Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Nest and egg clutches of the dinosaur Troodon formosus and the evolution of avian reproductive traits


Living archosaurs (crocodilians and birds) share several reproductive features, including hard-shelled eggs1, parental care2,3, assembly-line oviducts4 and luteal morphology5. Nevertheless, crocodilians produce many small eggs that they ovulate, shell and deposit en masse, and incubate within sediments or vegetation mounds2,4,6, whereas birds produce fewer but larger eggs7, usually from a single ovary and oviduct3. Further, birds ovulate, shell and lay one egg at a time and incubate eggs directly with body heat3. New discoveries from the Upper Cretaceous of Montana allow re-evaluation of the transition from basal archosaurian to avian reproductive behaviour in the Coelurosauria8,9, the thero-pod dinosaur clade that includes birds. Egg clutches and nests (Figs 1–3) suggest that the small coelurosaurian Troodon formosus (weight, about 50kg) produced two eggs simultaneously at daily or longer intervals and incubated eggs using a combination of soil and direct body contact. Non-avian coelurosaurians thus possess several primitive features found in crocodilians (two functional ovaries and oviducts, lack of egg rotation and chalazae, partial burial of eggs, precocial young) and several derived features shared with birds (relatively larger and potentially asymmetric eggs, one egg produced per oviduct at a time, loss of egg retention, open nests, brooding) (Fig. 4).

This is a preview of subscription content

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.


  1. 1

    Packard, G. C., Tracy, C. R. & Roth, J. J. Biol. Rev. 52, 71–105 (1977).

    CAS  Article  Google Scholar 

  2. 2

    Magnusson, W. E., Vliet, A. C., Pooley, A. C. & Magnusson, R. in Crocodiles and Alligators (eds Ross, C. A. & Garnett, S.) 118–135 (Facts on Files, New York, 1989).

    Google Scholar 

  3. 3

    Gill F. B. Ornithology (Freeman, New York, 1989).

    Google Scholar 

  4. 4

    Palmer, B. D. & Guillette, L. J. Jr Biol. Reprod. 46, 39–47 (1992).

    CAS  Article  Google Scholar 

  5. 5

    Guillette, L. J. Jr et al. J. Morph. 224, 97–110 (1995).

    Article  Google Scholar 

  6. 6

    Coombs, W. P. Jr Spec. Pap. Geol. Soc. Am. 238, 21–53 (1989).

    Google Scholar 

  7. 7

    Blueweiss, L. et al. Oecologia 37, 257–272 (1978).

    ADS  CAS  Article  Google Scholar 

  8. 8

    Clark, J. M., Altangerel, P. & Norell, M. A. Am. Mus. Novit. 3115, 1–39 (1994).

    Google Scholar 

  9. 9

    Holtz, T. R. Jr J. Paleont. 70, 536–538 (1996).

    Article  Google Scholar 

  10. 10

    Horner, J. R. Nature 297, 675–676 (1982).

    ADS  Article  Google Scholar 

  11. 11

    Horner, J. R. in Dinosaurs Past and Present II (eds Czerkas, S. J. & Olson, E. C.) 51–63 (University of Washington Press, Seattle, 1987).

    Google Scholar 

  12. 12

    Hirsch, K. F. & Quinn, B. J. Vert. Paleont. 10, 491–511 (1990).

    CAS  Article  Google Scholar 

  13. 13

    Horner, J. R. & Weishampel, D. B. Nature 332, 256–257 (1988).

    ADS  Article  Google Scholar 

  14. 14

    Horner, J. R. & Weishampel, D. B. Nature 383, 103 (1996).

    ADS  CAS  Article  Google Scholar 

  15. 15

    Dong, Z.-M. & Currie, P. J. Can. J. Earth Sci. 33, 631–636 (1996).

    ADS  Article  Google Scholar 

  16. 16

    Currie, P. J. Natl Geogr. Mag. 189, 96–111 (1996).

    Google Scholar 

  17. 17

    Smith, H. M., Sinelnik, G., Fawcett, J. D. & Jones, R. E. Trans. Kans. Acad. Sci. 75, 107–120 (1973).

    Article  Google Scholar 

  18. 18

    Kinsky, F. C. J. Ornithol. 112, 334–357 (1971).

    Article  Google Scholar 

  19. 19

    Jones, R. E., Smith, H. M. & Bock, C. E. J. Theor. Biol. 161, 527–536 (1993).

    CAS  Article  Google Scholar 

  20. 20

    Sillen-Tullberg, B. & Temrin, H. in Phylogenetics and Ecology (eds Eggleton, P. & Vane-Wright, R. I.) 311–322 (Proc. R. Soc., London, 1994).

    Google Scholar 

  21. 21

    Norell, M. A., Clark, J. M., Chiappe, L. M. & Dashzeveg, D. Nature 378, 774–776 (1995).

    ADS  CAS  Article  Google Scholar 

  22. 22

    Iverson, J. B. & Ewert, M. A. in Egg Incubation (eds Deeming, D. C. & Ferguson, M. W. J.) 87–100 (Cambridge University Press, Cambridge, 1991).

    Book  Google Scholar 

  23. 23

    Hirsch, K. F. in The Paleobiology of Trace Fossils (ed. Donovan, S. K.) 269–294 (Johns Hopkins, Baltimore, 1994).

    Google Scholar 

  24. 24

    Varricchio, D. J. J. Vert. Paleont. 13, 99–104 (1993).

    Article  Google Scholar 

  25. 25

    Stark, J. M. J. Morphol. 222, 113–131 (1994).

    Article  Google Scholar 

  26. 26

    Geist, N. R. & Jones, T. D. Science 272, 712–714 (1996).

    ADS  CAS  Article  Google Scholar 

  27. 27

    Sibley, C. G. & Ahlquist, J. E. Phylogeny and Classification of Brids (Yale University Press, New Haven, 1990).

    Google Scholar 

  28. 28

    Deeming, D. C. in Egg Incubation (eds Deeming, D. C. & Ferguson, M. W. J.) 307–323 (Cambridge University Press, Cambridge, 1991).

    Google Scholar 

  29. 29

    Terres, J. K. The Audubon Society Encyclopedia of North American Birds (Wings Books, New York, 1995).

    Google Scholar 

Download references

Author information



Rights and permissions

Reprints and Permissions

About this article

Cite this article

Varricchio, D., Jackson, F., Borkowski, J. et al. Nest and egg clutches of the dinosaur Troodon formosus and the evolution of avian reproductive traits. Nature 385, 247–250 (1997).

Download citation

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing