Baby tyrannosaurid bones and teeth from the Late Cretaceous of western North America1

Publication: Canadian Journal of Earth Sciences
25 January 2021


Tyrannosaurids were the apex predators of Late Cretaceous Laurasia and their status as dominant carnivores has garnered considerable interest since their discovery, both in the popular and scientific realms. As a result, they are well studied and much is known of their anatomy, diversity, growth, and evolution. In contrast, little is known of the earliest stages of tyrannosaurid development. Tyrannosaurid eggs and embryos remain elusive, and juvenile specimens — although known — are rare. Perinatal tyrannosaurid bones and teeth from the Campanian–Maastrichtian of western North America provide the first window into this critical period of the life of a tyrannosaurid. An embryonic dentary (cf. Daspletosaurus) from the Two Medicine Formation of Montana, measuring just 3 cm long, already exhibits distinctive tyrannosaurine characters like a “chin” and a deep Meckelian groove, and reveals the earliest stages of tooth development. When considered together with a remarkably large embryonic ungual from the Horseshoe Canyon Formation of Alberta, minimum hatchling size of tyrannosaurids can be roughly estimated. A perinatal premaxillary tooth from the Horseshoe Canyon Formation likely pertains to Albertosaurus sarcophagus and it shows small denticles on the carinae. This tooth shows that the hallmark characters that distinguish tyrannosaurids from other theropods were present early in life and raises questions about the ontogenetic variability of serrations in premaxillary teeth. Sedimentary and taphonomic similarities in the sites that produced the embryonic bones provide clues to the nesting habits of tyrannosaurids and may help to refine the prospecting search image in the continued quest to discover baby tyrannosaurids.


Les tyrannosauridés étaient les prédateurs apicaux de la Laurasie au Crétacé tardif, et leur statut de carnivores dominants a suscité un intérêt considérable depuis leur découverte, tant au sein du grand public que dans les milieux scientifiques. Ils sont par conséquent bien étudiés, et les connaissances sur leur anatomie, leur diversité, leur croissance et leur évolution sont vastes. En revanche, on en sait peu sur les premières étapes de leur développement. Les œufs et embryons de tyrannosauridés manquent toujours à l’appel et, bien que certains soient connus, les spécimens juvéniles sont rares. Des os et dents de tyrannosauridés périnataux du Campanien–Maastrichtien de l’ouest de l’Amérique du Nord constituent la première fenêtre sur cette période clé de la vie d’un tyrannosauridé. Un os dentaire embryonnaire (cf. Daspletosaurus) de la Formation de Two Medicine, au Montana, faisant seulement 3 cm de long, présente déjà des caractères distinctifs des tyrannosaurinés, comme un « menton » et un profond sillon de Meckel, et révèle les toutes premières étapes du développement des dents. Ces observations, combinées à une phalange unguéale embryonnaire remarquablement longue de la Formation de Horseshoe Canyon en Alberta, permettent d’estimer grossièrement la taille minimum de tyrannosauridés nouvellement éclos. Une dent prémaxillaire périnatale de la Formation de Horseshoe Canyon appartient probablement à Albertosaurus sarcophagus et présente de petits denticules sur les carènes. Cette dent démontre que les caractères typiques qui distinguent les tyrannosauridés d’autres théropodes étaient présents tôt durant la vie et soulève des questions concernant la variabilité ontogénétique de dentelures sur les dents prémaxillaires. Des similitudes sédimentaires et taphonomiques dans les sites qui ont produit des ossements d’embryons fournissent des indices sur les habitudes de nidification des tyrannosauridés et pourraient aider à préciser l’image recherchée pour la prospection dans la quête continue de bébés de tyrannosauridé. [Traduit par la Rédaction]

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Araújo R., Castanhinha R., Martins R.M.S., Mateus O., Hendrickx C., Beckmann F., et al. 2013. Filling the gaps of dinosaur eggshell phylogeny: late Jurassic Theropod clutch with embryos from Portugal. Scientific Reports, 3: 1924.
Arbour V.M. and Currie P.J. 2013. Euoplocephalus tutus and the diversity of Ankylosaurid dinosaurs in the late Cretaceous of Alberta, Canada, and Montana, USA. PLoS One, 8: e62421.
Atterholt J., Hutchison J.H., and O’Connor J.K. 2018. The most complete enantiornithine from North America and a phylogenetic analysis of the Avisauridae. PeerJ, 6: e5910.
Balanoff A.M. and Rowe T. 2007. Osteological description of an embryonic skeleton of the extinct Elephant Bird, Aepyornis (Palaeognathae: Ratitae). Journal of Vertebrate Paleontology, 27: 1–53.
Barsbold R. and Osmólska H. 1999. The skull of Velociraptor [Theropoda] from the Late Cretaceous of Mongolia. Acta Palaeontologica Polonica, 44: 189–219.
Boughner J.C., Buchtová M., Fu K., Diewert V., Hallgrímsson B., and Richman J.M. 2007. Embryonic development of Python sebae – I: staging criteria and macroscopic skeletal morphogenesis of the head and limbs. Zoology, 110: 212–230.
Brinkman D.B. 2003. A review of nonmarine turtles from the late Cretaceous of Alberta. Canadian Journal of Earth Sciences, 40: 557–571.
