title: First Reported Cases of Biomechanically Adaptive Bone Modeling in Non-Avian Dinosaurs.
abstract: Predator confrontation or predator evasion frequently produces bone fractures in potential prey in the wild. Although there are reports of healed bone injuries and pathologies in non-avian dinosaurs, no previously published instances of biomechanically adaptive bone modeling exist. Two tibiae from an ontogenetic sample of fifty specimens of the herbivorous dinosaur Maiasaura peeblesorum (Ornithopoda: Hadrosaurinae) exhibit exostoses. We show that these outgrowths are cases of biomechanically adaptive periosteal bone modeling resulting from overstrain on the tibia after a fibula fracture. Histological and biomechanical results are congruent with predictions derived from this hypothesis. Histologically, the outgrowths are constituted by radial fibrolamellar periosteal bone tissue formed at very high growth rates, as expected in a process of rapid strain equilibration response. These outgrowths show greater compactness at the periphery, where tensile and compressive biomechanical constraints are higher. Moreover, these outgrowths increase the maximum bending strength in the direction of the stresses derived from locomotion. They are located on the antero-lateral side of the tibia, as expected in a presumably bipedal one year old individual, and in the posterior position of the tibia, as expected in a presumably quadrupedal individual at least four years of age. These results reinforce myological evidence suggesting that Maiasaura underwent an ontogenetic shift from the primitive ornithischian bipedal condition when young to a derived quadrupedal posture when older.
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, UMR 7193, Institut des Sciences de la Terre Paris (iSTeP), 4 Place Jussieu, BC19, F-75005, Paris, France; CNRS, UMR 7193, Institut des Sciences de la Terre Paris (iSTeP), F-75005, Paris, France.
authors.forename: Jorge
authors.initials: J
authors.lastname: Cubo
authors.affiliation: Montana State University, Museum of the Rockies, 600 West Kagy Boulevard, Bozeman, Montana, 59717, United States of America; Department of Anatomy and Cell Biology, Oklahoma State University Center for Health Sciences, 1111 W. 17th St., Tulsa, OK, 74107, United States of America.
authors.forename: Holly
authors.initials: H
authors.lastname: Woodward
authors.affiliation: Small Animal Internal Medicine, Purdue University College of Veterinary Medicine, 625 Harrison Street, West Lafayette, IN, 47907, United States of America.
authors.forename: Ewan
authors.initials: E
authors.lastname: Wolff
authors.affiliation: Montana State University, Museum of the Rockies, 600 West Kagy Boulevard, Bozeman, Montana, 59717, United States of America.
authors.forename: John R
authors.initials: JR
authors.lastname: Horner
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001842:Bone and Bones / Q000473:pathology*; D025061:Dinosaurs / Q000502:physiology*; D005580:Fossils; D008124:Locomotion; D009068:Movement / Q000502:physiology*; D011187:Posture; D011235:Predatory Behavior; D013977:Tibia / Q000473:pathology