This is NOT a dinosaur

dimetrodon skeleton

What is a dinosaur? And how can we distinguish other species from dinosaurs? We know from fossils that dinosaurs were around a long, long time ago, lived on land and were reptiles. There are many animals that lived a long time ago, some even before dinosaurs and some at the time that are not, in fact, dinosaurs themselves! Do you know how we can tell that they are NOT dinosaurs?

This one walks differently

This is NOT a dinosaur.

Actually, this is not even a bad model of a dinosaur. THIS is a dimetrodon. (OK, it’s a bad model of a dimetrodon).

Dimetrodons became extinct around 20-30 million years before dinosaurs started to evolve so they were already animals that lived a long, long time ago from the dinosaurs’ perspective! They were mammal-like reptiles.

You may be wondering how you could tell at first glance, if someone waved this model in your face, that it is not a dinosaur? Or, more importantly, how can you explain to a child that what looks like a dinosaur, was around a long, long time ago, lived on land and was a reptile is NOT A DINOSAUR? Just look at the legs or hip bones. If they stick out to the sides like a crocodile, then it’s not a dinosaur. Children can experience the difference this makes by doing push-ups – compare bending the arms to the side with bending them alongside your body. This is one of the reason why a Dimetrodon is NOT a dinosaur and why a crocodile is not a dinosaur.

This one flies

This is NOT a dinosaur.

This is a pterodactylus. These flying prehistoric reptiles were at least around at the same time as dinosaurs. However, they are also not dinosaurs.

Again, it comes down to the bone structure. The peterodactylus belongs to the pterosaurs, meaning wing lizard. Their hip bones distinguish them from dinosaurs. 

Does that mean that anything that flies is not a dinosaur? Unfortunately, it’s not that simple. There was a dinosaur called archaeopteryx (the name means old bird), much smaller than the large perosaurs, that could fly for short bursts. 

This one swims

Plesiosaurus

This is NOT a dinosaur.

I’m on safer ground now, or rather, I am not on ground at all. A dinosaur is a land animal so therefore a plesiosaurus is NOT a dinosaur. 

Again, it’s down to the bone but the quick answer is that a prehistoric, aquatic mammal is not a dinosaur.

This one is a mammal

This is NOT a dinosaur.

This is obviously not a reptile so it can’t be a dinosaur. This is a prehistoric land animal that does appear in the fossil record and should be mentioned. 

This is a diprotodon, which was part of Australia’s megafauna, giant land animals that lived millions of years after dinosaurs became extinct. Famous megafauna include mammoths and the ground sloth, a huge 20 foot sloth that live in South America. Some megafauna are still alive today, elephant and rhinoceros, for example. Extinct Australian megafauna included the wombat-like, marsupial diprotodon, the marsupial, lion-like thylacoleo and the reptile megalania, an extinct species of monitor lizard (still NOT a dinosaur).

So hopefully this has helped and not confused you further. Remember, not all fossil creatures are dinosaurs.

Hayley Bates
Article author: Hayley Bates
National Certifications Coordinator

This passionate mathematician and former science teacher will inspire you with her enthusiasm for inquiry-based learning and her determination to provide high-quality hands-on and fun professional development.

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