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.

  • Article
  • Published:

A mid-Cretaceous tyrannosauroid and the origin of North American end-Cretaceous dinosaur assemblages


Late Cretaceous dinosaur assemblages of North America—characterized by gigantic tyrannosaurid predators, and large-bodied herbivorous ceratopsids and hadrosaurids—were highly successful from around 80 million years ago (Ma) until the end of the ‘Age of Dinosaurs’ 66 Ma. However, the origin of these iconic faunas remains poorly understood because of a large, global sampling gap in the mid-Cretaceous, associated with an extreme sea-level rise. We describe the most complete skeleton of a predatory dinosaur from this gap, which belongs to a new tyrannosauroid theropod from the Middle Turonian (~92 Ma) of southern Laramidia (western North America). This taxon, Suskityrannus hazelae gen. et sp. nov., is a small-bodied species phylogenetically intermediate between the oldest, smallest tyrannosauroids and the gigantic, last-surviving tyrannosaurids. The species already possesses many key features of the tyrannosaurid bauplan, including the phylogenetically earliest record of an arctometatarsalian foot in tyrannosauroids, indicating that the group developed enhanced cursorial abilities at a small body size. Suskityrannus is part of a transitional Moreno Hill (that is, Zuni) dinosaur assemblage that includes dinosaur groups that became rare or were completely absent in North America around the final 15 Myr of the North American Cretaceous before the end-Cretaceous mass extinction, as well as small-bodied forebears of the large-bodied clades that dominated at this time.

This is a preview of subscription content, access via your institution

Access options

Buy this article

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: S. hazelae gen. et sp. nov. holotype skull (MSM P4754) and reconstruction.
Fig. 2: Skeletal element of both specimens of S. hazelae gen. et sp. nov. and reconstruction.
Fig. 3: Histology section (in plain light) of the right femur (MSM P6178) of S. hazelae gen. et sp. nov. taken near the midshaft.
Fig. 4: Relationships of S. hazelae gen. et sp. nov. among tyrannosauroids and its place within the transitionary Moreno Hill dinosaur assemblage.

Similar content being viewed by others

Data availability

The data that support the findings of this study are provided in the Supplementary Information and Supplementary Data 13. High-quality images of the histology sections are available on Morphobank (project number 3298; permalink: Reconstructed computed tomography slices (in .tiff stack format) are available for the holotype skull (MSM P4754) at Data have been deposited in ZooBank under Life Science Identifier (for the new genus and species).


  1. Russell, L. S. Upper Cretaceous dinosaur faunas of North America. Proc. Am. Phil. Soc. 69, 133–159 (1930).

    Google Scholar 

  2. Weishampel, D. et al. in The Dinosauria (eds Weishampel, D. B., Dodson, P. & Osmólska, H.) 517–606 (Univ. California Press, 2004).

  3. Brusatte, S. L. et al. The extinction of the dinosaurs. Biol. Rev. 90, 628–642 (2015).

    Article  Google Scholar 

  4. Renne, P. R. et al. Time scales of critical events around the Cretaceous–Paleogene boundary. Science 339, 684–687 (2013).

    Article  CAS  Google Scholar 

  5. Benson, R. B. et al. Cretaceous tetrapod fossil record sampling and faunal turnover: implications for biogeography and the rise of modern clades. Palaeogeogr. Palaeoclimatol. Palaeoecol. 372, 88–107 (2013).

    Article  Google Scholar 

  6. Fastovsky, D. E. et al. Shape of Mesozoic dinosaur richness. Geology 32, 877–880 (2004).

    Article  Google Scholar 

  7. Miller, K. G. et al. The Phanerozoic record of global sea-level change. Science 310, 1293–1298 (2005).

    Article  CAS  Google Scholar 

  8. Archibald, J. D. et al. in Lower to Middle Cretaceous Terrestrial Ecosystems Vol. 14 (eds Lucas, S. G., Kirkland, J. I. & Estep, J. W.) 21–28 (1998).

  9. Averianov, A. & Sues, H.-D. Skeletal remains of Tyrannosauroidea (Dinosauria: Theropoda) from the Bissekty Formation (Upper Cretaceous: Turonian) of Uzbekistan. Cretac. Res. 34, 284–297 (2012).