Brinkman, D.B., and Eberth, D.A. 2006. Turtles of the Horseshoe Canyon and Scollard formations – further evidence for a biotic response to late Cretaceous climate change. In Fossil turtle research. Edited by I.G. Danilov and J.F. Parham. Russian Journal of Herpetology. pp. 11–18.
Brochu C.A. 2003. Osteology of Tyrannosaurus rex: Insights from a nearly complete skeleton and high-resolution computed tomographic analysis of the skull. Journal of Vertebrate Paleontology, 22: 1–138.
Brown, B. 1905. The osteology of Champsosaurus cope. Memoirs of the American Museum of Natural History, 9. American Museum of Natural History, New York, N.Y. pp. 1–26.
Brusatte S.L. and Carr T.D. 2016. The phylogeny and evolutionary history of tyrannosauroid dinosaurs. Scientific Reports, 6: 20252.
Brusatte S.L., Carr T.D., Erickson G.M., Bever G.S., Norell M.A., and Olsen P.E. 2009. A long-snouted, multihorned Tyrannosaurid from the late Cretaceous of Mongolia. Proceedings of the National Academy of Sciences of the United States of America, 106: 17261–17266.
Brusatte S.L., Norell M.A., Carr T.D., Erickson G.M., Hutchinson J.R., Balanoff A.M., et al. 2010. Tyrannosaur paleobiology: new research on ancient exemplar organisms. Science, 329: 1481–1485.
Brusatte S.L., Carr T.D., and Norell M.A. 2012. The Osteology of Alioramus, A Gracile and Long-Snouted Tyrannosaurid (Dinosauria: Theropoda) from the Late Cretaceous of Mongolia. Bulletin of the American Museum of Natural History, 366: 1–197.
Brusatte S.L., Averianov A., Sues H.-D., Muir A., and Butler I.B. 2016a. New tyrannosaur from the mid-Cretaceous of Uzbekistan clarifies evolution of giant body sizes and advanced senses in tyrant dinosaurs. Proceedings of the National Academy of Sciences, 113: 3447–3452.
Brusatte S.L., Carr T.D., Williamson T.E., Holtz T.R., Hone D.W.E., and Williams S.A. 2016b. Dentary groove morphology does not distinguish ‘Nanotyrannus’ as a valid taxon of tyrannosauroid dinosaur. Comment on: “Distribution of the dentary groove of theropod dinosaurs: Implications for theropod phylogeny and the validity of the genus Nanotyrannus Bakker et al., 1988”. Cretaceous Research, 65: 232–237.
Burnham D.A., Derstler K.L., Currie P.J., Bakker R.T., Zhou Z., and Ostrom J.H. 2000. Remarkable new birdlike dinosaur (Theropoda: Maniraptora) from the Upper Cretaceous of Montana. University of Kansas Paleontological Contributions, 13: 1–14.
Butler P.M. 1995. Ontogenetic aspects of dental evolution. The International journal of Developmental Biology, 39: 25–34.
Carpenter K. 1982. Baby dinosaurs from the Late Cretaceous Lance and Hell Creek formations and a description of a new species of theropod. Contributions to Geology, University of Wyoming, 20: 123–134.
Carr T.D. 1999. Craniofacial ontogeny in Tyrannosauridae (Dinosauria, Coelurosauria). Journal of Vertebrate Paleontology, 19: 497–520.
Carr T.D. 2010. A taxonomic assessment of the type series of Albertosaurus sarcophagus and the identity of Tyrannosauridae (Dinosauria, Coelurosauria) in the Albertosaurus bonebed from the Horseshoe Canyon Formation (Campanian–Maastrichtian, Late Cretaceous) This article is one of a series of papers published in this Special Issue on the theme Albertosaurus. Canadian Journal of Earth Sciences, 47: 1213–1226.
Carr T.D. 2020. A high-resolution growth series of Tyrannosaurus rex obtained from multiple lines of evidence. PeerJ, 8: e9192.
Carr T.D. and Williamson T.E. 2004. Diversity of late Maastrichtian Tyrannosauridae (Dinosauria: Theropoda) from western North America. Zoological Journal of the Linnean Society, 142: 479–523.
Carr T.D., Varricchio D.J., Sedlmayr J.C., Roberts E.M., and Moore J.R. 2017. A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system. Scientific Reports, 7: 44942.
Chapelle K.E.J., Fernandez V., and Choiniere J.N. 2020. Conserved in-ovo cranial ossification sequences of extant saurians allow estimation of embryonic dinosaur developmental stages. Scientific Reports, 10: 4224.
Chiappe, L.M., Norell, M.A., and Clark, J.M. 2002. The Cretaceous, short-armed Alvarezsauridae: Mononykus and its kin. In Mesozoic birds: above the heads of dinosaurs. University of California Press, Berkeley, Calif. pp. 87–120.
Chiarenza A.A., Fiorillo A.R., Tykoski R.S., McCarthy P.J., Flaig P.P., and Contreras D.L. 2020. The first juvenile dromaeosaurid (Dinosauria: Theropoda) from Arctic Alaska. PLoS One, 15: e0235078.
Currie P.J. 1987. Bird-like characteristics of the jaws and teeth of troodontid theropods (Dinosauria, Saurischia). Journal of Vertebrate Paleontology, 7: 72–81.
Currie P.J. 1995. New information on the anatomy and relationships of Dromaeosaurus albertensis (Dinosauria: Theropoda). Journal of Vertebrate Paleontology, 15: 576–591.
