Ammonite A Cretaceous cousin of the modern octopus and squid. Ammonites protected their soft bodies inside hard, coiled shells. They snared their tiny prey with their long tentacles. They were a favourite food of marine reptiles such as the ichthyosaurs.

Champsosaurus A 2-metre-long (6.7-foot), crocodile-like marine reptile from the Cretaceous Period. Like modern crocodiles, it had a long snout lined with sharp teeth, four short legs and a long tail.

Elasmosaurus A large plesiosaur from the Late Cretaceous. Its long, snaky neck measured about 8 metres (26 feet) and was nearly half of its body length. Elasmosaurus may have used its long neck to catch fish by surprise. It could catch the fastest fish of its time.

Ichthyosaurs A group of marine reptiles with a body shape similar to that of modern dolphins. The name ichthyosaur means “fish lizard”. The ichthyosaurs lived from the Triassic to Mid-Cretaceous periods. They varied greatly in size: Mixosaurus was only 1 metre (39 inches) long, Ichthyosaurus was about 2 metres (6.6 feet) long, while Shonisaurus grew to more than 21 metres (70 feet). They all had large eyes, smooth, streamlined bodies and sharp, closely-set teeth.

Kronosaurus A 10-metre-long (33-foot) pliosaur from the Cretaceous. It had a huge head, about a quarter of its whole body length, and a short neck. Kronosaurus preyed on turtles, plesiosaurs, elasmosaurs, fish and squid.

Liopleurodon The largest of the pliosaurs. At 10 metres (33 feet) long, it was one of the biggest predators in the Jurassic seas.

Marine reptiles A group of now extinct aquatic animals that first emerged in the Triassic Period. They included the nothosaurs, placodonts, ichthyosaurs, plesiosaurs, pliosaurs and mosasaurs. They had scaly skin, sharp teeth, four flippers and a tail. Most were fierce hunters, chasing prey, such as fish, squid and shellfish. Like the dinosaurs, the sea reptiles breathed air, which meant that they regularly had to come to the water’s surface.

Mosasaurs A family of giant sea lizards from the Cretaceous Period. Some mosasaurs could grow up to 15 metres (about 50 feet) long. They had huge teeth and long, strong jaws. They probably preyed on fish and other marine reptiles, though some species may have eaten shellfish. Members of the family include Platecarpus, Tylosaurus and Mosasaurus.

Nothosaurs A group of Triassic marine reptiles with long necks and tails. Nothosaurs ranged in size from 60 centimetres to 4 metres (2–13 feet) long. They had legs and claws adapted for living on land as well as flippers suited for swimming, so they lived both on land and in the sea. Like modern seals, nothosaurs probably dived to catch fish, then dragged themselves on to the shore to rest. Members of this group include Nothosaurus, Lariosaurus, Ceresiosaurus and Pistosaurus.

Placodonts A group of small, armoured marine reptiles from the Triassic Period. Members of this family include Placodus, a 2-metre-long (6.7-foot) reptile, with a short neck and long legs, and Henodus, a bony-plated reptile, quite similar to modern turtles.

Plesiosauroids A group of large marine reptiles with four long, paddle-like flippers. Plesiosauroids were divided into two groups: the long-necked plesiosaurs and the short-necked pliosaurs.

Plesiosaurs A group of plesiosauroids with long, snake-like necks, small heads and four large flippers. They roamed the seas from the Triassic to the Cretaceous. Plesiosaurs included Plesiosaurus and Elasmosaurus.

Pliosaurs A group of plesiosauroids with short necks and huge, powerful jaws. They were the top predators of the Jurassic seas and fed on anything from small fish to other marine reptiles. Members of the group included Kronosaurus and Liopleurodon.

Teleosaurus A crocodile-like reptile from the Middle Cretaceous. It had a long slim body but, unlike modern crocodiles, it probably lived in the open ocean.

Consultant: Chris Jarvis