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| Sunday, 30 October 2005 |
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Junior Observer |  |
| News Business Features Editorial
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When dinosaurs ruled the world... : Marine predators
It was not only on land that animals lived during prehistoric times... While dinosaurs ruled the land, other giant reptiles took over the seas and the air. There were several kinds of streamlined reptiles which looked like the present day dolphins, crocodiles, turtles and tortoises that mastered the oceans. The most abundant in the early ages of dinosaurs were the hothosaurs which looked rather like lizards, but had flattened tails to help them swim. Some of them measured about six metres. Sea reptiles ate fish, shellfish and even each other. Mosasaurs, plesiosaurs and pliosaurs were fierce predators. Most sea reptiles had large jaws full of sharp teeth to spear slippery fish or break open tough shells. Placodonts, which looked rather like the stubby nothosaurs had peg-like front teeth for grasping shell fish. Placodonts crushed them with their back teeth, spat out the shells and swallowed the rest. But nothosaurs snapped up fish with their sharp teeth. Pliosaurs like Kronosaurus and plesiosaurs like Elasmosaurus had four strong paddles instead of feet. They moved them up and down to 'fly' through the sea in a manner similar to penguins.
The fastest reptiles in the prehistoric oceans were the Ichthyosaurs which are believed to have evolved from some kind of land-living reptile. The Ichthyosaurs, whose name means 'fish lizards' grew up to 10 metres long and had streamlined bodies like those of dolphins. An Ichthyosaurs swam by bending its back and thrusting water backwards with its fish-like tail. A tall fin on its back helped it to keep its balance, and it steered and braked with limbs that had evolved into flippers. Though Ichthyosaurs had slender snouts, they had sharp teeth which they used to crunch up prey. Mary Anning, born in 1799 in Dorset, England, who grew up to be a great fossil hunter, found the first complete fossil skeleton of a giant marine Ichthyosaur when she was only 12 years old. She also found a complete plesiosaur.
The remains of the oldest-known Ichthyosaur show a creature with a long, slim tail instead of a 'fish' tail like the one, the Ichthyosaur which evolved later had. It is believed that unlike most reptiles of today, Ichthyosaurs were born in water, not hatched or born on land. New born babies however may have had to swim up quickly to breathe air because sea reptiles could not breathe under water. Kronosaurs, which is considered to be one of the biggest sea reptiles measured nearly 17 metres in length with a huge head the size of a car! But the largest lizard so far discovered is the Mosasaurus even though it was only 10 metres long.
Prehistoric turtles and crocodiles were much bigger than their relatives found today. The largest, Archelon, was almost four metres long and had huge front paddles which powered it through the water at up to 15 kilometres an hour. Crocodiles and turtles which are among the oldest groups of living reptiles, both date back to more than 200 million years. In prehistoric times, some of their relatives even took to the air! Like most modern crocodiles, those that lived in the Age of Dinosaurs lurked in pools and rivers. They swam well and moved very fast on land. Among the crocodiles, Deinosuchus is considered the biggest to have ever lived. This giant crocodile which flourished about 75 million years ago, measured around 15-16 metres with a long head. It is believed that Protosuchus may have given rise to modern crocodiles, though it had long legs and was more active.
You may be aware that different species of animals evolved over the years. So, once nothosaurs died out early in the Age of Dinosaurs, they gave rise to a long-lasting group of swimming reptiles. They were the plesiosaurs, whose name means 'near lizards'. Plesiosaurs, which were big sea reptiles had broader bodies than nothosaurs. Some had long necks, and others short necks. Their tails were short and not much use for swimming. They rowed along, using their broad, flat flippers as oars. Plesiosaurs steered to one side by pushing one 'oar' forward and pulling another backward. The short-necked Plesiosaurs were called Pliosaurs. These creatures had long flippers and powerful jaws and could swim faster than their long-necked relatives. They could also dive to hunt for food.
The long-necked Plesiosaurs like the Elasmosaurus may not have been able to dive because evidence reveals that these reptiles could not lift their flippers higher than their hips and shoulders. Even though pliosaurs largely hunted relatives of the octopus, experts are of the view that Kronosaurs may have even hunted long-necked plesiosaurs. Kronosaurs was a 17 metre long creature with a neck longer than most pliosaurs. Tanystropheus is also a very long-necked reptile and hunted on both land and in the sea. It snapped up flying insects as well as slippery fish. Next: Prehistoric creatures of the air. |
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