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.

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