Currie P.J. 2003a. Cranial anatomy of tyrannosaurid dinosaurs from the Late Cretaceous of Alberta, Canada. Acta Palaeontologica Polonica, 48: 191–226.
Currie P.J. 2003b. Allometric growth in tyrannosaurids (Dinosauria: Theropoda) from the Upper Cretaceous of North America and Asia. Canadian Journal of Earth Sciences, 40: 651–665.
Currie P.J. 2016. Dinosaur of the Gobi: following in the footsteps of the Polish-Mongolian expeditions. Paleontologica Polonica, 67: 83–100.
Currie P.J. and Evans D.C. 2020. Cranial anatomy of new specimens of Saurornitholestes langstoni (Dinosauria, Theropoda, Dromaeosauridae) from the dinosaur park formation (Campanian) of Alberta. The Anatomical Record. 303: 691–715.
Currie, P.J., Rigby, J.K., and Sloan, R.E., 1990. Theropod teeth from the Judith River Formation of southern Alberta, Canada. In Dinosaur systematics, 1st edition. Edited by K. Carpenter and P.J. Currie. Cambridge University Press. pp. 107–126.
Currie P.J., Godfrey S.J., and Nessov L. 1993. New caenagnathid (Dinosauria: Theropoda) specimens from the Upper Cretaceous of North America and Asia. Canadian Journal of Earth Sciences, 30: 2255–2272.
DeMar D.G., Conrad J.L., Head J.J., Varricchio D.J., and Wilson G.P. 2017. A new Late Cretaceous iguanomorph from North America and the origin of New World Pleurodonta (Squamata, Iguania). Proceedings of the Royal Society B: Biological Sciences, 284: 20161902.
Dewaele L., Tsogtbaatar K., Barsbold R., Garcia G., Stein K., Escuillié F., and Godefroit P. 2015. Perinatal specimens of Saurolophus angustirostris (Dinosauria: Hadrosauridae), from the Upper Cretaceous of Mongolia. PLoS One, 10: e0138806.
Dixey F.A. 1881. II. On the ossification of the terminal phalanges of the digits. Proceedings of the Royal Society of London, 31: 63–71.
Dumont M., Tafforeau P., Bertin T., Bhullar B.-A., Field D., Schulp A., et al. 2016. Synchrotron imaging of dentition provides insights into the biology of Hesperornis and Ichthyornis, the “last” toothed birds. BMC Evolutionary Biology, 16: 178.
Eberth D.A. and Braman D.R. 2012. A revised stratigraphy and depositional history for the Horseshoe Canyon Formation (Upper Cretaceous), southern Alberta plains. Canadian Journal of Earth Sciences, 49: 1053–1086.
Eberth D.A. and Kamo S.L. 2019. High-precision U-Pb CA-ID-TIMS dating and chronostratigraphy of the dinosaur-rich Horseshoe Canyon Formation (Upper Cretaceous, Campanian–Maastrichtian), Red Deer River valley, Alberta, Canada. Canadian Journal of Earth Sciences, 56: 1041–1051.
Eberth D.A., Evans D.C., Brinkman D.B., Therrien F., Tanke D.H., Russell L.S., and Sues H. 2013. Dinosaur biostratigraphy of the Edmonton Group (Upper Cretaceous), Alberta, Canada: evidence for climate influence. Canadian Journal of Earth Sciences, 50: 701–726.
Erickson G.M., Makovicky P.J., Currie P.J., Norell M.A., Yerby S.A., and Brochu C.A. 2004. Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs. Nature, 430: 772–775.
Erickson G.M., Zelenitsky D.K., Kay D.I., and Norell M.A. 2017. Dinosaur incubation periods directly determined from growth-line counts in embryonic teeth show reptilian-grade development. Proceedings of the National Academy of Sciences, 114: 540–545.
Evans D.C., Larson D.W., and Currie P.J. 2013. A new dromaeosaurid (Dinosauria: Theropoda) with Asian affinities from the latest Cretaceous of North America. Naturwissenschaften, 100: 1041–1049.
Fastovsky D.E., Weishampel D.B., Watabe M., Barsbold R., Tsogtbaatar K., and Narmandakh P. 2011. A nest of Protoceratops andrewsi (Dinosauria, Ornithischia). Journal of Paleontology, 85: 1035–1041.
Ferguson, M.W. 1985. Reproductive biology and embryology of the crocodilians. In Biology of the reptilia. Edited by C. Gans, F.S. Billet, and P.F.A. Manderson. Wiley and Sons, New York, N.Y. pp. 329–491.
Field D.J., Hanson M., Burnham D., Wilson L.E., Super K., Ehret D., et al. 2018. Complete Ichthyornis skull illuminates mosaic assembly of the avian head. Nature, 557: 96–100.
Fiorillo A.R. and Tykoski R.S. 2014. A diminutive new tyrannosaur from the top of the world. PLoS One, 9: e91287.
Fowler D.W., Wilson J.P., Freedman Fowler E.A., Noto C.R., Anduza D., and Horner J.R. 2020. Trierarchuncus prairiensis gen. et sp. nov., the last alvarezsaurid: Hell Creek Formation (uppermost Maastrichtian), Montana. Cretaceous Research, 116: 104560.
Fröbisch N.B. 2008. Ossification patterns in the tetrapod limb - conservation and divergence from morphogenetic events. Biological Reviews, 83: 571–600.
