins Univ. Press, Baltimore, 1997).

    Google Scholar 

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We thank D. Unwin, L. Chiappe, X.-C. Wu, J. Clark and L. Witmer for comments; M.-M. Chang and Y.-Q. Wang for assistance during the course of the work; H.-J. Wang for preparing the specimen; R.-S. Li for making the drawings; and J. Zhang and H.-L. You for taking the photographs. This work was supported by the Special Funds for Major State Basic Research Projects of China, and research grants from the National Geographic Society of the United States, Chinese Natural Science Foundation, and the Chinese Academy of Sciences.

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Correspondence to Xing Xu.

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Xu, X., Zhou, Z. & Wang, X. The smallest known non-avian theropod dinosaur. Nature 408, 705–708 (2000).

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