What Was Spinosaurus? The Dinosaur That Went Into the Water
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The largest predatory dinosaur known was described from bones dug out of the Egyptian desert in 1912, displayed in Munich, and blown to pieces by an Allied bombing raid in April 1944, so that for seventy years Spinosaurus existed only as photographs, drawings and a name. Bones found in Morocco since 2008 have rebuilt it into something no one expected: a fifteen-metre animal with a crocodile's jaws, a two-metre sail on its back, short hind legs, dense bones and a paddle-shaped tail, and the first dinosaur that seems to have hunted in the water rather than beside it. How much of its life it spent there is the liveliest argument in the field.
The bones that were lost
Ernst Stromer, a Bavarian palaeontologist, collected the first Spinosaurus from the Bahariya oasis in the Western Desert of Egypt between 1910 and 1914: a lower jaw, vertebrae with spines up to 1.65 metres tall, and fragments, from rocks about 95 million years old. He named it Spinosaurus aegyptiacus in 1915 and reconstructed a large theropod with a sail. The bones went into the Bavarian State Collection in Munich, whose director refused Stromer's request to move them to safety during the war, and on the night of 24 to 25 April 1944 the building was destroyed. Stromer's drawings and a few photographs are all that remain, and until this century they were nearly all that was known.
The animal rebuilt
Fragments turned up in Morocco's Kem Kem beds through the 1990s and 2000s, and in 2014 a team led by Nizar Ibrahim published a partial skeleton from a single individual, including hind limbs and pelvis, and a reconstruction that startled everyone: the hind legs were short and the pelvis small, so that the animal seemed poorly built for walking on two legs, and its bones were dense like a penguin's or a manatee's, an adaptation for controlling buoyancy. A tail found at the same site and described in 2020 was tall and paddle-shaped from root to tip, unlike any other dinosaur's, and in a flume it produced far more thrust than a normal theropod tail. The features assembled from Egypt and Morocco:
- •Length of 14 to 15 metres, longer than Tyrannosaurus though probably lighter
- •A long, narrow, crocodile-like snout with conical teeth for gripping fish rather than blades for cutting flesh, and pits on the snout that in crocodiles house pressure sensors
- •Nostrils set well back on the head, as in animals that keep the snout in water
- •A sail of neural spines up to two metres tall along the back, its purpose unknown, display and thermoregulation being the guesses
- •Short hind legs, dense limb bones, and a fin-like tail
- •Isotopes in the teeth showing a diet with much aquatic prey, and a habitat of rivers and deltas full of giant fish, crocodiles and sawfish
The argument
Ibrahim's team argued in 2020 that Spinosaurus was a pursuit predator that swam after prey in the rivers of Cretaceous North Africa, propelled by its tail, the first known aquatic dinosaur. Other palaeontologists have tested the claim against the physics and disagreed. A 2022 analysis of bone density across many animals found Spinosaurus in the range of divers; a 2022 study of the body's shape and buoyancy found it would have floated too high to dive, been unstable in the water and a slow swimmer, and concluded it was a wader that stood in shallows and struck like a heron, its tail perhaps for display. The two camps have exchanged papers since, and the most likely picture is between them: an animal that lived in and beside water, waded and swam as a crocodile does, ate fish and whatever else it could catch, and did not chase prey through deep river channels like a seal.
Its relatives
Spinosaurus belongs to a family of long-snouted theropods, the spinosaurids, found across the Cretaceous world: Baryonyx from a Surrey clay pit, described in 1986 with fish scales in its stomach and a great hooked claw on its thumb, Suchomimus from Niger, and Irritator from Brazil. All had the crocodile snout and the conical teeth, and all lived by water; Spinosaurus took the trend furthest. The family shows that the theropods, usually pictured as the lions and wolves of their age, also produced fish-eaters and semi-aquatic hunters, and that the ecology of a Cretaceous river was as crowded as a modern one, with a fifteen-metre dinosaur competing with crocodiles the size of buses for fish the size of cars.
The takeaway
Spinosaurus was a fifteen-metre theropod of Cretaceous North Africa with a crocodile-like snout and teeth, nostrils set back for a snout in water, a two-metre sail, short hind legs, dense bones and a paddle tail, first found in Egypt, destroyed in Munich in 1944 and rebuilt from Moroccan finds since 2014. It ate fish and lived in and beside rivers, and whether it swam after prey or waded and struck from the shallows is the argument that its unique anatomy has not yet settled.