Why aren't pterosaurs dinosaurs?

01 March, 2009

An artist's reconstruction of Pteranodon, one of the better known Pterosaurs.
An artist's reconstruction of Pteranodon, one of the better known Pterosaurs.
Image: Kate Nolan (illustrator)
Source: Museum Victoria

Question: I have been keeping up with your fascinating blog about the development of your new science exhibitions. I just read the article about the giant Pterosaur and learned that Pterosaurs are not dinosaurs. Can you tell me why not? What exactly is a dinosaur?

Answer: The word “dinosaur” is formed from two Greek words: deinos (which means terrible, powerful or wondrous) and sauros (which means lizard). The term “dinosaur” is commonly used to describe all species of prehistoric reptile, but not all prehistoric reptiles are true dinosaurs.

Dinosaurs (animals belonging to the superorder Dinosauria) were a very diverse group of terrestrial (ground-dwelling) reptiles that had a unique group of anatomical features. Pterosaurs are flying reptiles and are therefore excluded from this definition. Aquatic reptiles, such as the ichthyosaurs, plesiosaurs, and mosasaurs, are also not dinosaurs.

One of the main features that distinguished dinosaurs from other reptiles was the structure of their limbs, which were held directly beneath their body. This gave them an erect posture. Prehistoric lizards and crocodiles are therefore not dinosaurs – their limbs stick out from their bodies, giving them a sprawling gait.

True dinosaurs include:

  • Theropods: these include the large carnivorous dinosaurs that stand on their hind legs, such as Tyrannosaurus.
  • Sauropods: these include the large herbivorous dinosaurs that mostly stand on all fours, such as Diplodocus.
  • Thyreopherans: the armored herbivorous dinosaurs that stand on all fours,  such as Stegosaurus.
  • Ceratopsians: the herbivorous dinosaurs that stand on all fours and have horns and frills, such as Triceratops.
  • Ornithopods: the herbivores dinosaurs with bird-like hips and feet (most have three toes) and duck-like bills, such as Hadrosaurus.

Birds are often referred to as “living dinosaurs” because they are descended from one group of dinosaurs – the theropods. Birds are, in fact, the only living descendants of the dinosaurs.

Dinosaur Walk, a new permanent exhibition, will open at Melbourne Museum in April 2009. This exhibition will feature dinosaurs, flying reptiles and megafauna. Current visitors to Melbourne Museum are able to watch the development of this exhibition from the upper level and through viewing windows on the ground level.

Quetzalcoatlus (the world’s largest flying reptile) and two other pterosaurs are already in position – soaring over the Dinosaur Walk construction zone – keeping watch as the other enormous skeletons are installed beneath them.

Comments (2)

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Rich Harrison 14 July, 2013 11:28
I thought the Tuatara of coastal islands in New Zealand were considered relatives of the dinosaurs as well as the modern day birds... is this so?
Discovery Centre 19 July, 2013 13:38
Hello Rich - The relationship of theTuatara to dinosaurs if often misquoted. Tuatara are the only living representatives of a group of reptiles called Rhynchocephalians that arose before the dinosaurs, and the lineage that gave rise to 'modern' reptile groups. Whilst they are from a group of reptiles that pre-date the evolution of crocodiles, dinosaurs and birds, Tuatara are not as closely related to dinosaurs as birds are.
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