Research ArticleEVOLUTIONARY BIOLOGY

Growing up Tyrannosaurus rex: Osteohistology refutes the pygmy “Nanotyrannus” and supports ontogenetic niche partitioning in juvenile Tyrannosaurus

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Science Advances  01 Jan 2020:
Vol. 6, no. 1, eaax6250
DOI: 10.1126/sciadv.aax6250

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  • RE: Growing up Tyrannosaurus rex: Osteohistology refutes the pygmy “Nanotyrannus” and supports ontogenetic niche partitioning in juvenile Tyrannosaurus
    • Alexander J. Ruger, Paleontological Technician, Black Hills Institute of Geological Research
    • Other Contributors:
      • Timothy B. Larson, Paleontological Technician, Black Hills Institute of Geological Research
      • Samuel T. Farrar, Geologist, Black Hills Institute of Geological Research
      • Peter L. Larson, President, Black Hills Institute of Geological Research

    Nanotyrannus lancensis remains a controversial taxon. Credible cases have been made (1) that specimens of this cryptic tyrannosaurid represent juvenile Tyrannosaurus rex. Woodward et al. (2020) (3) present histological data on two specimens and interpret it as a refutation of the “Nanotyrannus hypothesis.” They argue that their data support the synonymization of N. lancensis and T. rex. We question the authors’ interpretation of this data in light of morphological, taxonomic, allometric, and other histological analyses. We discuss the presence of morphologies that render this synonymization problematic, the interpretation of histology, and the comparative life histories of tyrannosaurids.

    Carr and Williamson (1) expanded on previous interpretations of CMNH 7541 and outlined a model growth series. However, several authors have described morphological problems with this hypothesis. These are summarized in Larson (2013) (2), but in brief include, but are not limited to, differences in the braincase, tooth count disparities far outside the variation seen in other tyrannosaurids and other vertebrates, differences in limb proportion between Tyrannosaurus and Nanotyrannus which do not appear to fall under the same ontogenetic controls as other tyrannosaurids, the closure of vertebral sutures showing the diminutive Nanotyrannus (BMRP 2002.4.1) at a more advanced ontogenetic stage than the second-largest (7) Tyrannosaurus (FMNH PR2081), and the differing positions and existe...

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    Competing Interests: None declared.

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