Table S1 Select measurements (in mm) of Talos sampsoni (UMNH VP 14979). Abbreviations: CL, centrum length; CW, centrum (transverse) width; DH, distal (craniocaudal or extensor/flexor) height (*also proximodistal height of astragalar body); DW, distal (transverse) width; H, craniocaudal height; L, length; MH, midshaft (craniocaudal or extensor/flexor) height; MW, Mid-shaft (transverse) width; NS, neural spine height; PH, proximal (craniocaudal or extensor/flexor) height; PW, proximal (transverse) width. Asterisk denotes incomplete element with estimate in parentheses. (DOC) Dataset S1 Phylogenetic character list, data matrix, and references for Talos sampsoni (UMNH VP 14979). (DOC) Acknowledgments We thank J. Weinstein for photographs, C. McGarrity, and M. Loewen for assistance with figure preparation, N. Wilkinson for stipple drawings, J. References 1. Therrein F, Henderson DM (2007) My theropod is bigger than yours… or not: estimating body size from skull length in theropods. J Vertebr Paleontol 27: 108–115. 2. Turner AH, Pol D, Clarke JA, Erickson GM, Norell MA (2007) A basal dromaeosaurid and size evolution preceding avian flight. Science 317: 1378–1381. doi:10.1126/science.1144066. 3. Hu D, Hou L, Zhang L, Xu X (2009) A pre-Archaeopteryx troodontid theropod from China with long feathers on the metatarsus. Nature 461: 640–643. 4. Currie PJ (2005) Theropods including birds. In: Currie PJ, Koppelhus EB, eds. Dinosaur Provincial Park: a spectacular ecosystem revealed. Bloomington: Indiana University Press. pp 367–397. 5. Xu X, Norell MA, Wang X, Makovicky PJ, Wu X (2002) A basal troodontid from the Early Cretaceous of China. Nature 415: 780–784. 6. Senter P (2007) A new look at the phylogeny of Coelurosauria (Dinosauria: Theropoda). J Syst Palaeontol 5: 429–463. 7. Xu X, Zhao Q, Norell M, Sullivan C, Hone D, et al. (2009) A new feathered maniraptoran dinosaur fossil that fills a morphological gap in avian origin. Chi Sci Bull 54: 430–435. 8. Varricchio DJ, Jackson FD, Borkowski JJ, Horner JR (1997) Nest and egg clutches of the dinosaur Troodon formosus and the evolution of avian reproductive traits. Nature 385: 247–250. 9. Varricchio DJ, Horner JR, Jackson FD (2002) Embryos and eggs for the Cretaceous theropod dinosaur Troodon formosus. J Vertebr Paleontol 22: 564–576. 10. Varricchio DJ, Jackson FD (2004) Two eggs sunny-side up: Reproductive physiology in the dinosaur Troodon formosus. In: Currie PJ, Koppelhus EB, Shugar MA, Wright JA, eds. Feathered Dragons: Studies on the Transition from Dinosaurs to Birds. Bloomington: Indiana University Press. pp 215–233. 11. Erickson GM, Curry Rogers K, Varricchio DJ, Norell MA, Xu X (2007) Growth patterns in brooding dinosaurs reveals the timing of sexual maturity in non-avian dinosaurs and the genesis of the avian condition. Bio Lett 3: 558–561. 12. Currie PJ, Dong Z-H (2001) New information on Cretaceous troodontids (Dinosauria, Theropoda) from the People’s Republic of China. Can J Earth Sci 38: 1753–1766. 13. Xu X, Norell MA (2004) A new troodontid dinosaur from China with avian-like sleeping posture. Nature 431: 838–841. 14. Li Q, Gao K-Q, Vinther J, Shawkey MD, Clarke JA, et al. (2010) Plumage color patterns of an extinct dinosaur. Science 327: 1369–1372. 15. Currie PJ (1987) Bird-like characteristics of the jaws and teeth of troodontid theropods (Dinosauria, Saurischia). J Vertebr Paleontol 7: 72–81. 16. Makovicky PJ, Norell MA (2004) Troodontidae. In: Weishampel DB, Dodson P, Osmo´lska H, eds. The Dinosauria, Second Edition. Berkeley: University of California Press. pp 184–195. 17. Senter P, Kirkland JI, Bird J, Bartlett JA (2010) A New Troodontid Theropod Dinosaur from the Lower Cretaceous of Utah. PLoS ONE 5(12): e14329. doi:10.1371/journal.pone.0014329. 18. Carpenter K (1982) Baby dinosaurs from the Late Cretaceous Lance and Hell Creek formations, and a description of a new species of theropods. Univ Wyo Contrib Geol 20: 123–134. 19. Longrich N (2008) Small theropod teeth from the Lance Formation of Wyoming, USA. In: Sankey JT, Baszio S, eds. Vertebrate Microfossil Assemblages: their role in paleoecology and paleobiogeography. Bloomington: Indiana University Press. pp 135–158. 