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HAVE you heard the one about the blind men and the elephant? One man feels its tail and thinks the animal is like a sturdy rope. Another touches its tusk and says, no, an elephant is like a spear, and so on. The moral of this ancient parable is that we shouldn’t assume too much from personal experience. But there is a more literal message that no scientist should ignore: unfamiliar animals with strange features are hard to understand if you can’t see the living, breathing beast.

Over the past few years, palaeontologists have been working on their own version of the parable, with one of the most fearsome animals ever at the heart of it. Look at the jaws of Spinosaurus and you might conclude it was like a crocodile. Examine its gigantic claws and it is like a bear. Its broad, flat toe bones are like those of a wading bird. What could the life of a creature with such apparently conflicting features have been like?

“It’s almost like working on an extraterrestrial,” says Nizar Ibrahim at the University of Detroit Mercy in Michigan, who is excavating the bones of one of the most complete specimens we have found. Making sense of this fantastic beast would pay dividends, because Spinosaurus might explain one of the biggest mysteries of dinosaur evolution.

Everyone agrees that Spinosaurus was a giant. We don’t have a complete skeleton, but estimates suggest it was about 15 metres long, making it the largest carnivorous dinosaur yet found (see “Diagram”).

It belonged to a dinosaur family called the spinosaurids that appeared roughly 150 million years ago. These animals had crocodile-like jaws and teeth, but lacked the sail that Spinosaurus itself had. And like many crocodiles, they probably ate fish. A spinosaurid fossil discovered 35 years ago in the UK even had partially digested scales in the space where its stomach had been. Fish was on the menu for many of the creatures that shared the world with dinosaurs, including the reptilian ichthyosaurs and plesiosaurs that patrolled the seas. But .

“Even if Spinosaurus was a terrible swimmer, it seems to have spent a lot of time in the water”

Huge jaws are the only tool a crocodile needs to catch prey, but spinosaurids also had formidable claws that were at least 30 centimetres long. They have been compared to the huge claws grizzly bears use to hook fish out of streams. But last year David Hone at Queen Mary University of London and at the University of Maryland pointed out that the animals , which makes them an unlikely precision hunting tool. Maybe the claws were actually used to dig up burrowing prey, says Hone. No one knows.

Spinosaurus arrived into this dinosaur family about 100 million years ago. The most complete skeleton of the animal was discovered in Morocco in 2008 by local fossil hunters who sold their find to rich collectors. It ended up at the Milan Natural History Museum in Italy.

Ibrahim realised how important the specimen was and tracked down the site where it had been unearthed. He and others, including Paul Sereno at the University of Chicago, are still searching it. “We’ve not actually excavated all the bones of the skeleton yet,” says Ibrahim. “Our ideas about Spinosaurus are changing right now as we add new bones.”

A published in 2014 caused a stir by suggesting Spinosaurus was weird, even for a spinosaurid. Ibrahim and Sereno’s team reported that the animal’s torso was long, its hips were weak, and its hind legs were short. What is more, it had feet like a modern web-footed shorebird, with long toe bones that had flat undersides. No other spinosaurid we know of had feet like that.

These aren’t the features of a dinosaur that chases down prey on land. Ibrahim and Sereno argued that they indicate an animal in the early stages of an evolutionary transition from land to water. The team points to similar features in the ancient four-legged ancestors of whales, which independently evolved 50 million years ago when they were still living by rivers. Like those early “walking whales”, Spinosaurus had unusually thick-walled and dense leg bones, a feature believed to reduce buoyancy and allow animals to move around more easily in water.

“The authors make a reasonable case for this animal being aquatic,” says Hans Thewissen at Northeast Ohio Medical University, who studies the early evolution of whales.

The study , however. Ibrahim and Sereno’s team also concluded that Spinosaurus might have walked on all fours, bearing some of its weight on the knuckles of its forelimbs. But only a handful of living animals knuckle-walk, and several palaeontologists thought it was a premature conclusion, especially given that the Moroccan skeleton was missing its forelimbs. Ibrahim and Sereno’s team had reconstructed them using other spinosaurid fossils.

There is also debate about how comfortable Spinosaurus was in water. The most dramatic of the animal’s features are 1.7-metre-tall bony spines projecting vertically up from its backbone. They look a lot like the spines inside a bison’s fatty hump, and 20 years ago some researchers argued . Today the consensus is that the bones supported a sail, probably used for social or sexual display.

Either way, the bony spines put a limit on Spinosaurus‘s swimming ambitions. “That’s a considerable amount of weight when you cover it with even a small amount of flesh,” says Sereno. One consequence is that the animal would have been prone to overturning when swimming.

Even if Spinosaurus was a terrible swimmer, its dense leg bones and shorebird-like feet suggest it spent a large chunk of its life wading and feeding in shallow water. “That’s arguably the most interesting thing about this animal,” says Hone. Dinosaurs dominated Earth for 135 million years, but Spinosaurus is almost the only one known to have evolved adaptations for aquatic life. That means we have the debate back-to-front: the oddity isn’t Spinosaurus‘s features, but that water-loving dinosaurs were so rare.

A further question is why Spinosaurus‘s descendants didn’t evolve into a fully aquatic dinosaur. “I’ve often wondered about this,” says Sereno.

Recently, he’s concocted a hypothesis. Dinosaurs walked with their legs vertically beneath the body. Other animals with that set-up, like horses, must undulate their bodies up and down when they swim to increase propulsive efficiency. Sereno suspects dinosaurs would have had to swim this way too. But dinosaurs’ tails were anatomically set up to thrash from side to side. Combining that with a vertically undulating torso makes for a very inefficient swimmer, says Sereno. Worse, Spinosaurus couldn’t evolve to lose the long tail because it acted as an anchor point for major leg muscles.

It is a speculative idea that Sereno hasn’t published yet, and Hone suspects it isn’t a complete explanation for the lack of aquatic dinosaurs. Whatever was going on, Spinosaurus was evolution’s best attempt to turn a dinosaur into a sea monster – but for one reason or other, it was a doomed.

This article appeared in print under the headline “Patchwork Predator”