    Article  Google Scholar 

  10. Sues, H.-D. & Averianov, A. Turanoceratops tardabilis—the first ceratopsid dinosaur from Asia. Naturwissenschaften 96, 645–652 (2009).

    Article  CAS  Google Scholar 

  11. Kirkland, J. I. & Wolfe, D. G. First definitive therizinosaurid (Dinosauria; Theropoda) from North America. J. Vert. Paleontol. 21, 410–414 (2001).

    Article  Google Scholar 

  12. Mcdonald, A. T., Wolfe, D. G. & Kirkland, J. I. A new basal hadrosauroid (Dinosauria: Ornithopoda) from the Turonian of New Mexico. J. Vert. Paleontol. 30, 799–812 (2010).

    Article  Google Scholar 

  13. Wolfe, D. G. & Kirkland, J. I. Zuniceratops christopheri n.gen. & n.sp., a ceratopsian dinosaur from the Moreno Hill Formation (Cretaceous, Turonian) of west-central New Mexico. Bull. N. Mexico Mus. Nat. Hist. Sci. 14, 303–317 (1998).

    Google Scholar 

  14. Padian, K. & May, C. L. The earliest dinosaurs. Bull. N. Mexico Mus. Nat. Hist. Sci. 3, 379–381 (1993).

    Google Scholar 

  15. Gauthier, J. A. Saurischian monophyly and the origin of birds. Mem. Calif. Acad. Sci. 8, 1–55 (1986).

    Google Scholar 

  16. Von Huene, F. Das natürliche system der Saurischia. Zentralbl. Min. Geol. Pal. B 1914, 154–158 (1914).

    Google Scholar 

  17. Sereno, P. C. et al. Tyrannosaurid skeletal design first evolved at small body size. Science 326, 418–422 (2009).

    Article  CAS  Google Scholar 

  18. Osborn, H. F. Tyrannosaurus and other Cretaceous carnivorous dinosaurs. Bull. Am. Mus. Nat. Hist. 21, 259–265 (1905).

    Google Scholar 

  19. Holtz Jr, T. R. in The Dinosauria 2nd edn (eds Weishampel, D. B., Dodson, P. & Osmolska, H.) 111–136 (Univ. California Press, 2004).

  20. Molenaar, C. M. et al. Regional stratigraphic cross section of Cretaceous rocks from east-central Arizona to the Oklahoma Panhandle Miscellaneous Field Studies Map MF-2382 (US Geological Survey, 2002).

  21. Hone, D. W., Farke, A. A. & Wedel, M. J. Ontogeny and the fossil record: what, if anything, is an adult dinosaur? Biol. Lett. 12, 20150947 (2016).

    Article  Google Scholar 

  22. Irmis, R. B. Axial skeleton ontogeny in the Parasuchia (Archosauria: Pseudosuchia) and its implications for ontogenetic determination in archosaurs. J. Vert. Paleontol. 27, 350–361 (2007).

    Article  Google Scholar 

  23. Brochu, C. A. Closure of neurocentral sutures during crocodilian ontogeny: implications for maturity assessment in fossil archosaurs. J. Vert. Paleontol. 16, 49–62 (1996).

    Article  Google Scholar 

  24. Fowler, D. W., Woodward, H. N., Freedman, E. A., Larson, P. L. & Horner, J. R. Reanalysis of “Raptorex kriegsteini”: a juvenile tyrannosaurid dinosaur from Mongolia. PLoS ONE 6, e21376 (2011).

    Article  CAS  Google Scholar 

  25. Tsuihiji, T. et al. Cranial osteology of a juvenile specimen of Tarbosaurus bataar (Theropoda, Tyrannosauridae) from the Nemegt Formation (Upper Cretaceous) of Bugin Tsav, Mongolia. J. Vert. Paleontol. 31, 497–517 (2011).

    Article  Google Scholar 

  26. Erickson, G. M. et al. Was dinosaurian physiology inherited by birds? Reconciling slow growth in Archaeopteryx. PLoS ONE 4, e7390 (2009).

    Article  Google Scholar 

  27. Xu, X. et al. A basal tyrannosauroid dinosaur from the Late Jurassic of China. Nature 439, 715–718 (2006).

    Article  CAS  Google Scholar 

  28. Currie, P. J., Hurum, J. H. & Sabath, K. Skull structure and evolution in tyrannosaurid dinosaurs. Acta Palaeontol. Pol. 48, 227–234 (2003).

