They weren't dinosaurs
My wee boy loves dinosaurs (which means so does his little sister, as she really looks up to him and copies whatever he does and likes whatever he likes), so I went looking for a poster on dinosaurs for him (them). Searching through the poster rack at a local bookstore, I came across a decent-looking one - except, no it wasn’t. Sigh...
Across the top, in big bold lettering: Dinosaurs!
The first dinosaur listed? Pterodactyl.
Needless to say, I couldn’t buy that poster. I knew it was wrong, but surely I could overlook it just this once, seeing as it was for my four-year-old? Nope, because my four-year-old would spot the mistake as well!!! Yep, he already knows pterodactyls weren’t dinosaurs.
Wait, what??? You mean the flying dinosaur wasn’t a dinosaur???
That’s exactly what I mean. When I grew up my favourite dinosaurs were T-Rex, brontosaurus, pterodactyl, and dimetrodon. What do I have left now? T-Rex. Just one out of four. Because brontosaurus was never actually a thing (I’ve written a post about that). And pterodactyls weren’t dinosaurs. And it turns out, neither was dimetrodon. Sigh…
Oh and one other thing - there’s no such thing as a pterodactyl!!!
Most people think the four listed “dinosaurs” are just that, dinosaurs. Not everyone has a dad to explain what they actually were. I sure didn’t. And I’m not being sexist - it’s just that dads tend to be more into dinosaurs than mums do. Anyhoo, let’s pull apart the misconception.
The term dinosaur has unfortunately become for many people a catch-all term for anything reptilian and prehistoric. Which of course is not correct. The word is formed from two Greek words: deinos (which means terrible, powerful or wondrous) and sauros (which means lizard). Dinosaurs (animals belonging to the superorder Dinosauria) were a very diverse group of terrestrial (land-dwelling) reptiles that had a unique group of anatomical features. 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.
So now to clear up the misconception. Firstly, dinosaurs were land dwellers. So that rules out pterodactyls, who were flying reptiles. Except that they weren’t, as they never existed. No, the correct term is pterosaur. There were plenty of them (literally hundreds of genera), the most popular being pterodactylus and pteranodon. Unfortunately the term pterodactyl has stuck as a catch-all for ancient flying reptiles, even though it was never a thing. Now that we all know better, let’s correctly call them pterosaurs. But not dinosaurs.
Secondly, dinosaurs are defined in large part by the structure of their hips, which allowed them to walk with their legs directly beneath their bodies. And that rules out dimetrodon, which walked on four legs that sprawled out to the sides like modern lizards and crocodiles. Dimetrodon was actually a pelycosaur. They are usually described as being mammal-like reptiles, probably because pelycosaurs led to mammals, however the term mammal-like reptile is a misnomer as they weren’t actually reptiles. They were synapsids, a diverse group of animals which includes all modern mammals and ancient relatives from which mammals diverged. One other thing - dimetrodon lived from 280-245 Ma (mega-annum, basically millions of years ago), whilst dinosaurs lived 230-65 Ma. There wasn’t even any overlap. Dimetrodon was extinct well before the first dinosaurs evolved.
Oh and just to throw another spanner in the works, marine reptiles such as the ichthyosaurs and plesiosaurs? Also not dinosaurs.
Birds, on the other hand, are often referred to as living dinosaurs because they are descended from one of the five groups of dinosaurs, the theropods (the other groups are sauropods, thyreophorans, ceratopsians, and ornithopods).