title: Vertebral Adaptations to Large Body Size in Theropod Dinosaurs.
abstract: Rugose projections on the anterior and posterior aspects of vertebral neural spines appear throughout Amniota and result from the mineralization of the supraspinous and interspinous ligaments via metaplasia, the process of permanent tissue-type transformation. In mammals, this metaplasia is generally pathological or stress induced, but is a normal part of development in some clades of birds. Such structures, though phylogenetically sporadic, appear throughout the fossil record of non-avian theropod dinosaurs, yet their physiological and adaptive significance has remained unexamined. Here we show novel histologic and phylogenetic evidence that neural spine projections were a physiological response to biomechanical stress in large-bodied theropod species. Metaplastic projections also appear to vary between immature and mature individuals of the same species, with immature animals either lacking them or exhibiting smaller projections, supporting the hypothesis that these structures develop through ontogeny as a result of increasing bending stress subjected to the spinal column. Metaplastic mineralization of spinal ligaments would likely affect the flexibility of the spinal column, increasing passive support for body weight. A stiff spinal column would also provide biomechanical support for the primary hip flexors and, therefore, may have played a role in locomotor efficiency and mobility in large-bodied species. This new association of interspinal ligament metaplasia in Theropoda with large body size contributes additional insight to our understanding of the diverse biomechanical coping mechanisms developed throughout Dinosauria, and stresses the significance of phylogenetic methods when testing for biological trends, evolutionary or not.
authors.affiliation: Department of Earth Sciences, Montana State University, Bozeman, MT, 59717, United States of America.|Department of Paleontology, Museum of the Rockies, Bozeman, MT, 59717, United States of America.
authors.forename: John P
authors.initials: JP
authors.lastname: Wilson
authors.affiliation: Department of Earth Sciences, Montana State University, Bozeman, MT, 59717, United States of America.|Department of Paleontology, Museum of the Rockies, Bozeman, MT, 59717, United States of America.
authors.forename: D Cary
authors.initials: DC
authors.lastname: Woodruff
authors.affiliation: Department of Earth Sciences, Montana State University, Bozeman, MT, 59717, United States of America.|Department of Paleontology, Museum of the Rockies, Bozeman, MT, 59717, United States of America.
authors.forename: Jacob D
authors.initials: JD
authors.lastname: Gardner
authors.affiliation: Department of Earth Sciences, Montana State University, Bozeman, MT, 59717, United States of America.|Department of Paleontology, Museum of the Rockies, Bozeman, MT, 59717, United States of America.
authors.forename: Holley M
authors.initials: HM
authors.lastname: Flora
authors.affiliation: Department of Earth Sciences, Montana State University, Bozeman, MT, 59717, United States of America.|Department of Paleontology, Museum of the Rockies, Bozeman, MT, 59717, United States of America.
authors.forename: John R
authors.initials: JR
authors.lastname: Horner
authors.affiliation: Department of Earth Sciences, Montana State University, Bozeman, MT, 59717, United States of America.|Department of Paleontology, Museum of the Rockies, Bozeman, MT, 59717, United States of America.|Department of Microbiology and Immunology, Montana State University, Bozeman, MT, 59717, United States of America.
authors.forename: Chris L
authors.initials: CL
authors.lastname: Organ
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D049628:Body Size; D025061:Dinosaurs / Q000033:anatomy & histology*; D005269:Femur / Q000033:anatomy & histology; D008023:Ligaments, Articular / Q000033:anatomy & histology; D016013:Likelihood Functions; D010802:Phylogeny; D013131:Spine / Q000033:anatomy & histology*