When you think of enormous reptiles from the Cretaceous period, you'd be forgiven if your first thought was T. rex. But while dinosaurs are often the star of the show, they were far from the only ones.
Take Sarcosuchus imperator, for example. Sometimes called 'super croc', this predator is not the sort of beast you'd want to bump into. It's thought that this species of crocodile, thankfully extinct, would latch onto its prey with its backwards-pointing teeth, drag it into the water to be drowned. It's possible that its prey even included dinosaurs.
How big was Sarcosuchus imperator?
Modern saltwater crocodiles are one of the most formidable predators alive today. They are the largest living species of reptile, with one of the strongest bite forces of any animal. The females grow to around 3 metres long, and the males reach a whopping 6 metres.
Saltwater crocodiles, however, are mere babies in comparison to their ancient cousin, Sarcosuchus imperator. Sarcosuchus was a true monster, with estimates of its length varying from 9.5 to 12 metres.
Stunningly, Sarcosuchus wasn't even the biggest crocodilian that ever lived. "You'd have Deinosuchus from the late Cretaceous that probably would have rivalled it in size," says Dr Mark Young, a palaeontologist at the University of Edinburgh. "You have the giant caimans that lived in the Amazonian sea. They went extinct about 5 to 10 million years ago. So they may have been the very largest crocodilians known.
"And around the same time as Sarcosuchus, there was some marine crocodiles that were probably the same size as Sarcosuchus living out in the oceans."
When and where did Sarcosuchus live?
Sarcosuchus imperator lived around 113 million years ago, in the early Cretaceous period. Most specimens have been discovered in the region we now know as Niger, West Africa.
"Sarcosuchus lived in quite a large river system. Some of the specimens are from Tunisia, suggesting they went to the river deltas," says Young, "but mainly lived in very large river systems across what would have been one continent of Africa and South America."
At the same time, this area was inhabited by coelacanths, an ancient type of lobe-finned bony fish. "You would have found these coelacanths that could have reached sort of almost great white shark-sized in these river systems," Young says.
The crocodile also shared the region with the dinosaurs Lurdusaurus, Ouranosaurus and Nigersaurus.
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What did Sarcosuchus eat?
Sarcosuchus wasn't picky in its diet, it appears. "They do seem to have been going after pretty much anything they could. By the time they reached their maximum body size, they probably would have been a predator of anything," says Young.
We don't know for sure how Sarcosuchus hunted. "That's not really clear because they're quite different from any of the living crocodilians we have today," he explains. "They start off with quite a long snout like an Indian gavial, and quite narrow. But during their life it broadens quite significantly so they end up with this really, really broad, very long, but quite flat snout, which is unlike anything we have today.
"So it's it's not really clear if they were capable of lunging out of the water and grabbing a dinosaur or if they just stuck to grabbing large fish in the rivers. It's possible once they reached really large body size, they could have done both. Though – especially when they were smaller – they probably would have stuck to grabbing fish in the river systems."
How was Sarcosuchus different from a modern crocodile?
There aren't any modern species directly descended from Sarcosuchus imperator. "It's kind of like a second cousin, twice removed," Young says. Because it's on a different branch on the tree of life, it's quite different to the species we know.
Sarcosuchus has a few skeletal differences to modern crocodiles. It didn't have the ball-and-socket joints found between each of the vertebrae you'd see in a modern croc, and its osteoderms (bony deposits on the skin) were much larger, making it much less flexible. Also, though it was undoubtedly a formidable hunter, the shape of its palate probably means it couldn't produce such a high bite force.
But what about the way it behaved? "I think the Sarcosuchus as a juvenile probably would have acted similar to the Indian gavial or the Malaysian gavial," says Young. But after that, we're not quite sure.
"What happens during [their lifetime] is the radical change in skull shape, when skull and snout broaden to such a degree that the snout looks nothing like any living crocodile," he explains. "They kind of go off on their own weird tangent. And they're doing something unique that no living crocodile does."
Mark is an evolutionary biologist and palaeontologist at the University of Edinburgh. His research is focused on the land-to-sea transition of fossil reptile groups and how species evolved to suit their new environment. Read more about reptiles:
About our expert, Dr Mark Young
Mark is an evolutionary biologist and palaeontologist at the University of Edinburgh. His research is focused on the land-to-sea transition of fossil reptile groups and how species evolved to suit their new environment.
Read more about reptiles: