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Maiasaura biomechanical bone modeling of fractures shows posture shift with age

Ben Creisler

New in PLoS ONE:

Jorge Cubo, Holly Woodward, Ewan Wolff & John R. Horner (2015)
First Reported Cases of Biomechanically Adaptive Bone Modeling in
Non-Avian Dinosaurs.
PLoS ONE 10(7): e0131131.

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