What is an ichthyosaur?

 

Ichthyosaur skeleton in a German museum

An ichthyosaur skeleton in a German museum

An ichthyosaur looks like a fish or maybe a dolphin, but it was actually a reptile. It lived in the Mesozoic seas while dinosaurs were walking on the land. They are not dinosaurs but they are so unlike any other reptile that palaeontologists aren’t sure what they are closely related to.

Ichthyosaurs went extinct about 90 million years ago so, unlike pterosaurs or non-bird dinosaurs, they didn’t become extinct because of a large meteor. Instead, palaeontologists think they wentextinct because newly evolved species of fish were faster and harder to catch. Other marine reptiles were more adaptable and replaced them in the late Mesozoic seas before the meteor hit.

Ichthyosaurs had fins instead of legs that they used for swimming. On their back they had a dorsal fin like those on many fish, and their tails also had a large crescent (moon-shaped) fin. They lived in the sea and were incapable of returning to land.

Most reptiles lay eggs but eggs are permeable to water. This means that if an egg falls in water then the infant inside would drown. But ichthyosaurs lived in water and couldn’t get onto land so ichthyosaurs gave birth to live young, as mammals do. Some fossil ichthyosaurs have even been found with babies half way out of the body. Palaeontologists think these ichtyosaurs died while giving birth.

Ichthyosaurs could be really large. The largest so far found is about 23m long. They also had massive eyes. One species called Opthalmosaurus has the largest eyes for its body size of any animal that has ever existed.

Here is a video of an ichthyosaur from the BBC’s Walking with Dinosaurs series:

What is a pterosaur?

A Pterosaur skeleton (David Peters, Wikimedia)

A Pterosaur skeleton (David Peters, Wikimedia)

While the dinosaurs ruled the land, the pterosaurs ruled the sky. Pterosaurs are flying reptiles that lived alongside dinosaurs during the Mesozoic period. They include the largest animals ever to fly, with some in the group being as large as a jet fighter and as tall as a giraffe.

Pterosaurs didn’t have feathers like birds but instead had a wing made of a membrane of thin skin. The wing was attached to the body and the arms and looks similar to a bat’s wing. But unlike a bats wing, a pterosaurs wing was supported by one very long finger that could be metres long (the finger is the same as our pinky finger).

Pterosaurs became extinct at the end of the Mesozoic period, 65 million years ago which freed the skies for bats and birds today.

Here is a video from the BBC’s Walking with Dinosaurs series:

What is a pliosaur?

The skull of a pliosaur (Greg Goebel, Wikimedia)

The skull of a pliosaur (Greg Goebel, Wikimedia)

Pliosaurs were big and vicious looking predators. They lived in the Mesozoic seas, and likely hunted almost anything that swam. They went extinct at the end of the Mesozoic.

Pliosaurs had very large fins instead of legs and had massive heads with rows of sharp teeth. They are quite rare fossils, and it’s usually only their skulls that are found.

One of the largest pliosaurs was found in England in Dorset. Only the skull was found, but it measured 2.4m long and palaeontologists estimate that the whole animal was about 15m. Click here for the BBC article on the find.

Here is a video from the BBC’s Planet Dinosaur about predator x, found in Dorset.

What is a plesiosaur?

Skeleton of a plesiosaur (Ballista, Wikimedia)

Skeleton of a plesiosaur (Ballista, Wikimedia)

Plesiosaurs are much like the sauropod dinosaurs in that they have an extremely long neck. They lived in the Mesozoic seas alongside ichthyosaurs and pliosaur, and went extinct at the end of the Mesozoic, 65 million years ago.

Plesiosaurs are very closely related to pliosaurs. Like pliosaurs, they had four very large fins that were used for swimming. Plesiosaurs also had very long necks and tails.

The first plesiosaur to be named and described was Plesiosaurus back in 1821. It came from the south coast of England, near Lyme Regis in Dorset. It was found by Mary Anning, one of the world’s first professional fossil collectors.

What is a dinosaur?

A triceratops in a museum (wikimedia)

A triceratops in a museum (wikimedia)

The name “dinosaur” means “terrible Lizard”. Englishman, Richard Owen was the man who created the name way back in 1842. The dinosaurs or Richard Owen’s world are much different from the ones we know now (look at picture below).

Two different models of Iguanodon. Top left is a modern reconstruction and bottom right is an 1854 reconstruction at Crystal Palace, London. (wikimedia sourced pictures, top: Marcus Ringer, bottom: FunkMunk)

Two different models of Iguanodon. Top left is a modern reconstruction and bottom right is an 1854 reconstruction at Crystal Palace, London. (wikimedia sourced pictures, top: Marcus Ringer, bottom: FunkMunk)

Dinosaurs were once thought of as slow cumbersome reptiles much like the komodo dragon. In the last few decades, palaeontologists have started to realise that dinosaurs were more complicated and more diverse than Owen could ever had imagined.

They lived from 248 to 65 million years ago, although most palaeontologists now believe birds are in fact modern dinosaurs. They could be huge with long necks and small heads or tiny with large brains and killer claws and teeth.

What makes a dinosaur a dinosaur?
Dinosaurs looked and act very differently to each other. Some were massive, and were over 30m long while others were the size of a chicken. Some ate meat, others ate fish and lots ate plants. Some dinosaurs walked on two legs and others walked on four. Some had very long necks while others had large horns. Some had powerful arms and claws while others had tiny arms and massive heads packed with large, sharp teeth.

But there are some things all dinosaurs had in common. Dinosaurs have an erect posture which means that their legs were straight and under the body, much like us. Most reptiles have sprawling legs, their legs come out from their sides and away from the body like any lizard or crocodile.

The two postures of reptiles.  left: sprawling posture of lizards and crocodiles. Right: erect posture of dinosaurs and mammals.

The two postures of reptiles. left: sprawling posture of lizards and crocodiles. Right: erect posture of dinosaurs and mammals.

Many animals lay eggs but dinosaurs laid eggs similar to birds and crocodiles. Their eggs are hard shelled. Other reptiles like snakes and lizards have soft shelled eggs as do fish and amphibians (and even a couple of mammals). The hard shells means that palaeontologists find the fossil remains of eggs which sometimes have baby dinosaurs still inside.

Birds are dinosaurs
Fossils show that dinosaurs had feathers like many birds and many of the first birds had teeth and clawed hands like in the famous Archaeopteryx. All the similarities between birds and dinosaurs mean that most palaeontologists now believe that birds are just modern dinosaurs.

There are over 9,000 species of birds alive today which is much more than the 5,000 mammals so maybe we are still in the age of dinosaurs after all.