We know that Spinosaurus was one of the biggest of the predatory dinosaurs and one of the largest land predators of all time, but because we only have the skeletons, understanding exactly how heavy dinosaurs were is tricky. Some people say Spinosaurus was the largest predator ever to walk on Earth. Others believe it was a fight between Tyrannosaurus rex, Giganotosaurus and Spinosaurus for that top title.
There’s another question about Spinosaurus and that is we still don’t really know what its body looked like … was it two-legged or four-legged? And if it was four-legged, how did it walk with such big claws? Did it walk on its knuckles or wrists or on the palms? The truth is that we just don’t know. Yet.
Evolution isn’t a person, obviously. It’s a force of nature. But if you were to imagine it as a person, then it would be an artist who ‘recycled’ ideas again and again, rarely creating anything new. Lots of different animals evolve similar adaptations, which allow them to do the same thing. Spinosaurus is a good example. Even though Spinosaurus and crocodiles were not closely related, their skulls looked very similar.
Both types of predator hunted in the water, so shared lots of details on the skull. If it works for one animal, why change it?
1. We don’t have a complete Spinosaurus skull yet but we do have pieces. We also have a more complete skull from the closely related Irritator and can use it to predict things. Based on these fossils, we think the Spinosaurus skull was about 1.75m in length. That’s massive! Get someone to measure you and then see how big you would be compared to a Spinosaurus skull.
2. There was a small, bumpy-looking crest at the top of the snout, in front of the eyes.
3. Looking at the little pits at the end of the snout, it appears that they are not little pits but little holes that go all the way through to the other side of the bone. Although we aren’t certain, they could have been pressure sensors. We think that when Spinosaurus held its snout in the water, it could feel the tiny vibrations made by prey, just like crocodiles and alligators do.
4. The long skull had a narrow snout with a rounded tip, which allowed more teeth to be attached. On each side of the upper jaw, there were six or seven teeth at the end of the jaw and then another 12 on each side. The second and third teeth were much bigger, followed by smaller teeth then larger teeth again. Large teeth in the lower jaw helped fill this space, making it perfect for grabbing slippery fish.
5. When researchers studied the strengths and weaknesses in the skull of Spinosaurus, they found that it wasn’t as strong as it might have been. They compared it to the skull of other spinosaurs, such as Baryonyx, and to living members of the crocodile family. Although it was a very strong skull for biting down, it couldn’t twist very much. This means that Spinosaurus would not have eaten other dinosaurs, as they would have struggled more than fish and could have caused serious injury.
One of the biggest puzzles in palaeontology is the incomplete fossil record. If only part of a skeleton is found, then how is a scientist ever to understand fully what that animal was like? We can have a good idea certainly, but it will always involve guesswork (even if it’s backed up by good science). It’s a bit like receiving a 500-piece jigsaw as a present, but when you open the box, only 25 bits are there. Okay, you might get an idea of what the finished picture should look like but it won’t be easy. This is the problem with many dinosaurs but especially with Spinosaurus. This predator has caused so many arguments, because we only have some of the bones. It’s a theropod that is being updated all the time.
1. Spinosaurus was most famous for the huge row of spines running down its back.
These spines were really long bits of bone on the top of the vertebrae. Some of these spines could be as much as 1.65m in length. You have small spines on some of your vertebrae but they are around 2cm long – over 80 times shorter than those Spinosaurus spines.
2. Spinosaurus had heavy, dense bones.
Theropod dinosaurs had lots in common with each other. One thing they nearly all had was lightweight bones that were air-filled (like honeycomb). Animals such as Tyrannosaurus rex and Allosaurus (and even the birds alive today) had bones like this. Spinosaurus was different, as it had heavy, dense bones. Aquatic animals such as whales, dolphins and manatees have heavy bones too, to help make sure they don’t always float to the surface. The heavy leg bones of Spinosaurus are a clue that it spent a lot of time in the water.
3. The skull had a long, narrow snout with long and sharp, rounded teeth.
While the rest of the body was pretty weird, the head looked like a huge crocodile skull had been stuck on top. The skull had a long, narrow snout with long and sharp, rounded teeth – perfect for catching and holding on to fast, slippery fish.