20. Chure DJ (1994) Koparion douglassi, a new dinosaur from the Morrison Formation (Upper Jurassic) of Dinosaur National Monument; the oldest troodontid (Theropoda: Maniraptora). BYU Geol Stud 40: 11–15. New Troodontid Theropod from North America Sidote for assistance with post-scan processing of microCT data, M. Getty, E. Lund, J. Golden, and A. Shinya for specimen preparation, and W. Simpson, J. Krishna, C. McGarrity, P. Makovicky, R. Irmis, S. Neidzweizki, Utah Museum of Natural History, Field Museum of Natural History, and Ohio University Office of Research and Sponsored Programs for administration and specimen transportation. Special thanks to R. Irmis (UMNH) and the Bureau of Land Management for permitting histological sampling of the holotype specimen. We thank Corwin Sullivan and an anonymous reviewer for helpful critiques of this work. Access to comparative specimens generously provided by J. Horner, K. Shepherd, M. Norell, P. Currie, and J. Gardner. Free online versions of TNT and Mesquite were made available by the Willi Hennig Society and the Free Software Foundation Inc. Author Contributions Conceived and designed the experiments: LEZ PMO ALT. Performed the experiments: LEZ DJV PMO ALT. Analyzed the data: LEZ DJV PMO ALT. Contributed reagents/materials/analysis tools: LEZ DJV PMO ALT MJK. Wrote the paper: LEZ DJV PMO ALT. 21. Hartman S, Lovelace D, Wahl W (2005) Phylogenetic assessment of a maniraptoran from the Morrison Formation. J Vertebr Paleontol 25(Suppl 3): 67A–68A. 22. Sternberg CM (1932) Two new theropod dinosaurs from the Belly River Formation of Alberta. Can Field Nat 46: 99–105. 23. Leidy J (1856) Notices of remains of extinct reptiles and fishes, discovered by Dr. F. V. Hayden in the bad lands of the Judith River, Nebraska Territory. Proc Acad Natl Sci 8: 72–73. 24. Gilmore CW (1932) A new fossil lizard from the Belly River Formation of Alberta. R Soc Can, Trans 26: 117–120. 25. Romer AS (1966) Vertebrate Paleontology. Third Edition. Chicago: University of Chicago Press. 468 p. 26. Russell DA (1969) A new specimen of Stenonychosaurus from the Oldman Formation (Cretaceous) of Alberta. Can J Earth Sci 6: 595–612. 27. Lambe LM (1902) New genera and species from the Belly River Series (mid- Cretaceous). Geological Survey of Canada. Contr Can Paleontol 3: 25–81. 28. Barsbold R (1974) Saurornithoididae, a new family of small theropod dinosaurs from central Asia and North America. Paelaeontol Pol 30: 5–22. 29. Currie PJ, Rigby JK, Sloan RE (1990) Theropod teeth from the Judith River Formation of southern Alberta, Canada. In: Carpenter K, Currie PJ, eds. Dinosaur Systematics: Perspectives and Approaches. Cambridge: Cambridge University Press. pp 107–125. 30. Currie PJ (1992) Saurischian dinosaurs of the Late Cretaceous of Asia and North America. In: Mateer NJ, Chen PJ, eds. Aspects of Nonmarine Cretaceous Geology. Beijing: Ocean Press. pp 237–249. 31. Peng J, Russell AP, Brinkman DB (2001) Vertebrate microsite assemblages (exclusive of mammals) from the Foremost and Oldman Formations of the Judith River Group (Campanian) of southeastern Alberta: an illustrated guide. Prov Mus Alberta, Nat Hist Occas Pap 25: 1–546. 32. Norell MA, Makovicky PJ, Bever GS, Balanoff AM, Clark JM, et al. (2009) A review of the Mongolian Cretaceous dinosaur Saurornithoides. Am Mus Novit 3654: 1–63. 33. Zanno LE, Varricchio DJ, Titus AL, Wilkins N, Knell MJ (2009) A new troodontid (Theropoda: Paraves) specimen from the upper Campanian Kaiparowits Formation, Southern Utah: estimating the taxonomic diversity of North American Troodontidae. J Vertebr Paleontol 29(Suppl 3): 205A. 34. Norell MA, Makovicky PJ, Clark JM (2000) A new troodontid theropod from Ukhaa Tolgod, Mongolia. J Vertebr Paleontol 20: 7–11. 35. Maddison WP, Maddison DR (2008) Mesquite: A modular system for evolutionary analysis. Version 2.5. Available: http://mesquiteproject.org. Accessed 2010 Jan 15. 36. Goloboff P, Farris JS, Nixon K (2008) TNT (Tree analysis using New Technology) (BETA), Tucama´n, Argentina: Published by the authors. 37. Coddington J, Scharff N (1994) Problems with zero-length branches. Cladistics 10: 415–423. 38. Finden CR, Gordon AD (1986) Obtaining common pruned trees. J Classif 2: 255–276. 39. Felsenstein J (1985) Confidence limits on phylogenies: an approach using the bootstrap. Evol 39: 783–791. 40. Goloboff P, Farris JS, Ka¨llersjo¨ M, Oxelman B, Ram´ırez MJ, et al. (2003) Improvements to resampling measures of group support. Cladistics. 19: 324–332. 41. Owen R (1842) Report on British fossil reptiles. Part II. In: Report of the eleventh meeting of the British Association for the Advancement of Science. London: John Murray. pp 60–204. PLoS ONE | www.plosone.org 18 September 2011 | Volume 6 | Issue 9 | e24487