National Geographic : 2014 Oct
Spinosaurus 121 MORE ONLINE ngm.com/more scanning photos from museum specimens in Milan, Paris, and elsewhere, as well as digital images of Stromer’s photographs and sketches, scaling up the remains of younger individuals to adult size in some cases. Keillor, an expert in the digital modeling program ZBrush, sculpted missing bones in ZBrush’s “digital clay,” mapping his work with scans of the same anatomy in re- lated spinosaurid dinosaurs like Suchomimus and Bar yonyx. By painstakingly shaping and spacing the 83 vertebrae in their model, they determined that an adult Spinosaurus measured 50 feet from nose to tail. There had been claims that Spino- saurus was the largest carnivore to ever walk the Earth. This confirmed it. (The largest T. rex is 40.5 feet head to tail.) Next they wrapped the skeleton in digital skin to create a dynamic model, which allowed them to estimate the animal’s center of gravity and body mass, the better to understand how it moved. Their analysis led to a remarkable con- clusion: Unlike all other predatory dinosaurs, which walked on their hind legs, Spinosaurus may have been a functional quadruped, also enlisting its heavily clawed forelimbs to walk. The peculiarities of the creature began to make real sense, however, only when Ibrahim and his colleagues viewed Spinosaurus from an entirely different perspective: as a dinosaur that spent most of its time in the water. The nostrils are set high on the skull toward the eyes, al- lowing the animal to breathe with much of its head submerged. The barrel-shaped torso re- calls dolphins and whales, and the density of its ribs and long bones is similar to that of another aquatic mammal, the sea cow. The hind legs, so oddly proportioned for walking, would have been perfect for paddling, particularly if the flat claws in its broad hind feet had been connected with webbing like a duck’s, as the researchers suspect. Its long, slender jaws and smooth, conical, croc-like teeth would have been dev- astatingly effective at snaring fish, and the pits in its snout, also present in crocs and alligators, probably housed pressure sensors to detect prey in murky water. Ibrahim imagines Spinosaurus hunting a bit like a heron, leaning forward and snapping up fish with its long muzzle. This new vision of Spinosaurus as an aquat- ic dinosaur suggests a possible solution to Stromer’s Riddle. The river along which this animal died was one of many large waterways in a vast fluvial system that occupied much of North Africa in the Cretaceous. If the carnivores here were big, so too was the aquatic life, whose remains are common in the Kem Kem depos- its: 8-foot lungfish, 13-foot coelacanths, 25-foot sawfish, and similarly outsize turtles. These ani- mals would have made healthy meals for even the largest predator, obviating the need for abun- dant large herbivores to balance the food web. All this came home to Ibrahim with full force when he saw the culminating phase of the digital dinosaur project: a life-size Spinosaurus skeleton in high-density polystyrene foam, created from the computer model in part by a 3-D printer. The skeleton is mounted in a swimming posture, which Ibrahim thinks it may have employed as much as 80 percent of the time. “I wish Ernst Stromer could see this model, which shows just how much of a specialized swimmer Spinosaurus had become. It would have made him smile.” j Bigger Than T. rex A paleontologist turns detective to find the source of mysterious bones. Watch this Nat Geo/NOVA special on November 5 at 9 p.m. TELEVISION VIDEO “ Wow, this thing could... pull me into three pieces!” —Paleontologist NIZAR IBRAHIM INTERACTIVE GRAPHIC Flesh and Bones Teeth, neck, sail, tail: See how researchers pieced together the Spinosaurus. Then take your own tour through the dinosaur’s anatomy.