INJURY AND RECOVERY IN DINOSAURS: RADIOLOGY AND GEOCHEMISTRY OF PATHOLOGIES IN HADROSAUR BONES

Fossilized bones bearing partially healed pathologies attest that dinosaurs endured and recovered from a variety of osteopathy over their lifetimes. A suite of normal and pathologic hadrosaur vertebral spines from the Campanian Dinosaur Park Formation of south-central Alberta were explored radiologically and geochemically to evaluate the form of injury repair in dinosaurs. CAT scans of these fossil pathologies show abundant vascularization in calluses, annealed reset fractures, large voids within calluses, cortical bone remodeling, and compaction of trabecular bone. Early repair of bone damage in these animals produced rugose, highly vascularized calluses, which were progressively smoothed after months to years of remodeling. Thermally sensitive oxygen isotopic ratios of bone phosphate (d¹⁸O) are depleted in the rugose calluses, reflecting a 4-6°C relative temperature elevation surrounding the injury. This increase in bone temperature has been interpreted as a response to locally enhanced cellular and metabolic activity in damaged tissue and bone. Diagenetic contaminants, particularly Sr, Ba, Y, and REE, are absorbed post mortem by bone apatite during nascent fossilization. Variations of trace-element concentration within a specimen reflect differences in bone mineral density, crystallinity, and structure. In the hadrosaur specimens, pathological bone is significantly enriched in HREE (Ho-Lu) relative to normal bone, which suggests the presence of relatively coarsely crystalline bioapatite in the rapidly grown woven bone of the new callus. The living relatives of dinosaurs, crocodilians and birds, differ in their healing mechanisms and responses, particularly in healing rate and in the structure of injury repair. Crocodilians and birds phylogenetically bracket the dinosaurs, including the hadrosaurs, which therefore could be expected to share characteristics of injury repair from both groups. However, the salient features of hadrosaur bone repair--extensive vascularization, dense Haversian bone remodeling, fracture union, and locally elevated temperatures—parallel avian rather than reptilian bone healing.