A fossil of an ichthyosaur

Object info
Ichthyosaur fossil, Jurassic period

Where to see it
Hull and East Riding Museum of Archaeology

Accession number

Purchase a print or image licence
Ichthyosaur Fossil on Bridgeman Images

About the object

This is the fossil of an ichthyosaur – an extinct marine mammal that once swam in seas all over the world. Based on fossil evidence, ichthyosaurs first appeared on our planet 250 million years ago. They disappeared around 95 million years ago.

The word ichthyosaur comes from the Greek words "ichthyos" meaning fish, and "sauros" meaning lizards or reptiles. Because of that, ichthyosaurs are also known as fish-lizards! 

About ichthyosaurs

Ichthyosaurs were most abundant in the Late Triassic and Early Jurassic Periods. In other words, they were swimming through the oceans while dinosaurs roamed the land.

Many different species of ichthyosaur existed during their time on Earth. The earliest ichthyosaurs were long and eel-like. But as the group evolved, their body shape became more fish-like. The different species of ichthyosaur also varied in size, averaging 2–4 m in length (though some fossils have been found at 15 m long!). 

By the Late Jurassic Period (around 100 million years after they first appeared), the ichthyosaur's shape resembled a modern-day porpoise. And, like today's dolphins and whales, they were air-breathing marine reptiles that gave birth to live young in the sea. 

Deadly Predator of the Sea

The later ichthyosaurs had four paddle-like fins, a shark-type dorsal fin and a fish-like tail. They also had long, slender jaws with many sharp teeth and large eyes strengthened by rings of bone. Thanks to these features, ichthyosaurs became fast swimmers and good hunters. A deadly predator of prehistoric seas.

Ichthyosaurs were carnivores and fed on various marine creatures. Some ichthyosaur fossils have their stomach contents fossilised between their ribs. This shows us they mainly fed on fish and cephalopods (such as squids and belemnites). They will have used their teeth to crush the shells of their prey. The fossil in our collection contains tiny hooklets thought to be from belemnites the ichthyosaur had eaten. 

Ichthyosaurs in Yorkshire

Ichthyosaurs lived all over the world. People have discovered their fossils in Europe, North America and South America, spanning most of the Mesozoic Era. 

In the Lower Jurassic Period, a warm sea covered the area that's now East Yorkshire. There, ichthyosaurs and other marine reptiles would have thrived. We know this because their fossil remains are found in rocks from this area. Many specimens in our collection were discovered around Whitby.

The end of the ichthyosaurs

Ichthyosaurs decreased in species diversity during the Cretaceous Period. They couldn't compete with other marine reptiles that had adapted better to the conditions of the oceans. 

Ichthyosaurs finally became extinct in the Mid-Cretaceous, replaced by plesiosaurs as the top marine predator. Thus their reign of the seas ended after almost 150 million years on Earth.