Funston G.F. and Currie P.J. 2014. A previously undescribed caenagnathid mandible from the late Campanian of Alberta, and insights into the diet of Chirostenotes pergracilis (Dinosauria: Oviraptorosauria). Canadian Journal of Earth Sciences, 51: 156–165.
Funston G.F. and Currie P.J. 2016. A new caenagnathid (Dinosauria: Oviraptorosauria) from the Horseshoe Canyon Formation of Alberta, Canada, and a reevaluation of the relationships of Caenagnathidae. Journal of Vertebrate Paleontology, 36: e1160910.
Funston G.F. and Currie P.J. 2018a. The first record of dinosaur eggshell from the Horseshoe Canyon Formation (Maastrichtian) of Alberta, Canada. Canadian Journal of Earth Sciences, 55: 436–441.
Funston G.F. and Currie P.J. 2018b. A small caenagnathid tibia from the Horseshoe Canyon Formation (Maastrichtian): Implications for growth and lifestyle in oviraptorosaurs. Cretaceous Research, 92: 220–230.
Funston G.F., Mendonca S.E., Currie P.J., and Barsbold R. 2018. Oviraptorosaur anatomy, diversity and ecology in the Nemegt Basin. Palaeogeography, Palaeoclimatology, Palaeoecology, 494: 101–120.
Funston G.F., Currie P.J., Ryan M.J., and Dong Z.-M. 2019. Birdlike growth and mixed-age flocks in avimimids (Theropoda, Oviraptorosauria). Scientific Reports, 9: 18816.
Funston G.F., Wilkinson R.D., Simon D.J., Leblanc A.H., Wosik M., and Currie P.J. 2020. Histology of Caenagnathid (Theropoda, Oviraptorosauria) dentaries and implications for development, ontogenetic edentulism, and taxonomy. The Anatomical Record, 303: 918–934.
Gao K. and Fox R.C. 1996. Taxonomy and evolution of Late Cretaceous lizards (Reptilia: Squamata) from Western Canada. Bulletin of the Carnegie Museum of Natural History, 33: 1–107.
Gray D.J., Gardner E., and O'Rahilly R. 1957. The prenatal development of the skeleton and joints of the human hand. American Journal of Anatomy, 101: 169–223.
Gregorovičová M., Zahradnicek O., Tucker A.S., Velensky P., and Horacek I. 2012. Embryonic development of the monitor lizard, Varanus indicus. Amphibia-Reptilia, 33: 451–468.
Gregorovičová M., Kvasilová A., and Sedmera D. 2018. Ossification pattern in forelimbs of the Siamese Crocodile (Crocodylus siamensis): similarity in ontogeny of carpus among crocodylian species. The Anatomical Record. 301: 1159–1168.
Hammer O., Harper D.A.T., and Ryan P.D. 2001. PAST: paleontological statistics software package for education and data analysis. Palaeontologia Electronica, 4: 1–9.
Han M., Yang X., Lee J., Allan C.H., and Muneoka K. 2008. Development and regeneration of the neonatal digit tip in mice. Developmental Biology, 315: 125–135.
Hanai T. and Tsuihiji T. 2019. Description of tooth ontogeny and replacement patterns in a juvenile Tarbosaurus bataar (Dinosauria: Theropoda) using CT-scan data. The Anatomical Record, 302: 1210–1225.
Harris M.P., Hasso S.M., Ferguson M.W.J., and Fallon J.F. 2006. The development of Archosaurian first-generation teeth in a chicken mutant. Current Biology, 16: 371–377.
Hendrickx C., Mateus O., Araújo R., and Choiniere J. 2019. The distribution of dental features in non-avian theropod dinosaurs: Taxonomic potential, degree of homoplasy, and major evolutionary trends. Palaeontologia Electronica.
Hirsch K.F. and Quinn B. 1990. Eggs and Eggshell Fragments from the Upper Cretaceous Two Medicine Formation of Montana. Journal of Vertebrate Paleontology, 10: 491–511.
Holtz T.R. 1994. The phylogenetic position of the Tyrannosauridae: implications for theropod systematics. Journal of Paleontology, 68: 1100–1117.
Holtz, T.R. 2004. Tyrannosauroidea. In The dinosauria Second Edition. Edited by D.B. Weishampel, P. Dodson, and H. Osmólska. University of California Press, Berkeley, Calif. pp. 111–136.
Hone D.W.E., Farke A.A., Watabe M., Shigeru S., and Tsogtbaatar K. 2014. A new mass mortality of juvenile Protoceratops and size-segregated aggregation behaviour in juvenile non-avian dinosaurs. PLoS One, 9: e113306.
Horner J.R. 1982. Evidence of colonial nesting and “site fidelity” among ornithischian dinosaurs. Nature, 297: 675–676.
Horner, J.R., and Currie, P.J. 1994. Embryonic and neonatal morphology and ontogeny of a new species of Hypacrosaurus (Ornithischia, Lambeosauridae) from Montana and Alberta. In Dinosaur eggs and babies. Edited by K. Carpenter, K.F. Hirsch, and J.R. Horner. Cambridge University Press, New York, N.Y. pp. 312–336.
Horner J.R. and Padian K. 2004. Age and growth dynamics of Tyrannosaurus rex. Proceedings of the Royal Society B: Biological Sciences, 271: 1875–1880.
Horner J.R. and Weishampel D.B. 1988. A comparative embryological study of two ornithischian dinosaurs. Nature, 332: 256–257.