    Google Scholar 

  29. Xu, X. et al. Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroids. Nature 431, 680–684 (2004).

    Article  CAS  Google Scholar 

  30. Carr, T. D. & Williamson, T. E. Bistahieversor sealeyi, gen. et sp. nov., a new tyrannosauroid from New Mexico and the origin of deep snouts in Tyrannosauroidea. J. Vert. Paleontol. 30, 1–16 (2010).

    Article  Google Scholar 

  31. Brusatte, S. L., Lloyd, G. T., Wang, S. C. & Norell, M. A. Gradual assembly of avian body plan culminated in rapid rates of evolution across the dinosaur–bird transition. Curr. Biol. 24, 2386–2392 (2014).

    Article  CAS  Google Scholar 

  32. Xu, X. et al. A gigantic feathered dinosaur from the Lower Cretaceous of China. Nature 484, 92–95 (2012).

    Article  CAS  Google Scholar 

  33. Brusatte, S. L. et al. Tyrannosaur paleobiology: new research on ancient exemplar organisms. Science 329, 1481–1485 (2010).

    Article  CAS  Google Scholar 

  34. Brusatte, S. L., Carr, T. D. & Norell, M. A. The osteology of Alioramus, a gracile and long-snouted tyrannosaurid (Dinosauria: Theropoda) from the Late Cretaceous of Mongolia. Bull. Am. Mus. Nat. Hist. 366, 1–197 (2012).

    Article  Google Scholar 

  35. Brusatte, S. L., Averianov, A., Sues, H. D., Muir, A. & Butler, I. B. New tyrannosaur from the mid-Cretaceous of Uzbekistan clarifies evolution of giant body sizes and advanced senses in tyrant dinosaurs. Proc. Natl Acad. Sci. USA 113, 2447–2452 (2016).

    Article  Google Scholar 

  36. Rauhut, O. W., Milner, A. C. & Moore-Fay, S. Cranial osteology and phylogenetic position of the theropod dinosaur Proceratosaurus bradleyi (Woodward, 1910) from the Middle Jurassic of England. Zoo. J. Linnean Soc. 158, 155–195 (2010).

    Article  Google Scholar 

  37. Holtz, T. R. Jr The arctometatarsalian pes, an unusual structure of the metatarsus of Cretaceous Theropoda (Dinosauria: Saurischia). J. Vert. Paleontol. 14, 480–519 (1995).

    Article  Google Scholar 

  38. Brusatte, S. L. & Carr, T. D. The phylogeny and evolutionary history of tyrannosauroid dinosaurs. Sci. Rep. 6, 20252 (2016).

    Article  CAS  Google Scholar 

  39. Loewen, M. A., Irmis, R. B., Sertich, J. J., Currie, P. J. & Sampson, S. D. Tyrant dinosaur evolution tracks the rise and fall of Late Cretaceous oceans. PLoS ONE 8, e79420 (2013).

    Article  CAS  Google Scholar 

  40. Hutt, S., Naish, D., Martill, D. M., Barker, M. J. & Newbery, P. A preliminary account of a new tyrannosauroid theropod from the Wessex Formation (Early Cretaceous) of southern England. Cretac. Res. 22, 227–242 (2001).

    Article  Google Scholar 

  41. Li, D., Norell, M. A., Gao, K.-Q., Smith, N. D. & Makovicky, P. J. A longirostrine tyrannosauroid from the Early Cretaceous of China. Proc. R. Soc. Lond. B 277, 183–190 (2009).

    Article  Google Scholar 

  42. Zanno, L. E. & Makovicky, P. J. On the earliest record of Cretaceous tyrannosauroids in western North America: implications for an Early Cretaceous Laurasian interchange event. Historical Biol. 23, 317–325 (2011).

    Article  Google Scholar 

  43. Rylaarsdam, J. R., Varban, B. L., Plint, A. G., Buckley, L. G. & McCrea, R. T. Middle Turonian dinosaur paleoenvironments in the Upper Cretaceous Kaskapau Formation, northeast British Columbia. Can. J. Earth Sci. 43, 631–652 (2006).