4. Its front limbs were quite long with a claw on the first finger of each hand.
While the back limbs of Spinosaurus were fairly short, its front limbs (the arms) were quite long. It had a large claw on the first finger on each hand. Like all theropods, Spinosaurus could not twist its arms and hands so that the palms faced the ground. Instead its palms would have faced each other.
5. Spinosaurus had wide, flat feet with broad claws.
Spinosaurus was a theropod dinosaur. Theropod means ‘beast foot’ and most theropods had narrow and flexible feet. Spinosaurus, though, had wide, flat feet with broad claws. These would have been rubbish for running and chasing prey but perfect for paddling and swimming through the water.
6. Spinosaurus had back legs shorter than you would expect on a theropod dinosaur of this size.
Whales evolved from animals that walked on land. As they evolved during their move from land to water, their legs became shorter and shorter and at some point would have been too short for walking on land. Spinosaurus’s shorter back legs give scientists a hint that it was an aquatic predator.
Some scientists think its legs were so short, Spinosaurus couldn’t walk on land … but that is argued back and forth and the truth is that we don’t know how it walked. Even though the femur (thigh bone) was short. It had a huge ridge on it, which would have allowed for lots of big muscle attachments on the tail, meaning that Spinosaurus may have been able to use its tail to swim, in the same way a crocodile does.
Imagine an animal that weighed almost as much as four big African elephants, had a head like a giant crocodile, a body like a stretched-out T.rex and a huge sail all the way down its back. Now imagine how it walked – did it walk on four legs to support that massive weight? Was it able to move around on its two short but strong back legs? How did it balance? Did it use its front legs for support, maybe walking on its knuckles like a gorilla or on the side of its ‘hands’ to take some of that massive weight? Could it even walk on land at all, or was it forced to stay in the water, only coming out to lay eggs on land once a year? The sad news is that you won’t find the answers here, because there’s still so much we don’t know about Spinosaurus.
For years, we thought Spinosaurus was a two-legged theropod, like most of the others. That made the most sense. It almost looked as though a huge sail had been glued on to the back of a more ‘standard’ theropod like a Megalosaurus. Then, when the closely related Baryonyx was discovered and was found to have strong front limbs that could have allowed it to walk on all fours, we started to think that maybe Spinosaurus did the same. Then some scientists thought that maybe the spines supported a big energy-storing fatty hump (like we see on camels today) and that this would mean it definitely walked on four legs.
Then it was thought to be two-legged again but would have walked with crouched legs. Now it appears that it was a long and ‘stretched-out’ theropod, with a long skull, a long strong tail and short legs. In this new understanding, it’s still difficult to imagine how it walked. We all seem to have different opinions about Spinosaurus but if you ask me, I think these big predators spent most of their time in the water, where their weird bodies would have been supported and their odd shape would have allowed them to swim. I reckon they stood to hunt but the water would have helped them do this. Maybe soon we’ll know for sure.
1. How often do you think about your nostrils? How often are you grateful for them? Well, Spinosaurus had excellent nostrils. They weren’t at the end of the snout (like a crocodile) but they were high up, near the nose. This means Spinosaurus could have held the end of its snout underwater, with its mouth open, in order to catch fish. Because they were high up on the face, the nostrils would have acted like a snorkel, so the dinosaur could hunt and breathe at the same time.
2. We call the big thing on the back of a Spinosaurus a sail but it may not have been. The idea is that this row of long spines on the vertebrae was connected by skin, making a very big (and awesome-looking) sail. But because palaeontologists haven’t found any Spinosaurus skin imprint fossils yet, we can’t be 100 per cent certain.
3. It’s time to talk about the sail … it’s one of the most well-known things from any of the dinosaurs but what was it for? Remember that evolution does everything for a reason – the giraffe’s long neck, the chameleon’s funny eyes and the eagle’s hooked talons all have a purpose. The Spinosaurus sail would have been the same and helped the predator in some way. There are several possible ideas:
Thermoregulation (thur-mo reg-u-lay-shun)
This means that the sail may have been involved in controlling the body temperature. We don’t know how dinosaurs controlled their temperature. Were they warm-blooded, or endothermic (en-doh thur-mik) and made their own heat, like mammals and birds do? Were they cold-blooded, or ectothermic (ek-tow thur-mik) like reptiles and amphibians or were they somewhere between the two, like some fish such as tuna and mako sharks? Maybe Spinosaurus needed to warm its huge body, especially if it spent a lot of time in the water. If the sail had lots of small blood vessels under the skin, then maybe they could have helped warm the large dinosaur – a very early form of sunbathing. Or the sail may have been used for cooling down – using the network of blood vessels in the opposite way. Elephants use their ears like this, helping them cool down when the sun is hottest. Maybe the sail was used to cool Spinosaurus in the hot Cretaceous environment in North Africa.