Horner J.R., De Ricqlès A., and Padian K. 2000. Long bone histology of the hadrosaurid dinosaur Maiasaura peeblesorum : growth dynamics and physiology based on an ontogenetic series of skeletal elements. Journal of Vertebrate Paleontology, 20: 115–129.
Horner J.R., Goodwin M.B., and Myhrvold N. 2011. Dinosaur census reveals abundant tyrannosaurus and rare ontogenetic stages in the upper cretaceous hell creek formation (Maastrichtian), Montana, USA. PLoS ONE, 6: e16574.
Hu H., O'Connor J.K., McDonald P.G., and Wroe S. 2020. Cranial osteology of the Early Cretaceous Sapeornis chaoyangensis (Aves: Pygostylia). Cretaceous Research, 113: 104496.
Jackson K. 2002. Post-ovipositional development of the monocled cobra, Naja kaouthia (Serpentes: Elapidae). Zoology, 105: 203–214.
Kundrát M., Cruickshank A.R.I., Manning T.W., and Nudds J. 2007. Embryos of therizinosauroid theropods from the Upper Cretaceous of China: diagnosis and analysis of ossification patterns: Therizinosauroid embryos from China. Acta Zoologica, 89: 231–251.
Lambe, L.M. 1917. The cretaceous theropodus dinosaur gorgosaurus. Government Printing Bureau.
Larson D.W. and Currie P.J. 2013. Multivariate analyses of small theropod dinosaur teeth and implications for paleoecological turnover through time. PLoS One, 8: e54329.
LeBlanc A.R.H., Brink K.S., Cullen T.M., and Reisz R.R. 2017. Evolutionary implications of tooth attachment versus tooth implantation: A case study using dinosaur, crocodilian, and mammal teeth. Journal of Vertebrate Paleontology, 37: e1354006.
Loewen M.A., Irmis R.B., Sertich J.J.W., Currie P.J., and Sampson S.D. 2013. Tyrant dinosaur evolution tracks the rise and fall of late cretaceous oceans. PLoS One, 8: e79420.
Longrich N. 2008. A new, large ornithomimid from the cretaceous dinosaur park formation of Alberta, Canada: implications for the study of dissociated dinosaur remains. Palaeontology, 51: 983–997.
Longrich N. 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research, 30: 161–177.
Longrich N.R. and Currie P.J. 2009. Albertonykus borealis, a new alvarezsaur (Dinosauria: Theropoda) from the Early Maastrichtian of Alberta, Canada: implications for the systematics and ecology of the Alvarezsauridae. Cretaceous Research, 30: 239–252.
Lorenz, J.C., and Gavin, W. 1984. Geology of the two medicine formation and the sedimentology of a dinosaur nesting ground. In Field conference Northwestern Montana. Montana Geological Society. pp. 175–187.
Lü J., Currie P.J., Xu L., Zhang X., Pu H., and Jia S. 2013. Chicken-sized oviraptorid dinosaurs from central China and their ontogenetic implications. Naturwissenschaften, 100: 165–175.
Lü J., Yi L., Brusatte S.L., Yang L., Li H., and Chen L. 2014. A new clade of Asian late cretaceous long-snouted tyrannosaurids. Nature Communications, 5: 3788.
Macdonald I. and Currie P.J. 2019. Description of a partial Dromiceiomimus (Dinosauria: Theropoda) skeleton with comments on the validity of the genus. Canadian Journal of Earth Sciences, 56: 129–157.
Mallon J.C. and Brinkman D.B. 2018. Basilemys morrinensis, a new species of nanhsiungchelyid turtle from the Horseshoe Canyon Formation (Upper Cretaceous) of Alberta, Canada. Journal of Vertebrate Paleontology, 38: e1431922.
Mallon J.C., Bura J.R., Schumann D., and Currie P.J. 2020. A problematic Tyrannosaurid (Dinosauria: Theropoda) skeleton and its implications for Tyrannosaurid diversity in the Horseshoe Canyon Formation (Upper Cretaceous) of Alberta. The Anatomical Record, 303: 673–690.
Maxwell E.E. 2008a. Comparative embryonic development of the skeleton of the domestic turkey (Meleagris gallopavo) and other galliform birds. Zoology, 111: 242–257.
Maxwell E.E. 2008b. Ossification sequence of the avian order anseriformes, with comparison to other precocial birds. Journal of Morphology, 269: 1095–1113.
Maxwell E.E. 2009. Comparative ossification and development of the skull in palaeognathous birds (Aves: Palaeognathae). Zoological Journal of the Linnean Society, 156: 184–200.
Maxwell E.E. and Harrison L.B. 2008. Ossification sequence of the common tern (Sterna hirundo) and its implications for the interrelationships of the Lari (Aves, Charadriiformes). Journal of Morphology, 269: 1056–1072.
Maxwell E.E., Harrison L.B., and Larsson H.C.E. 2010. Assessing the phylogenetic utility of sequence heterochrony: evolution of avian ossification sequences as a case study. Zoology, 113: 57–66.
McFeeters B., Ryan M.J., and Cullen T.M. 2018. Positional Variation in Pedal Ungulas of North American Ornithomimids (Dinosauria, Theropoda): A Response to Brownstein (2017). Vertebrate Anatomy Morphology Palaeontology, 5.
McKeown M., Brusatte S.L., Williamson T.E., Schwab J.A., Carr T.D., Butler I.B., et al. 2020. Neurosensory and Sinus Evolution as Tyrannosauroid Dinosaurs Developed Giant Size: Insight from the Endocranial Anatomy of Bistahieversor sealeyi. The Anatomical Record, 303: 1043–1059.