    Article  Google Scholar 

  44. Eaton, J. G. et al. Nonmarine extinction across the Cenomanian–Turonian boundary, southwestern Utah, with a comparison to the Cretaceous–Tertiary extinction event. Geol. Soc. Am. Bull. 109, 560–567 (1997).

    Article  Google Scholar 

  45. Fiorillo, A. R. et al. An unusual association of hadrosaur and therizinosaur tracks within Late Cretaceous rocks of Denali National Park, Alaska. Sci. Rep. 8, 11706 (2018).

    Article  Google Scholar 

  46. Smith, J. A., Zanno, L. E. & Lockley, M. Large tetradactyl footprints in the Upper Cretaceous Hunter Canyon formation of western Colorado: ichnological evidence for therizinosaurids in the Campanian of North America? In Society of Vertebrate Paleontology 76th Annual Meeting 227 (Society of Vertebrate Paleontology, 2016).

  47. Goloboff, P. A., Farris, J. S. & Nixon, K. C. TNT, a free program for phylogenetic analysis. Cladistics 24, 774–786 (2008).

    Article  Google Scholar 

  48. Coddington, J. & Scharff, N. Problems with zero-length branches. Cladistics 10, 415–423 (1994).

    Article  Google Scholar 

  49. Paleobiology Database (accessed 24 October 2018);

Download references


We thank M. Norell, T. Carr, N. Longrich, T. Holtz, D. Evans and P. Makovicky for discussion, and L. Zanno and G. McCullough for specimen numbers. We thank C. M. ‘Kay’ Molenaar for input on our stratigraphic interpretations. We thank C. Griffin and S. Werning for help imaging the histology slides, and M. Stocker for computed tomography scanning help. Field work was conducted under BLM permit MSM-8172-RS-1A (to D.G.W.). Preparation of the specimens was conducted by H. Bollan and P. Bollan (Grand Junction, Colorado). We thank B. Anderson for discovery and documentation of the holotype specimen. R. Gaston of Gaston Design provided study casts of the material to R.K.D., D.G.W. and J.I.K. This work was funded by the Discovery Channel (to J.I.K. and D.G.W.) and the Department of Geosciences at Virginia Tech (to S.J.N.). We specifically thank M. Harrington and the Pueblo of Zuni Tribal Council for discussion of the name Suskityrannus. The larger project—the ‘Zuni Basin Paleontology Project’, led by the Wolfe family—was supported by members of the Southwest Palaeontological Society, the Arizona Museum of Natural History and dozens of volunteers since 1996. We thank M. Hayden and S. Carney for UGS technical reviews.

Author information

Authors and Affiliations



S.J.N., R.K.D., M.A.L. and S.L.B. designed the research project. S.J.N. and A.H.T. composed the figures. S.L.B. and M.A.L. conducted the phylogenetic analyses. S.J.N., R.K.D., M.A.L., S.L.B. and N.D.S. interpreted the anatomy. D.G.W., R.K.D. and J.I.K. oversaw the field work and geological analysis. J.I.K. oversaw preparation of the specimens. S.J.N., R.K.D., M.A.L., S.L.B., N.D.S., A.H.T., J.I.K., A.T.M. and D.G.W. wrote the manuscript.

Corresponding author

Correspondence to Sterling J. Nesbitt.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Figures, differential diagnosis, geology, supplementary description of localities, ontogenetic age assessment, measurements, phylogenetic results, Late Cretaceous diversity data, dinosaur assemblage members and supplementary references

Reporting Summary

Supplementary Data 1

TNT data matrix used for the phylogenetic analysis. Loewen tyrannosauroid phylogeny dataset with Suskityrannus

Supplementary Data 2

TNT data matrix used for the phylogenetic analysis. Brusatte and Carr 2016 tyrannosauroid phylogeny dataset with Suskityrannus

Supplementary Data 3

TNT data matrix used for the phylogenetic analysis. Brusatte et al. 2014 theropod dataset with Suskityrannus

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Nesbitt, S.J., Denton, R.K., Loewen, M.A. et al. A mid-Cretaceous tyrannosauroid and the origin of North American end-Cretaceous dinosaur assemblages. Nat Ecol Evol 3, 892–899 (2019).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


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