Welcome to the Cretaceous period, which existed between 65 and 144 million years ago!   More varieties of animals and plants lived than ever before – from the dinosaurs on the land to the plants they ate.  Things were getting pretty busy underwater too!

Dinosaurs didn’t go into the oceans but that didn’t mean they were empty.  Far from it – much of the sea life from the Jurassic period remained, including Ichthyosaurs – agile dolphin-like creatures, as well as starfish and ammonites – soft shellfish with long streaming tentacles.

Some Cretaceous ammonites were enormous – as much as two metres in diameter, and much bigger than their Jurassic relatives.

Along with these older creatures, new types of fish were appearing – the ancestors of those we find in our seas today.  These included “rays” – flat fish with wing-like fins – and “teleosts” – bony fish, not so different to the cod you get in the chip shop.

The wide variety of life made the oceans an attractive place for predators.  Sharks, like those seen today, battled alongside much larger plesiosaurs – powerful reptiles with large flippers and a long neck.  But towards the end of the Cretaceous period, a terrifying predator ruled – the Mosasaur!

Mosasaurs looked like streamlined lizards – their short paddle-like limbs and powerful tails were ideal for fast swimming, enabling them to pounce underwater at prey.  Smaller specimens crunched on sea urchins and molluscs, whilst the largest varieties, some 17 metres long, preyed on birds, fish and reptiles, and even other Mosasaurs!

Mosasaurs had a double-hinged jaw and flexible skull (much like a snake) which meant they could almost gulp down their prey whole – again, just like snakes or Komodo dragons.

How do we know what the world looked like millions of years ago?

Scientists piece together evidence from fossils using lots of different techniques, including microscopes, to look at tiny details, and CT scanners to peer inside.  They record information about where a fossil was found, examine its surroundings, look at what animals ate and compare fossils to similar animals alive today – like comparing the Mosasaurs to snakes.

Computers are used to take this data and create models – from simple black and white pictures to exciting moving animated monsters.

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