Meng Q., Liu J., Varricchio D.J., Huang T., and Gao C. 2004. Palaeontology: parental care in an ornithischian dinosaur. Nature, 431: 145–146.
Mohr S.R., Acorn J.H., Funston G., and Currie P.J. 2020. An ornithurine bird coracoid from the Late Cretaceous of Alberta, Canada. Canadian Journal of Earth Sciences.
Molnar R.E. and Carpenter K. 1989. The Jordan theropod (Maastrichtian, Montana, U.S.A.) referred to the genus Aublysodon. Geobios, 22: 445–454.
Müller G.B. and Alberch P. 1990. Ontogeny of the limb skeleton in Alligator mississippiensis : Developmental invariance and change in the evolution of archosaur limbs. Journal of Morphology, 203: 151–164.
Nesbitt S.J., Denton R.K., Loewen M.A., Brusatte S.L., Smith N.D., Turner A.H., et al. 2019. A mid-Cretaceous tyrannosauroid and the origin of North American end-Cretaceous dinosaur assemblages. Nature Ecology & evolution, 3: 892–899.
Norell M.A., Wiemann J., Fabbri M., Yu C., Marsicano C.A., Moore-Nall A., et al. 2020. The first dinosaur egg was soft. Nature, 583: 406–410.
Noro M., Uejima A., Abe G., Manabe M., and Tamura K. 2009. Normal developmental stages of the Madagascar ground gecko Paroedura pictus with special reference to limb morphogenesis. Developmental Dynamics, 238: 100–109.
O’Connor J.K. and Chiappe L.M. 2011. A revision of enantiornithine (Aves: Ornithothoraces) skull morphology. Journal of Systematic Palaeontology, 9: 135–157.
O’Rahilly R., Gardner E., and Gray D.J. 1960. The Skeletal Development of the Foot. Clinical Orthopaedics and Related Research, 16: 7–14.
Ogg, J.G., and Hinnov, L.A. 2012. Cretaceous. In The geologic time scale 2012. Edited by F.M. Gradstein, J.G. Ogg, M.D. Schmitz, and G.M. Ogg. Elsevier, Amsterdam. pp. 793–853.
Osborn H.F. 1905. Article XIV – Tyrannosaurus and other Cretaceous Carnivorous Dinosaurs. Bulletin of the American Museum of Natural History, XXI: 259–265.
Owen, R. 1845. Odontography, Or, a Treatise on the Comparative Anatomy of the Teeth, Their Physiological Relations, Mode of Developement, and Microscipic Structure, in the Vertebrate Animals: Text. Bailliere.
Persons W.S., Currie P.J., and Erickson G.M. 2020. An older and exceptionally large adult specimen of Tyrannosaurus rex. The Anatomical Record, 303: 656–672.
Prieto-Marquez A. and Guenther M.F. 2018. Perinatal specimens of Maiasaura from the Upper Cretaceous of Montana (USA): insights into the early ontogeny of saurolophine hadrosaurid dinosaurs. PeerJ, 6: e4734.
Pu H., Zelenitsky D.K., Lü J., Currie P.J., Carpenter K., Xu L., et al. 2017. Perinate and eggs of a giant caenagnathid dinosaur from the Late Cretaceous of central China. Nature Communications, 8: 14952.
Rauhut O.W.M. and Fechner R. 2005. Early development of the facial region in a non-avian theropod dinosaur. Proceedings: Biological Sciences, 272: 1179–1183.
Reisz R.R., Evans D.C., Sues H.-D., and Scott D. 2010. Embryonic skeletal anatomy of the sauropodomorph dinosaur Massospondylus from the Lower Jurassic of South Africa. Journal of Vertebrate Paleontology, 30: 1653–1665.
Reisz R.R., Huang T.D., Roberts E.M., Peng S., Sullivan C., Stein K., et al. 2013. Embryology of early Jurassic dinosaur from China with evidence of preserved organic remains. Nature, 496: 210–214.
Reisz R.R., LeBlanc A.R.H., Maddin H.C., Dudgeon T.W., Scott D., Huang T., et al. 2020. Early Jurassic dinosaur fetal dental development and its significance for the evolution of sauropod dentition. Nature Communications, 11: 2240.
Rieppel O. 1992. Studies on skeleton formation in reptiles. I. The postembryonic development of the skeleton in Cyrtodactylus pubisulcus (Reptilia: Gekkonidae). Journal of Zoology, 227: 87–100.
Rieppel O. 1993a. Studies on Skeleton Formation in Reptiles. II. Chamaeleo hoehnelii (Squamata: Chamaeleoninae), with Comments on the Homology of Carpal and Tarsal Bones. Herpetologica, 49: 66–78.
Rieppel O. 1993b. Studies on skeleton formation in reptiles: Patterns of ossification in the skeleton of Chelydra serpentina (Reptilia, Testudines). Journal of Zoology, 231: 487–509.
Rieppel O. 1993c. Studies on skeleton formation in reptiles. v. Patterns of ossification in the skeleton of Alligator mississippiensis Daudin (Reptilia, Crocodylia). Zoological Journal of the Linnean Society, 109: 301–325.
Rieppel O. 1994. Studies on Skeleton Formation in Reptiles. Patterns of Ossification in the Skeleton of Lacerta agilis exigua Eichwald (Reptilia, Squamata). Journal of Herpetology, 28: 145.
