While dinosaurs roamed the Earth and pterosaurs ruled the sky, sea monsters called ichthyosaurs dominated the world's oceans. Ichthyosaurs were ancient reptilian predators. They first appeared about 251 million years ago during the Triassic Period. 20 million years before dinosaurs came about. True to their name, which means fish lizards in Greek, the earliest ichthyosaurs looked much like lizards with fins. Over the course of their 100 million year existence, their bodies transformed and became more akin to fish in shape.
Very fishlike in appearance, it is especially well known from Early Jurassic deposits in England. The body was streamlined; no distinct neck was present, and the head blended smoothly into the body. It propelled itself by using a well-developed fishlike tail and by undulating the body. The vertebral column, which was formed from disk like structures, bent downward into the lower lobe of the caudal, or tail, fin; the upper lobe was unsupported by bone. Early reconstructions of ichthyosaurs showed them with the spinal column straightened, and it was not until well-preserved evidence was found that the bent condition of the backbone became apparent. The skull and jaws of Ichthyosaurus were long and contained numerous sharp teeth.
The eyes were very large, a trait some scientists believe gave these reptiles the ability to discern large shapes, such as those of the pliosaurs, at long distances. (Pliosaurs were large carnivorous marine reptiles thought to prey on ichthyosaurs.) The nostrils were positioned far back on the top of the skull. They probably fed largely upon fish as well as other marine animals. It is unlikely that they ventured onto land, but hey, who exactly knows.
They had long narrow skulls and jaws that were lined with sharp teeth. These teeth were used to catch prey like fish and squid. Their eyes were the largest ever recorded of any animal which helped them see through the dark waters of the deep ocean. In fact one species had eyes that were over 10 inches wide. Their bodies ranged in size. Some barely reached the length of two feet. While the longest specimen was about 85 feet (25.9 meter) long. They had paddle like fins and a vertical tail which help ichthyosaurs, despite their great size, zip through water at speeds of over 22 miles per hour (35.4 Km/h). All together these qualities put ichthyosaurs at the top of the marine food chain. By the late Cretaceous Period, about 25 million years before an asteroid wiped out the dinosaurs, ichthyosaurs became extinct. Some scientist believe it may have been due to severe climate change. But the exact reason why these early sea monsters died out is still a mystery.
Related :
Dinosaurs and extinction event (Origin and end of prehistoric creatures. Life after the Extinction)
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