There are lots of things that drive evolution, making a species change over time. It could be a particular habitat, such as the cold Arctic and walruses with lots of blubber to keep them warm and sensitive whiskers to hunt in cold murky waters, or feeding techniques (just think about cobras and their excellent vision and venom-injecting fangs). There’s also the competition between predator and its prey, like the cheetah with its incredible speed and the gazelle with its ability to twist and dodge when running from a predator. Sometimes what pushes evolution comes from others of your own kind. Sometimes, you need to show others just how big and how powerful you are and where your territory starts and theirs ends.
It’s afternoon in the mid Cretaceous – a long, hot sunny day, just over 97 million years ago. It’s Egypt but it looks very different to the way it does today. The land is criss-crossed with rivers, streams, swamps and estuaries. There are thick clumps of palm trees, standing along the edge of a very wide and very deep river. The water is slow-flowing and almost crystal clear, after being filtered through rock and sand for millions of years. Long, lush water plants sway in the current while pterosaurs glide over the river, young ones snapping at giant dragonflies. It looks so calm. But not for long.
A pair of huge jaws rush through the surface to snap at a young pterosaur that almost flew too close to the water. But the little flying predator swoops aside safely and goes in search of food somewhere less deadly. The huge jaws of a Spinosaurus sink beneath the surface again, a plume of spray clouding from his nostrils, making a beautiful rainbow in the sizzling heat. He dives and swims down the river in search of prey, his strong tail sweeping slowly side to side.
As he moves through the cool water, with his large sail cutting through the surface, he spies another of his kind. A female. She’s much bigger than him and has a row of thick black stripes on her huge sail. She’s resting in the shallows, with a dead sawfish between her jaws. The sawfish is large but appears tiny next to this giant aquatic dinosaur. She rips into the flesh with her powerful claws, before gulping down chunks of soft meat.
With the dry season this year lasting so long, food has been harder to catch and has made the male Spinosaurus desperate. Usually, two giant spinosaurs like this would simply look at each other to see who was the bigger and stronger – who would win the fight. But times are tough and although she is far bigger, she also has food. The male Spinosaurus swims over.
She senses him before seeing him. The delicate little ripples in the water from his body are picked up by the sensors on her snout. She looks up and arches her body, giving him a full view of her sail. It’s saying: ‘Stay away’. But he swims closer. She drops the huge sawfish in the water and opens her mouth wide – the inside is pale and shows up brightly against her dark body. Another sign to warn him off. She doesn’t want to fight him but she will if he doesn’t move away . Still he creeps forward. He wants that fish. She flicks her tail to show her power, sending clouds of sand and fine mud swirling in the water. For a moment, they lose sight of each other. The male swims forwards. He reaches the fish, the smell of blood in his nostrils. He begins to tear into it, the water around him still cloudy. The big female is nowhere to be seen. Scared off, maybe.
With a terrifying rush, she slams into him, knocking him over. As he tumbles, he opens his mouth and hisses loudly, swallowing water as he does. The huge female slips back into the deep water and swims with her body arched, showing off her size and power. The male follows, ready to fight. When food is so scarce, both predators are prepared to fight to the death. The water is deep and both giants loop in wide circles, eyeing each other. He swims at her and manages to grasp her tail with his long jaws. His sharp curved claws sink into her tail too and she lashes wildly, trying to pull away. She reaches round and her claws hook onto him, tearing into his sail. Both roll, clawing and snapping their jaws. They’re exhausted already and need to reach the surface to breathe. The female tries to break away to reach the surface but his claws are still in her tail and he’s not letting go. With one mighty sweep of her tail, she surges up, with him close behind. Both break the surface at once, gasping for breath. Filling their lungs, the dinosaurs slip underwater once more.
Here, their sails appear to shimmer and sparkle and again, she turns her body to show that impressive sail. But he’s too hungry or too stupid to heed the warning. He lunges forwards, mouth wide open. They lock jaws, sharp cone-shaped teeth cutting into each other. With their long jaws snapped shut, they push each other, wrestling to show strength now. He manages to drag his claws along her neck, cutting deeply. She’s much bigger and stronger than him but he’s faster, and being hungry has made him confident. As his yellow eyes flash brightly in the deep, clear water, he can almost taste the sawfish waiting for him. He uses his strong tail to swipe hard at her.
These giant fish hunters are not built to fight. They display to impress, using their sail, their powerful sweeping tail and their wide mouth. Fighting is too dangerous. They’re both injured. Both are weakening. She’s losing.
The huge female Spinosaurus can feel herself getting weaker. She hadn’t eaten for weeks before the sawfish and her energy is low. She needs to escape. The smaller male loosens his grip with his mouth as he tries to reposition his deadly teeth. The massive female sees her chance and bites down hard instead. He loosens his claw and they are locked mouth to mouth. He starts to turn his body but she violently twists in the opposite direction. As her teeth are locked into the upper part of the snout, her twisting puts a huge amount of force onto it. Although a Spinosaurus snout can slightly bend upwards and downwards, it can’t twist at all. She continues to roll her body through the water and the pain makes him follow in the same direction but he’s not quick enough and the force is too much. His upper jaw snaps off, near the nostrils.
He releases his claws and pushes back. As his snout sinks to the bottom of the riverbed, he rockets to the surface, in pain and short of breath. She follows him, ready to make the kill, but he uses his powerful tail and flexible neck to snake through the water and make a quick escape. He’s alive and badly injured but he’ll survive to hunt another day. He’ll have to learn how to hunt again, using only his claws but he won’t ignore a warning sign from a big female Spinosaurus next time.
Although we don’t have a Spinosaurus fossil like this, I have seen lots of Nile crocodiles with missing upper jaws. When I used to live in a national park in Uganda, I would sometimes see crocs with these terrible injuries. I never saw a fight end in this way but I used to imagine what it would have been like. Because Spinosaurus was so similar to crocodiles in many ways, maybe they may have had these same fights.