Skeleton of a semi-aquatic predator completes a story interrupted by bombs in WWII.
by John Timmer – Sept 11 2014,
Enlarge / Red and orange bones represent either the original Egyptian find or the new skeleton. Yellow bones come from other animals. Only the blue and green bones had to be inferred based on other species.
Model by Tyler Keillor, Lauren Conroy, and Erin Fitzgerald, Ibrahim et al., Science/AAAS
The predatory dinosaur Spinosaurus aegyptiacus isn’t famous, but it might have been. Discovered in Egypt in 1912, it had all the ingredients to make for a childhood favorite: enormous size, sharp teeth, and a huge, enigmatic sail running down its back. But the study of Spinosaurus suffered a serious interruption when the only bones of the creature happened to be underneath the payload of a British bomber targeting Munich.
Now, roughly 70 years later, Spinosaurus is back thanks to some additional samples discovered in Morocco. These, combined with images of the original skeleton and a handful of scattered bones found in the intervening years, appear to indicate the creature was a rarity for dinosaurs. It was adapted to an aquatic lifestyle and probably used its jaws and claws to snare fish.
The new skeletal remains include parts of the head, the spinal column, limbs, and extensive remains of the tail. It was found in a fossil bed called Kem Kem, which preserves the remains of a freshwater river system including various fish and sharks. The authors created a 3-D scan of the individual bones and, by filling in the gaps with bones scaled up or down from other samples or close relatives, created a complete model of the animal’s skeleton. In total, the animal appears to have been 15 meters (nearly 50 feet) long, which would make it larger than any known Tyrannosaurus skeleton.
But it wouldn’t have cut nearly as imposing a figure. The model allowed the authors to locate the animal’s center of gravity, and they found that it would be quite a bit forward of its hips. This means that, on land, Spinosaurus would have been hunched over on all fours.
The authors provide a long list of reasons to think that Spinosaurus wouldn’t have spent a lot of time on land. The nostrils have shifted back to the middle of the skull, which would have placed them where they would allow the animal to breathe without raising its head out of the water. In their place at the front of the snout is a series of passages similar to the ones crocodilians use to sense disturbances in the water. The neck had also been reworked to allow it to make vertical lunges, perhaps to snare fish.
The hindlimbs were short relative to other dinosaurs, and the pelvic bones were reduced in size, too. This could aid the animal in paddling, and the hind feet were likely flat-bottomed and could have been webbed. The large tail could swing horizontally, providing additional propulsion, again in a manner similar to crocodilians. Many of the limb bones are dense, lacking an internal cavity, which could have helped Spinosaurus maintain its stance while submerged.
While there are many comparisons to crocodilians to be made, the authors note the general outlines of Spinosaurus’ adaptations have a lot in common with those of a completely different group: mammals. The shortened, solid hind limbs have also appeared in some of the earliest ancestors of whales as they shifted to aquatic environments, and this evokes features found in present creatures like hippos.
On top of all that, the sail that’s visible in the skeletal remains is built from a series of long extensions from the spinal cord. And we’re still not sure what that’s for.
So nearly 70 years after its destruction in Munich, we finally have a more complete picture of what Spinosaurus looked like. And thanks to that, we can say a lot more about what it did: paddled through aquatic ecosystems, dining on fish.
John Timmer / John became Ars Technica’s science editor in 2007 after spending 15 years doing biology research at places like Berkeley and Cornell.
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