My Science School

                            Various reptiles have developed the ability to glide, but the pterosaurs were the only ones to develop true flight. The arms of a pterosaur were quite short, and its entire wing was supported by an enormously long fourth finger, leaving the other fingers free to function as a hand. A thin, skin-like membrane was stretched from the elongated finger to the sides of the body, and sometimes to the hind legs.

                             The whole body of the pterosaur was extremely light, with hollow bones. In several forms the head was larger than the entire body. Some pterosaurs had tails, while others were tail-less. Some fossils even show signs of hair covering the body. Many pterosaurs lived a similar life to the modern seagull and the albatross.

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                        Crocodiles are not dinosaurs, although they both evolved from the same type of reptilian ancestors at about the same time. Crocodiles have changed very little over millions of years, because their body is vet well suited to their lifestyle and has not needed to evolve. Fossil forms range from tiny crocodiles of less than 1 m up to 16 m long giants. This is more than twice as long as any crocodiles still living today.

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                            Placodus was a very large, heavily built reptile that probably lived on shellfish. It had spade-like teeth at the front of its mouth for chipping shellfish off rocks. The broad blunt teeth at the back of its mouth were used to crush the shells before the meat was swallowed. Placodus was a stocky, clumsily built animal that would have found it awkward to move about on land. Some species developed heavy armour like that of a turtle.

                    Ichthyosaurs are an interesting example of what is known as parallel evolution (when unrelated animals sharing the same habit come to look very similar). In this case, ichthyosaurs, dolphins and sharks evolved into almost the same shape. Ichthyosaur fossils are very common, and there were many different types. They all had long beaks lined with shark teeth for feeding on fish. The largest types were 10 m long. Although some other marine reptiles probably laid their eggs on beaches, the streamlined fish-like ichthyosaurs were completely aquatic and gave birth to live young. Unborn babies have been found inside their remains. One odd feature of the ichthyosaurs is the large ring of bony plates around their eyes.

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                       Mosasaurs were relatives of the modern monitor lizards, but they differed from monitors in being up to 10 m in length. Mosasaurs had a long snaky body, which was flattened to help them swim, and paddle-like limbs. These animals were so modified to suit their marine environment that they could probably not venture onto the land. They are known to have fed on ammonites, because mosasaurs teeth marks have been found on the fossil shells of these creatures. Mosasaurs died out at about the same time as the dinosaurs.

 

                              Most of the sauropods were too enormous to be successfully attacked by predators. Some of the smaller sauropods developed their own defences. Saltasaurus had body armour, while Shunasaurus had a tail club like the ankylosaurs. Shunasaurus was found in China. It was about 10 m long and weighed about 2.5 tonnes. Other sauropods could defend themselves adequately by using their enormous tail as a whip, wielded with enormous force. The largest sauropods would have reared up and trampled any predator with their front legs.

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                           Segnosaurus is an odd dinosaur that scientists have found difficult to classify. It seems to be related to the meat-eating dinosaurs, but it would not have been able to run fast and does not have the right kind of teeth for a meat-eater. Because the front legs of Segnosaurus have powerful claws, it has been suggested that this dinosaur fed on termites, like the modern anteater. Alternatively, Segnosaurus could have been a plant-eating dinosaur although it would have been the only theropod to do this.

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                                   Carnotaurus, a meat-eating theropod found in Argentina, had a number of puzzling features. It looked rather liked T. rex, but was smaller and had even tinier arms which probably had no function at all. Carnotaurus had a massive head and short horns like a bull. Its back and sides were covered with knobbly scales.

 

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                           Dinosaurs thrived on the Earth for 180 million years. Since their extinction mammals have ruled the world for just 65 million years. Together with other reptiles, dinosaurs lived in almost every available habitat and evolved into thousands of different forms. For these reasons they must be considered an extremely successful biological experiment. The experiment eventually failed only because these animals could not adapt quickly enough when conditions on Earth suddenly changed. It is interesting to speculate on how dinosaur might have developed if these mass extinctions had not taken place. Possibly they could have evolved to parallel the ways that modern mammals have developed.

                       

                           Oviraptor was a dinosaur that specialized in eating the eggs of other dinosaurs. It cracked them open with its powerful beak. Oviraptor was only the size of a modern domestic dog, but had long powerful legs for its size. It would have needed to be able to run fast to escape the dinosaur whose nest it was robbing. Oviraptor also had large hands with long claws, which it would have used to dig into dinosaur nests and remove their eggs. Some relatives of this dinosaur had strange helmet-like growths on their heads, rather like modern hornbills.

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                       A claw found in Mongolia from the hand of an unknown dinosaur measured no less than 70 cm in length. As the horny outer part of the claw was missing, it would have been even longer. Almost nothing is known about the rest of this extraordinary animal, which has been given the name of Therizinosaurus. We do know that it was a theropod, and must have been a ferocious predator.

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                             The plant-eater Ouranosaurus, a close relative of the very common Iguanodon, and many similar large dinosaurs walked mostly on two legs. Ouranosaurus was different because it had a large sail-like crest down its back. The purpose of this crest is not certain, although as this animal lived in hot regions the crest may have been used as a heat regulator. A similar dinosaur was Spinosaurus, a typical meat-eater which had a crest 1.8 m high running down its back. It was a very large predator, about 12 m long and weighing nearly four tonnes. Spinosaurus would have been rather unwieldy as a hunter, so it may have scavenged the carcasses of dead animals.

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                                 The fierce raptors shown in the film Jurassic Park actually existed, although they were not as large as the ones depicted in the film. Like Deinonychus, Velociraptor had a large ripping claw on its hind legs, and may have hunted in packs. It had a much slimmer head than Deinonychus, and probably had a less powerful bite.

 

                    Some smaller dinosaurs may have hunted in packs, like modern wolves. By working together they would have been able to kill much larger animals.

                    Deinonychus was about the size of a human adult male, and was lightly built so it could run fast.

                   This hunter had a very stiff tail, which it probably used to steer itself and change direction quickly while chasing its prey. Like other theropods, Deinonychus had very sharp teeth, and it also had powerful arms with grasping claws. The most unusual feature was a large upturned claw on its foot, which could be swivelled downwards so that it could slash its prey with its muscular hind legs. This probably killed the prey due to loss of blood.

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                        In 1983 an amateur fossil hunter found a huge claw, 35 cm long, in a Surrey clay pit. When the site was excavated, it revealed an entirely new type of meat-eating dinosaur, which has been named Baryonyx. Although this animal looked similar to other meat-eaters, it had some unique features. A huge claw was attached to each thumb, and its head looked rather like that of a modern crocodile. Fish scales were found inside the skeleton, so it is now thought that this was the only known fish-eating dinosaur.