title: Semiaquatic adaptations in a giant predatory dinosaur.
abstract: We describe adaptations for a semiaquatic lifestyle in the dinosaur Spinosaurus aegyptiacus. These adaptations include retraction of the fleshy nostrils to a position near the mid-region of the skull and an elongate neck and trunk that shift the center of body mass anterior to the knee joint. Unlike terrestrial theropods, the pelvic girdle is downsized, the hindlimbs are short, and all of the limb bones are solid without an open medullary cavity, for buoyancy control in water. The short, robust femur with hypertrophied flexor attachment and the low, flat-bottomed pedal claws are consistent with aquatic foot-propelled locomotion. Surface striations and bone microstructure suggest that the dorsal "sail" may have been enveloped in skin that functioned primarily for display on land and in water.
authors.affiliation: Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL 60637, USA. nibrahim@uchicago.edu.
authors.forename: Nizar
authors.initials: N
authors.lastname: Ibrahim
authors.affiliation: Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL 60637, USA.
authors.forename: Paul C
authors.initials: PC
authors.lastname: Sereno
authors.affiliation: Museo di Storia Naturale di Milano, Corso Venezia 55, 20121 Milan, Italy.
authors.forename: Cristiano
authors.initials: C
authors.lastname: Dal Sasso
authors.affiliation: Museo di Storia Naturale di Milano, Corso Venezia 55, 20121 Milan, Italy.
authors.forename: Simone
authors.initials: S
authors.lastname: Maganuco
authors.affiliation: School of Earth Sciences, University of Bristol, Queen's Road, Bristol, BS8 1RJ, UK.
authors.forename: Matteo
authors.initials: M
authors.lastname: Fabbri
authors.affiliation: School of Earth and Environmental Sciences, University of Portsmouth, Burnaby Road, Portsmouth, PO1 3QL, UK.
authors.forename: David M
authors.initials: DM
authors.lastname: Martill
authors.affiliation: Laboratoire de Géosciences, Faculté des Sciences Aïn Chock, Université Hassan II, Casablanca, Morocco.
authors.forename: Samir
authors.initials: S
authors.lastname: Zouhri
authors.affiliation: Intellectual Ventures, 3150 139th Avenue Southeast, Bellevue, WA 98005, USA.
authors.forename: Nathan
authors.initials: N
authors.lastname: Myhrvold
authors.affiliation: Dipartimento di Scienze della Terra, Sapienza Università di Roma, Piazzale Aldo Moro 5, 00185 Rome, Italy.
authors.forename: Dawid A
authors.initials: DA
authors.lastname: Iurino
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D001842:Bone and Bones / Q000033:anatomy & histology / Q000502:physiology / Q000648:ultrastructure; D025061:Dinosaurs / Q000033:anatomy & histology* / Q000502:physiology*; D005269:Femur / Q000033:anatomy & histology / Q000502:physiology; D020387:Food Chain; D006614:Hindlimb / Q000033:anatomy & histology / Q000502:physiology; D013550:Swimming; D013623:Tail / Q000033:anatomy & histology / Q000502:physiology; D014867:Water
chemical_list: D014867:Water