Friday, September 12, 2014

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

Cretaceous Leviathan
The only known dinosaur adapted to life in water, Spinosaurus swam the rivers of North Africa a hundred million years ago. The massive predator lived in a region mostly devoid of large, terrestrial plant-eaters, subsisting mainly on huge fish.
Art: Davide Bonadonna. Sources: Nizar Ibrahim, University of Chicago; Cristiano Dal Sasso and Simone Maganuco, Natural History Museum of Milan

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.

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. |

A reconstruction of the skull of Spinosaurus, with known elements in blue.
Art by Davide Bonadonna.

Researchers have long debated whether dinosaurs could swim, but there has been little direct evidence for aquadinos. Some tantalizing hints have appeared, however, in claimed "swim tracks" made by the bellies of dinos in Utah and oxygen isotopes indicating possible aquatic habitats in a group of dinosaurs called spinosaurs. Now, a research team working in Morocco has found the most complete skeleton yet of a giant carnivore called Spinosaurus, very fragmentary remains of which were first discovered in 1912 in Egypt. The new fossils not only confirm that Spinosaurus was bigger than Tyrannosaurus rex, but also show that it had evolutionary adaptations—ranging from pedal-like feet to a nostril far back on the head to high bone density like that of hippos—clearly suited for swimming in lakes and rivers.

Michael Balter. 2014. Giant Dinosaur was a Terror of Cretaceous Waterways. Science. 345(6202): 1232. DOI:

Scientists Report First Semiaquatic Dinosaur, Spinosaurus
Massive Predator Was More Than 9 Feet Longer Than Largest Tyrannosaurus rex
Spinosaurus: The First Semi-Aquatic Dinosaur via @science2_0


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Spinosaurus aegyptiacus
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