There’s one dinosaur that is the most mysterious, is the cause of more debate than any other and poses many questions we still need to answer. That tricky predatory dinosaur is Spinosaurus.
The first fossils were found in Egypt in 1912 by a palaeontologist from Germany, called Ernst Stromer. They included vertebrae, a huge lower jaw, teeth and a few of the long spines that have made this species so famous. Stromer did everything a good scientist should have done. He described the fossils, took photographs and drew them in perfect detail. This was really useful, as a bomb was dropped on the museum that housed the Spinosaurus fossils in 1944, destroying them forever. Since then, more fossils have been found but not enough for us to understand Spinosaurus.
The name Spinosaurus is made up from two words, ‘spino-’ meaning spine and ‘-saurus’ meaning lizard and so far, we’re sure there was definitely one species, Spinosaurus aegyptiacus (spine lizard from Egypt). But perhaps there was a second species, Spinosaurus maroccanus (spine lizard from Morocco). Scientists don’t have enough information to be certain either way, yet.
This was one of the largest theropod dinosaurs ever, maybe the biggest. Spinosaurus was roughly the same size as massive killers such as Giganotosaurus, Carcharodontosaurus and possibly Tyrannosaurus rex. Spinosaurus was alive in the mid-Cretaceous period, between 112–93.5 million years ago.
These huge predators weighed somewhere between 7 and 20 tonnes (in fact, there’s nothing that walks on land that is this big – Spinosaurus weighed as much as three killer whales) and would have measured up to 18m long. Not only was Spinosaurus a super-sized dinosaur but it also looked different. It had a long skull with a thin snout and lots of slender teeth with sharp tips. Some scientists think it walked on its two longer back legs (although there’s an argument over that which I’ll talk about later), but it was the row of long spines running the length of its back, which made this a truly distinctive dinosaur. Some of these bony spines were up to 1.65m in length (as tall as an adult human) and there was probably skin between the spines, making one big sail. But exactly what this sail was used for was a very different matter and we’ll come to that later.
Spinosaurus was the biggest of a group of theropod dinosaurs called the spinosaurs. It was a predatory dinosaur with a long skull, similar to crocodiles. It had cone-shaped teeth that had few (or no) serrations. If you look at the skull from above, the snout ends in a rounded tip, with lots of teeth, called a rosette. This is seen in all the spinosaurs and helps palaeontologists to identify them. Fossils from spinosaurs have been found in Africa, Europe, South America and Asia.
The spinosaurs belonged to a family called Spinosauridae. These dinosaurs belong with the Megalosauridea dinosaurs in a bigger group, meaning spinosaurs such as Spinosaurus were most closely related to other theropod dinosaurs such as Megalosaurus.
The Spinosauridae group sits on the Tetanurae branch of the more complete dinosaur family tree. Look closely at the Spinosauridae and you’ll see there are two main branches in this family, the Baryonychinae and Spinosaurinae. In the first group are Suchomimus from Niger in central Africa, Ichthyovenator from Laos and Baryonyx from southern England. Both Spinosaurus from Africa and Irritator from Brazil are included in the other group, Spinosaurinae, meaning Irritator and Spinosaurus were most closely related.
Irritator (Ir-ree tay-tor) ‘irritating’
This spinosaur was found in Brazil, South America. It was about 7.5m long and weighed around a tonne. It lived about 110 million years ago, in the Early Cretaceous. It had a crest at the back of the head and, like other spinosaurs, would have eaten fish. An Irritator tooth has been found embedded in the neck vertebrae of a pterosaur, but we are not sure if the dinosaur hunted or scavenged these hunting reptiles.
The only significant Irritator fossil found so far is a skull. Realising it was possibly from a new species, the palaeontologists bought it from some collectors who were trying to sell it illegally. To make it look more complete (and more expensive), the fossil collectors had added a load of clay and plaster. When they realised this, the palaeontologists were annoyed. They were so irritated that they called this new spinosaur, Irritator.
Ichthyovenator (Ick-thee-o ven-ay-tor) ‘fish hunter’
This was one of only two types of spinosaur to be discovered in Asia and fossils have only been found in Laos. It was 7.5–9m long and weighed about 1.5 tonnes. It would have lived during the Early Cretaceous, 125–113 million years ago.
So far, all we know about Ichthyovenator comes from one fossil find, in which nine vertebrae, parts of the pelvis and a rib were discovered. Although we don’t yet have a skull, the discovery did tell the scientists something special about Ichthyovenator. Because so many vertebrae were found, it showed that this spinosaur had at least two separate sails running down its back.
Suchomimus (Soo-ko my-muss) ‘crocodile mimic’
This was an African spinosaur and fossils have been found in Niger. It was about 9m long and weighed approximately 2 tonnes. It would have lived about 125–112 million years ago in the Early Cretaceous. The main fossil specimen from which we know most about Suchomimus was from a subadult animal, meaning it would not have been fully grown.
Suchomimus is a good reminder about how closely we need to look at fossils if we want to identify differences between species. Not only are there often only small differences between species’ skeletons but also not many fossils of this dinosaur have been discovered so far. However, there are some things on the bones, such as an extra little arch in one of the bones in the snout, some slightly larger tail vertebrae, and a small hook-shaped piece of bone on the upper arm bone (the humerus), which show us this was a separate species.
Baryonyx (Ba-ree on-ix) ‘heavy claw’
This was a British spinosaur but fossils have also been found in Spain. It was 7–10m long and weighed 1–1.5 tonnes. It would have lived about 130–125 million years ago in the Early Cretaceous. It had a very large claw (about 30cm long) on the first finger on each forelimb, and a long narrow snout and jaws, which looked similar to those of a gharial crocodile from India. It also had a triangle-shaped crest at the top of the snout.
The first fossil found of Baryonyx is one of the best and most complete theropod fossils in the UK. It was the first predatory dinosaur that was shown to prey on fish – fish scales were found in the area where the stomach would have been on the fossil. Remains of a young Iguanodon were also found, but we don’t know if this means Baryonyx was a predator or scavenger of other dinosaurs.