Energy saving
Some scientists believe that the spines acted as an anchor for a large fatty hump. When there wasn’t much food available (during dry seasons maybe), then a fatty hump full of energy could have kept the Spinosaurus alive. Although nothing has a hump quite like this nowadays, the nearest thing would be the camel’s hump.
Hydrodynamic (hi-dro di-nam-ik) swimming
Imagine you were in control of evolution and were able to design the perfect shape for a swimming animal. You wouldn’t design a swimming animal in the shape of a brick, as that would not cut through the water. Instead, you’d make it narrow and smooth, so that it could move through the water easily and quickly. If an animal can swim like this, it can be said to be hydrodynamic. Maybe the Spinosaurus sail helped it swim better. It does look a little bit like the sailfish’s rectangular sail, which is used to stop the big predatory fish from swinging side to side when swimming. Maybe the Spinosaurus sail acted in the same way and helped this giant theropod move in the water.
Display
Many animals display to each other, either to attract a mate (like peacocks) or to warn others, ‘go away, this is my territory’ or to scare off predators. Okay, it’s safe to say that because they were possibly the biggest land predators ever, nothing tried to eat a Spinosaurus. So the sail wasn’t used to scare predators. It seems possible that these sails were for display. If they were to attract a mate, then we might expect the sail to be a different size in males and females (peacock tails and deer antlers are only used for display in males).
This leaves territory. If a stretch of river had more than one Spinosaurus hunting on it, then each would want the best place for fishing. But if they were ambush hunters, they would have needed to stay still and not move about lots, displaying. Maybe the sail was like a flag, a clear signal to others about the animal’s size and strength. Almost like a fight entirely in their heads. This territory display would work if Spinosaurus could stand on the riverbank with its mouth in the water or if the body was in the water, with only the snout and sail above the surface. I think the sail was for displaying territorially but like so many things with Spinosaurus, we still don’t know for certain.
4. The tail on a theropod dinosaur often acted as a balance for the rest of the dinosaur. Without the long and heavy tail, the animal would have been top heavy and might have toppled forwards. The tail on a Spinosaurus, though, had extra benefits. It looks as though the base of the tail was muscular and powerful, which would have allowed Spinosaurus to be a strong swimmer, using its tail to power through water.
Hunting
There is no doubt that Spinosaurus was a serious predator but how did it hunt? Looking at the bones and anatomy can give us clues, and different parts of the Spinosaurus body suggest various ways of hunting. Here are some of the ways in which Spinosaurus may have hunted:
Like a crocodile in the water
It’s almost impossible to look at the skull of a Spinosaurus and not think how similar it looks to a crocodile skull. The shape is so similar and the teeth look almost the same. It even appears to have little holes and pits in the end of the snout, which may have helped it sense vibrations and pressure changes in the water. Maybe Spinosaurus swam along in rivers, hunting large fish, just like a crocodile does.
Like a heron from the shore
As fish swim past, a heron stands absolutely still. Its head moves at lightning speed and splashes into the water to catch its prey. Maybe Spinosaurus was an ambush hunter, standing on the shore, watching the water for hours until an unsuspecting fish came by. Spinosaurus did have a very flexible neck, which could have allowed it to strike quickly. Maybe Spinosaurus stood on the riverbank in the shallow water, hunting large fish, just like a heron.
In a group like thresher sharks
It’s so easy to look at a Spinosaurus and see all the ‘big’ stuff … the crocodile-like head, the massive claws, the weird sail … but the tail might also have helped with hunting. Some aquatic hunters, such as thresher sharks, use their long flexible tails to confuse and even stun prey. Maybe Spinosaurus used its tail to hunt and may have even hunted in groups, like thresher sharks sometimes do, to make sure their hunting is even more effective.
Spinosaurus could have hunted like a crocodile, or like a heron or like a thresher shark, or possibly like all three. We don’t know, but looking at the remarkable body and anatomy of this giant aquatic predator and thinking about animals alive today may help us answer yet another Spinosaurus mystery.
