Newly-discovered 95-million-year-old fossils of the carnivorous dinosaur Spinosaurus aegyptiacus are the most compelling evidence to date of a dinosaur able to live and hunt in an aquatic environment, according to an international team of paleontologists headed by Dr Dawid Iurino of the Sapienza Universita di Roma, Italy. The remains also indicate that Spinosaurus aegyptiacus was the largest known predatory dinosaur to live on our planet, measuring about 3 meters longer than Tyrannosaurus rex.
The only known dinosaur adapted to life in water, Spinosaurus aegyptiacus swam the rivers of North Africa about 95 million years ago. Image credit: © Davide Bonadonna / National Geographic magazine.
Dr Iurino and his colleagues found that Spinosaurus aegyptiacus developed a variety of previously unknown aquatic adaptations.
These adaptations include:
– huge, slanted teeth that interlocked at the front of the snout; the conical shape and location of the teeth were well-suited for catching fish;
– neurovascular openings at the end of the snout; similar openings on crocodile and alligator snouts contain pressure receptors that enable them to sense movement in water; it’s likely these openings served a comparable function in Spinosaurus aegyptiacus;
– small nostrils located in the middle of the skull; the small size and placement of the nostrils farther back on the skull allowed this dinosaur to breathe when part of its head was in water;
– a long neck and trunk that shifted the dinosaur’s center of mass forward; this made walking on two legs on land nearly impossible, but facilitated movement in water;
– powerful forelimbs with curved, blade-like claws; these claws were ideal for hooking or slicing slippery prey;
– strong, long-boned feet and long, flat claws; unlike other predators, Spinosaurus aegyptiacus had feet similar to some shorebirds that stand on or move across soft surfaces rather than perch;
– a small pelvis and short hind legs with muscular thighs; as in the earliest whales, these adaptations were for paddling in water and differ markedly from other predatory dinosaurs that used two legs to move on land;
– loosely connected bones in the dinosaur’s tail; these bones enabled its tail to bend in a wave-like fashion, similar to tails that help propel some bony fish;
– large dorsal spines covered in skin that created a gigantic ‘sail’ on the Spinosaurus aegyptiacus’ back; the tall, thin, blade-shaped spines were anchored by muscles and composed of dense bone with few blood vessels; this suggests the sail was meant for display and not to trap heat or store fat; the sail would have been visible even when the animal entered the water;
– particularly dense bones lacking the marrow cavities typical to predatory dinosaurs; similar adaptations, which enable buoyancy control, are seen in modern aquatic animals like king penguins.
The paleontologists came to their conclusions after analyzing new fossils uncovered in the Moroccan Sahara and a partial skull and other remains housed in museum collections around the world as well as historical records and images from the first reported discovery of Spinosaurus aegyptiacus in Egypt in 1912.
The team CT scanned all of the new fossils to create a digital model of the dinosaur’s skeleton.
“We relied upon cutting-edge technology to examine, analyze and piece together a variety of fossils. For a project of this complexity, traditional methods wouldn’t have been nearly as accurate,” said Dr Simone Maganuco of the Museo di Storia Naturale di Milano, Italy, who is a co-author of a paper describing the results in the journal Science.
The team then used the digital model of Spinosaurus aegyptiacus to create an anatomically precise, life-size replica of its skeleton.
“What surprised us even more than the dinosaur’s size were its unusual proportions. We see limb proportions like this in early whales, not predatory dinosaurs,” said co-author Dr Paul Sereno of the University of Chicago.
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Nizar Ibrahim et al. Semiaquatic adaptations in a giant predatory dinosaur. Science, published online September 11, 2014; doi: 10.1126/science.1258750