Russell D.A. 1970. Tyrannosaurs from the Late Cretaceous of Western Canada. National Museum of Natural Sciences Publications in Palaeontology, 1: 1–36.
Russell D.A. 1972. Ostrich dinosaurs from the Late Cretaceous of western Canada. Canadian Journal of Earth Sciences, 9: 375–402.
Ryan M.J., Currie P.J., Gardner J.D., Vickaryous M.K., and Lavigne J.M. 1998. Baby hadrosaurid material associated with an unusually high abundance of Troodon teeth from the Horseshoe Canyon Formation, Upper Cretaceous, Alberta, Canada. Gaia, 15: 123–133.
Sampson S.D. 1995. Two new horned dinosaurs from the Upper Cretaceous Two Medicine Formation of Montana; with a phylogenetic analysis of the Centrosaurinae (Ornithischia: Ceratopsidae). Journal of Vertebrate Paleontology, 15: 743–760.
Schott R.K. and Evans D.C. 2016. Cranial variation and systematics of Foraminacephale brevis gen. nov. and the diversity of pachycephalosaurid dinosaurs (Ornithischia: Cerapoda) in the Belly River Group of Alberta, Canada. Zoological Journal of the Linnean Society.
Schwarz D., Ikejiri T., Breithaupt B.H., Sander P.M., and Klein N. 2007. A nearly complete skeleton of an early juvenile diplodocid (Dinosauria: Sauropoda) from the Lower Morrison Formation (Late Jurassic) of north central Wyoming and its implications for early ontogeny and pneumaticity in sauropods. Historical Biology, 19: 225–253.
Sharpey-Schafer E.A. and Dixey F.A. 1880. V. Preliminary note on the ossification of the terminal phalanges of the digits. Proceedings of the Royal Society of London, 30: 550–550.
Simon D.J., Varricchio D.J., Jin X., and Robison S.F. 2019. Microstructural overlap of Macroelongatoolithus eggs from Asia and North America expands the occurrence of colossal oviraptorosaurs. Journal of Vertebrate Paleontology, 38: e1553046.
Smith R.J. 2009. Use and misuse of the reduced major axis for line-fitting. American Journal of Physical Anthropology, 140: 476–486.
Sternberg C.M. 1932. Two new theropod dinosaurs from the Belly River Formation of Alberta. The Canadian Field-Naturalist, 46: 99–105.
Sues H.-D. 1997. On Chirostenotes, a Late Cretaceous oviraptorosaur (Dinosauria: Theropoda) from western North America. Journal of Vertebrate Paleontology, 17: 698–716.
Tsuihiji T., Watabe M., Tsogtbaatar K., Tsubamoto T., Barsbold R., Suzuki S., et al. 2011. Cranial osteology of a juvenile specimen of Tarbosaurus bataar (Theropoda, Tyrannosauridae) from the Nemegt Formation (Upper Cretaceous) of Bugin Tsav, Mongolia. Journal of Vertebrate Paleontology, 31: 497–517.
Varricchio D.J. 1993. Bone microstructure of the Upper Cretaceous theropod dinosaur Troodon formosus. Journal of Vertebrate Paleontology, 13: 99–104.
Varricchio, D.J. 2001. Late Cretaceous oviraptorosaur (Theropoda) dinosaurs from Montana. In Mesozoic vertebrate life. Edited by D.H. Tanke and K. Carpenter. Indiana University Press, Bloomington. pp. 42–57.
Varricchio D.J. and Chiappe L.M. 1995. A new enantiornithine bird from the Upper Cretaceous Two Medicine Formation of Montana. Journal of Vertebrate Paleontology, 15: 201–204.
Varricchio D.J., Horner J.R., and Jackson F.D. 2002. Embryos and eggs for the Cretaceous theropod dinosaur Troodon formosus. Journal of Vertebrate Paleontology, 22: 564–576.
Varricchio D.J., Kundrát M., and Hogan J. 2018. An intermediate incubation period and primitive brooding in a theropod dinosaur. Scientific Reports, 8: 12454.
Vieira L.G., Santos A.L.Q., Lima F.C., Mendonça, Menezes L.T., and Sebben A. 2016. Ontogeny of the Appendicular Skeleton in Melanosuchus niger (Crocodylia: Alligatoridae). Zoological Science, 33: 372–383.
Voris J.T., Zelenitsky D.K., Therrien F., and Currie P.J. 2019. Reassessment of a juvenile Daspletosaurus from the Late Cretaceous of Alberta, Canada with implications for the identification of immature tyrannosaurids. Scientific Reports, 9: 17801.
Wang S., Zhang S., Sullivan C., and Xu X. 2016. Elongatoolithid eggs containing oviraptorid (Theropoda, Oviraptorosauria) embryos from the Upper Cretaceous of Southern China. BMC Evolutionary Biology, 16.
Wang S., Zhang Q., and Yang R. 2018. Reevaluation of the Dentary Structures of Caenagnathid Oviraptorosaurs (Dinosauria, Theropoda). Scientific Reports, 8.
Wang M., O’Connor J.K., Zhou S., and Zhou Z. 2020. New toothed Early Cretaceous ornithuromorph bird reveals intraclade diversity in pattern of tooth loss. Journal of Systematic Palaeontology, 18: 631–645.
