National Geographic : 2014 Oct
120 national geographic • October 2014 Stromer concluded, with evident perplexity and perhaps a bit of frustration, that the animal was “highly specialized,” without saying what it was specialized for. Spinosaurus was part of a larger mystery, sometimes called Stromer’s Riddle, that he’d first observed in North African fossils. In nearly all ancient and modern ecosystems, plant-eaters greatly outnumber meat-eaters. Yet along the northern edge of the African continent, from Stromer’s Egyptian excavations in the east to the Kem Kem beds of Morocco in the west, the fossil record suggests the opposite. Indeed, this region was inhabited by three enormous meat-eaters, each of which would have been an apex preda- tor elsewhere: swift, 40-foot-long Bahariasaurus; 40-foot Carcharodontosaurus, like an African T. rex; and Spinosaurus, perhaps biggest and certainly oddest of all. Stromer speculated that large herbivores had probably been present— what else had the carnivores eaten?—but not many of their bones had turned up yet. Other scientists have suggested the paradox is merely sampling error, caused by geological processes that mix fossils of different ages together—or by fossil hunters who preferentially select large, spectacular carnivores because they sell better. With a new Spinosaurus in hand and knowl- edge of the precise location where it had been found, Nizar Ibrahim was in a position to find a more satisfying answer to Stromer’s Riddle. At first glance, however, the new bones made the animal all the more puzzling. For starters, the surface of the dorsal spines was smooth, which meant they were unlikely to have supported a lot of soft tissue like a hump. The spines had few channels for blood vessels, so it seemed unlikely that they were used to regulate body tempera- ture, as other researchers had conjectured. The ribs were equally dense and tightly curved, cre- ating an unusual barrel-shaped torso. The neck was long, the skull enormous. But the jaws were surprisingly slender and elongated, with a pe- culiar arched snout tip speckled with tiny pits. The forelimbs and thoracic girdle were bulky, while the hind limbs were disproportionately short and slender. “Spinosaurus is incredibly front heavy,” says paleontologist Paul Sereno, Ibrahim’s postdoc- toral adviser at the University of Chicago and the discoverer of several notable North African dinosaurs, including Suchomimus, a relative of Spinosaurus with long, crocodile-like jaws. “It’s like a cross between an alligator and a sloth.” Ibrahim had a life-size image of the animal’s skull on the wall in his office that he often stared at, unfocusing his eyes and struggling to imag- ine the enormous body stretching out behind. “I tried to see all the bones, the muscles, the con- nective tissue, everything. Sometimes it was there for an instant, then it vanished, like a mirage. My brain couldn’t quite compute all that complexity.” But a computer might. Together with Simone Maganuco at the Milan museum and Tyler Keil- lor, a fossil preparator and paleoartist at the Uni- versity of Chicago, Ibrahim set about digitally reconstructing the dinosaur. They CT-scanned each bone of their specimen at the University of Chicago Medical Center and Maggiore Hos- pital in Milan, then added other body parts by The peculiarities of the creature began to make sense only when it was viewed from an entirely different perspective: as a dinosaur that spent most of its time in the water.