4 "Dinosaurs" that Weren't Dinosaurs

When you picture the prehistoric "monsters" who once dominated the planet, the word "dinosaur" is probably the first thing that comes to mind. You can probably think of at least a dozen species of dinosaur, from those you studied in kindergarten to the romping baby dinos in The Land Before Time.

Surprisingly, though, most of the pictures you imagine when you think "dinosaur" aren't dinosaurs at all. They are classified as non-dinosaur archosaurs, and they actually comprised the majority of prehistoric reptiles. Dinosaurs themselves only comprised a small fraction-- about ten percent-- of reptiles during the mesozoic era. The following most common "dinosaurs" weren't dinosaurs at all.

1. Plesiosaur

Plesiosaurs were massive aquatic reptiles, which lived in saltwater ecosystems. Some plesiosaurs superficially resembled land-dwelling sauropod dinosaurs, such as brachiosaurus and apatosaurus, but it was completely unrelated to sauropods. It was a carnivorous archosaur and was only distantly linked to any dinosaur species. Plesiosaurs actually had a classification all to themselves.

2. Ichthyosaur

Another marine reptile, the ichthyosaur or "fish lizard" was also a predator, and best known for its shark-like appearance. Ichythosaurs were also well-known "dinosuars" who weren't dinosaurs; they were independently classified. Ichthyosaurs have no living descendants today.

3. Pterosaurs

Pterosaurs, including the well-known pterodactyl, are the most popular of "flying dinosaurs." In reality, there were no flying reptilian dinosaurs whatsoever. No reptilian dinosaur species ever flew, and the pterosaurs were classified in a separate clade. Although they were related to true dinosaurs, they do not fit the genuine definition of a dinosaur.

4. Dimetodon

You may not know dimetodon by name, but you would probably recognize it for its sail-backed, lizard-like appearance. Dimetodon actually existed long before the dinosaurs and persisted long after them. Dimetodon skeletons dating back 245 years-- several million years before dinosaurs evolved. This archosaur also survived the extinction event that wiped out most dinosaurs, but its reputation as a prehistoric reptile has earned it an inaccurate name.

Although the taxonomical details are unimportant to giving us a vision of the ancient past, it is interesting to consider how pervasive myths are regarding what is and isn't a dinosaur. And chew on this-- while the pterodactyl is definitely not a dinosaur, all birds surviving today are, technically, species of dinosaur.

You can read more about "dinosaurs" who weren't dinosaurs at the Guardian.