Weishampel D.B., Fastovsky D.E., Watabe M., Varricchio D., Jackson F., Tsogtbaatar K., and Barsbold R. 2008. New oviraptorid embryos from Bugin-Tsav, Nemegt Formation (Upper Cretaceous), Mongolia, with insights into their habitat and growth. Journal of Vertebrate Paleontology, 28: 1110–1119.
Werneburg I., Hugi J., Müller J., and Sánchez-Villagra M.R. 2009. Embryogenesis and ossification of Emydura subglobosa (Testudines, Pleurodira, Chelidae) and patterns of turtle development. Developmental Dynamics, 238: 2770–2786.
Westergaard B. and Ferguson M.W.J. 1986. Development of the dentition in Alligator mississippiensis. Early embryonic development in the lower jaw. Journal of Zoology, 210: 575–597.
Westergaard B. and Ferguson M.W.J. 1987. Development of the dentition in Alligator mississippiensis. Later development in the lower jaws of embryos, hatchlings and young juveniles. Journal of Zoology, 212: 191–222.
Westergaard B. and Ferguson M.W.J. 1990. Development of the dentition in Alligator Mississippiensis: upper jaw dental and craniofacial development in embryos, hatchlings, and young juveniles, with a comparison to lower jaw development. American Journal of Anatomy, 187: 393–421.
Wilson J.P., Ryan M.J., and Evans D.C. 2020. A new, transitional centrosaurine ceratopsid from the upper cretaceous two medicine formation of Montana and the evolution of the ‘Styracosaurus -line’ dinosaurs. Royal Society Open Science, 7: 200284.
Woodward H.N., Tremaine K., Williams S.A., Zanno L.E., Horner J.R., and Myhrvold N. 2020. Growing up Tyrannosaurus rex : Osteohistology refutes the pygmy “Nanotyrannus” and supports ontogenetic niche partitioning in juvenile Tyrannosaurus. Science Advances, 6: eaax6250.
Wu X.-C., Brinkman D.B., and Russell A.P. 1996. A new alligator from the Upper Cretaceous of Canada and the relationships of early eusuchians. Palaeontology, 39: 351–375.
Xu X., Norell M.A., Kuang X., Wang X., Zhao Q., and Jia C. 2004. Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroids. Nature, 431: 680–684.
Xu X., Clark J.M., Forster C.A., Norell M.A., Erickson G.M., Eberth D.A., et al. 2006. A basal tyrannosauroid dinosaur from the Late Jurassic of China. Nature, 439: 715–718.
Zahradnicek O., Horacek I., and Tucker A.S. 2012. Tooth development in a model reptile: functional and null generation teeth in the gecko Paroedura picta. Journal of Anatomy, 221: 195–208.
Zanno L.E. and Makovicky P.J. 2011. On the earliest record of Cretaceous tyrannosauroids in western North America: implications for an Early Cretaceous Laurasian interchange event. Historical Biology, 23: 317–325.
Zanno L.E. and Makovicky P.J. 2013. Neovenatorid theropods are apex predators in the Late Cretaceous of North America. Nature Communications, 4: 2827.
Zanno L.E., Varricchio D.J., O'Connor P.M., Titus A.L., and Knell M.J. 2011. A new Troodontid Theropod, Talos sampsoni gen. et sp. nov., from the Upper Cretaceous Western Interior Basin of North America. PLoS ONE, 6: e24487.
Zanno L.E., Tucker R.T., Canoville A., Avrahami H.M., Gates T.A., and Makovicky P.J. 2019. Diminutive fleet-footed tyrannosauroid narrows the 70-million-year gap in the North American fossil record. Communications Biology, 2: 64.
Zelenitsky D.K. and Hills L.V. 1996. An egg clutch of Prismatoolithus levis oosp. nov. from the Oldman Formation (Upper Cretaceous), Devil’s Coulee, southern Alberta. Canadian Journal of Earth Sciences, 33: 1127–1131.

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Published In

cover image Canadian Journal of Earth Sciences
Canadian Journal of Earth Sciences
Volume 58Number 9September 2021
Pages: 756 - 777


Received: 11 September 2020
Accepted: 17 November 2020
Version of record online: 25 January 2021


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Key Words

  1. Tyrannosauridae
  2. embryo
  3. Theropoda
  4. Cretaceous
  5. North America


  1. tyrannosauridés
  2. embryon
  3. théropodes
  4. Crétacé
  5. Amérique du Nord



Gregory F. Funston
School of GeoSciences, University of Edinburgh, Edinburgh EH9 3FE, UK.
Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada.
Mark J. Powers
Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada.
S. Amber Whitebone
Department of Biological Sciences, University of Calgary, Calgary, AB T2N 1N4, Canada.
Stephen L. Brusatte
School of GeoSciences, University of Edinburgh, Edinburgh EH9 3FE, UK.
John B. Scannella
Museum of the Rockies, Montana State University, Bozeman, Montana 59717, USA.
John R. Horner
Honors Program, Chapman University, Orange, California 92866, USA.
Philip J. Currie*
Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada.


P.J. Currie served as a Guest Editor; peer review and editorial decisions regarding this manuscript were handled by Kathlyn Stewart and Jordan Mallon.
This paper is part of a series of invited papers in honour of palaeontologist Dr. Dale Alan Russell (1937–2019).
Copyright remains with the author(s) or their institution(s). Permission for reuse (free in most cases) can be obtained from

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