Ichthyosaurs - 'Fish Lizards'

ichthyosaurus detail

Ichthyosaurs are an extinct marine reptile thought to have first appeared on our planet around 250 million years ago and disappeared approximately 95 million years ago. The word 'ichthyosaur' comes from the Greek words 'ichthyos' meaning fish, and 'sauros' meaning lizards/reptiles, so ichthyosaurs are also known as 'fish-lizards'. They were most abundant in the Late Triassic and Early Jurassic Periods, swimming through the oceans at the same time that dinosaurs were roaming the land.

Many different species of ichthyosaur existed during their long time on Earth. The earliest ichthyosaurs were long and eel-like, but as the group evolved their body shape changed to become more fish-like. The different species of ichthyosaur varied in size, averaging 2-4 meters in length, though some fossils have been found at 15 meters long! By the Late Jurassic, around 100 million years after they appeared, the ichthyosaurs had established a shape which resembled modern-day porpoises.

Deadly Predator of the Sea

Like our dolphins and whales of today ichthyosaurs were air-breathing marine reptiles and they gave birth to live young in the sea. The later ichthyosaurs which resembled dolphins had four paddle-like fins, a shark-type dorsal fin and a fish-like tail. They had long, slender jaws with many sharp teeth, and large eyes which were strengthened by rings of bone. With these features the ichthyosaur became a fast swimmer and a good hunter, making it a deadly predator of the pre-historic seas.

Ichthyosaurs were carnivores and fed on various marine creatures. Some ichthyosaur fossils have been found with their stomach contents fossilised between their ribs, showing they mainly fed on fish and cephalopods such as squids and belemnites, using their teeth to crush the shells of their prey. This fossil in our collection contains tiny hooklets thought to be from belemnites which the ichthyosaur had eaten. View all the fossils in our collection

Ichthyosaurs in Yorkshire

Ichthyosaurs lived all over the World throughout their time in the Earth's seas. Their fossils have been discovered in many locations in Europe, North America and South America, spanning most of the Mesozoic Era. In the Lower Jurassic Period the area that is now East Yorkshire was covered by a warm sea where ichthyosaurs and other marine reptiles would have swam through the waters feeding on the rich supply of sea-life. This is why their fossils can be found in the rocks of this area, and many specimens in our collection were discovered around the Whitby area.

Ichthyosaurs decreased in species diversity during the Cretaceous Period, and finally became extinct in the Mid-Cretaceous. They were unable to compete with other marine reptiles which had adapted better to the conditions of the oceans. They were finally replaced as the top marine predator by the plesiosaurs, ending their reign of the seas almost 150 million years after they appeared on Earth.

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