High-resolution computed tomography (CT) scans through two fossilized lesions in hadrosaur bone guided paleohistological and stable-isotopic sampling to examine the stages and structures of bone repair in hadrosaurs. Two hadrosaur caudal neural spines from late Cretaceous bonebeds in Alberta, Canada, exhibit calluses produced during healing of traumatic fractures. In both CT scans and paleohistologic sections, these specimens display a combination of reptilian and non-reptilian characteristics in dinosaurian skeletal repairs. In one specimen the callus is dominated by a trabecular lattice that lacks signs of remodeling. Trabeculae in this callus are distinctively textured by clusters of densely packed, randomly oriented lacunae, two orders of magnitude larger than typical osteocyte lacunae and reminiscent of hypertrophic chondrocytes in cartilage of reptiles. The lattice represents early mineralization of callus tissue, and it preserves a δ18O value in mineral phosphate 0.6‰ lower than adjacent non-pathologic cortex, suggesting that the repair site was ∼2.5°C warmer than uninjured tissue. The elevated temperature results from locally enhanced cellular activity around the fracture, a common consequence of bone injury in vertebrates. In the second specimen, the callus has been extensively remodeled, with several areas transformed to dense secondary Haversian bone typical of modern birds. Stable oxygen isotopes in bone phosphate of this callus show no isotopic offset, indicating that this injury had progressed further through the healing process before the animal's death. High-resolution CT scans reveal tissue density and structure differences between the two lesions, suggesting that this technology could eventually be used to gauge relative healing without altering unique fossil specimens.
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Vol. 29 • No. 2