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
  • Fig. 1 Femur histology of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4.

    (A) Mid-cortex of the transverse thin section of BMRP 2002.4.1. Plane-polarized light (PPL) emphasizes osteocyte lacuna density and variability in shape within the laminae, as well as longitudinal primary osteons. In CPL, there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many primary osteons (POs) have uniformly isotropic fibers with rounded osteocyte lacunae. (B) Mid-cortex of the transverse thin section of BMRP 2006.4.4. Osteocyte lacuna density and variability in shape within the laminae are evident in PPL. CPL reveals varying birefringence associated with bone fiber orientation, but there is a weak preferred fiber arrangement parallel to the transverse plane of section reflected by regional birefringence. Many POs are composed of uniformly isotropic fibers with rounded osteocyte lacunae. (C) Longitudinal section of the mid-cortex of BMRP 2006.4.4. Vascular canals appear as near-vertical, thin, dark columns. As in the transverse section, the primary laminae between POs contain variably arranged osteocyte lacunae. In CPL, the laminae are weakly isotropic (I), corresponding to the poorly organized parallel orientation of fibers in the transverse plane. The laterally compressed osteocyte lacunae in POs are embedded within a uniformly birefringent [anisotropic (AN)] matrix in CPL, indicating that the PO lamellae are longitudinally oriented parallel-fibered bone (LP). (D) On the posteromedial side of the transverse section of BMRP 2006.4.4, there is a parallel-fibered annulus located at the periosteal surface (thickness indicated with blue line). Photographed in CPL. (E) In the transverse section on the posterolateral side, the annulus shown in (D) (blue lines) is overlain by highly isotropic woven-fibered laminae.

  • Fig. 2 Tibia histology of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4.

    (A) Transverse mid-cortex thin section of BMRP 2002.4.1. Longitudinal POs are evident, and PPL emphasizes osteocyte lacuna density and variability in shape within laminae. CPL reveals varying birefringence associated with bone fiber orientation, but with a weak arrangement of fibers parallel to the transverse plane of section. Many POs are composed of highly isotropic fibers with rounded osteocyte lacunae. (B) Longitudinal thin section of the mid-cortex of BMRP 2002.4.1. Vascular canals appear as near-vertical, dark columns. Adjacent to the vascular canals, the POs contain laterally compressed osteocyte lacunae. CPL demonstrates that the laterally compressed osteocyte lacunae of POs are embedded within a uniformly birefringent matrix (anisotropic), indicating that the lamellae of POs are LP. Osteocyte lacunae orientation varies in the thin laminae between POs. In CPL, the laminae are weakly isotropic, corresponding to the weak arrangement of parallel fibers in transverse section. (C) In transverse thin section, the periosteal surface of BMRP 2006.4.4 on the anterior side consists of reticular POs within laminae of highly isotropic, woven tissue. (D) Within the anterior and anteromedial innermost cortex of BMRP 2006.4.4, in transverse thin section, six closely spaced LAGs are visible interstitially. Blue lines highlight the LAG trajectories.

  • Fig. 3 The presence of an EFS at the periosteal surface of a long bone indicates skeletal maturity, while the absence of an EFS indicates that the bone is still growing at the time of death.

    (A) An EFS composed of tightly stacked birefringent LAGs (between blue arrowheads) at the periosteal surface of an Alligator mississippiensis. (B) The EFS (between blue arrowheads) in an ostrich (Struthio camelus) is made of nearly avascular, birefringent parallel-fibered to lamellar primary tissue. (C) No EFS is present at the periosteal surface of the femur of BMRP 2002.4.1, (D) the tibia of BMRP 2002.4.1, (E) the femur of BMRP 2006.4.4, or (F) the tibia of BMRP 2006.4.4. All panels are shown in transverse thin section, with CPL.

  • Fig. 4 Examples of variable CGM (blue lines) spacing in tyrannosaurids examined for this study.

    (A) The variability of CGM spacing in the femur of BMRP 2002.4.1 and (B) the tibia of BMRP 2006.4.4 may imply that these individuals were approaching asymptotic body length. However, CGMs within the innermost cortices of much larger T. rex specimens (C) USNM PAL 555000 and (D) MOR 1128 demonstrate that the CGM spacing is not a reliable indicator of relative maturity status. All panels are shown in transverse thin section.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/6/1/eaax6250/DC1

    Supplementary Materials and Methods

    Fig. S1. Hind limb elements of BMRP 2006.4.4.

    Fig. S2. Femur and tibia histology overview of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4.

    Fig. S3. Fragmentary femur transverse thin section of BMRP 2002.4.1.

    Fig. S4. Transverse thin section histology of the right tibia of BMRP 2002.4.1.

    Fig. S5. Longitudinal thin section of BMRP 2002.4.1 tibia.

    Fig. S6. Transverse and longitudinal thin sections were produced from the left femur of BMRP 2006.4.4.

    Fig. S7. Longitudinal thin section of the left femur from BMRP 2006.4.4.

    Fig. S8. Transverse thin section of the left tibia of BMRP 2006.4.4.

    References (15, 4154)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Materials and Methods
    • Fig. S1. Hind limb elements of BMRP 2006.4.4.
    • Fig. S2. Femur and tibia histology overview of tyrannosaurid specimens BMRP 2002.4.1 and BMRP 2006.4.4.
    • Fig. S3. Fragmentary femur transverse thin section of BMRP 2002.4.1.
    • Fig. S4. Transverse thin section histology of the right tibia of BMRP 2002.4.1.
    • Fig. S5. Longitudinal thin section of BMRP 2002.4.1 tibia.
    • Fig. S6. Transverse and longitudinal thin sections were produced from the left femur of BMRP 2006.4.4.
    • Fig. S7. Longitudinal thin section of the left femur from BMRP 2006.4.4.
    • Fig. S8. Transverse thin section of the left tibia of BMRP 2006.4.4.
    • References (15, 4154)

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