[Paleontology • 2014] Semiaquatic Adaptations in a Giant Predatory Dinosaur, Spinosaurus aegyptiacus

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 hind limbs 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.

Ibrahim, N., Sereno, P., Dal Sasso, C., Maganuco, M., Martill, D., Zouhri, S., Myhrvold, N., Iurino, D. 2014. Semiaquatic Adaptations in a Giant Predatory Dinosaur. Science.
doi: dx.doi.org/10.1126/science.1258750
http://www.sciencemag.org/content/suppl/2014/09/10/science.1258750.DC1/Ibrahim.SM.pdf

Digital skeletal reconstruction and transparent flesh outline of Spinosaurus aegyptiacus.  Color codes are used to show the origin of different parts of the digital skeletal model. Bones of the neotype and for Suchomimus tenerensis were CT-scanned, surfaced and size-adjusted before being added to the model. Color coding: red, neotype (FSAC-KK 11888); orange, Stromer’s bones; yellow, isolated bones from the Kem Kem; green, surrogate bones modeled or taken from the spinosaurids Suchomimus, Baryonyx, Irritator or Ichthyovenator; blue, inferred bones from adjacent bones. A red dot below the posterior dorsal centra shows the approximate position of the center of mass. Model by Tyler Keillor, Lauren Conroy, and Erin Fitzgerald. | phenomena.nationalgeographic.com