When most people picture dinosaurs, they’re thinking of massive creatures that dominated prehistoric Earth for millions of years.
However, loads of the animals we casually call dinosaurs weren’t actually dinosaurs at all. They lived alongside them, they died out around the same time, and they’re in all the dinosaur books, but technically, they belong to completely different groups. The confusion’s so widespread that even museum exhibits sometimes lump them all together. Here are the prehistoric creatures that fooled everyone into thinking they were dinosaurs when they were something else entirely.
1. Pterodactyls and all flying reptiles
Pterodactyls are probably the most famous not-actually-dinosaurs. They’re flying reptiles called pterosaurs, which is a completely separate group. People see them in dinosaur films and books and just assume they’re flying dinosaurs.
Dinosaurs are defined by specific hip structures and leg positions. Pterosaurs had wings made of skin stretched between an elongated finger and their body. They’re relatives of dinosaurs, but they’re not dinosaurs themselves, just like bats aren’t birds even though they fly.
2. Plesiosaurs with the long necks
Those long-necked marine reptiles that people picture in the ocean alongside dinosaurs weren’t dinosaurs, either. Plesiosaurs were marine reptiles that evolved completely separately. The famous Loch Ness Monster is supposedly a plesiosaur, if it existed.
Plesiosaurs had flippers and lived entirely in water. Dinosaurs were land animals with legs positioned directly under their bodies. The two groups are only distantly related, despite living during the same time periods and both being reptiles.
3. Mosasaurs and other sea monsters
Mosasaurs were massive marine predators that could grow over 15 metres long. They’re in every prehistoric ocean documentary, but they weren’t dinosaurs. They were actually more closely related to modern monitor lizards and snakes.
These creatures ruled the seas, while dinosaurs ruled the land. They had paddle-like limbs and gave birth to live young. Dinosaurs laid eggs and weren’t adapted for ocean life. Mosasaurs are marine reptiles, not dinosaurs.
4. Ichthyosaurs that looked like dolphins
Ichthyosaurs looked remarkably like dolphins, but they lived during the age of dinosaurs. They’re often shown swimming in prehistoric seas in dinosaur books. Despite this, they’re not dinosaurs at all.
These were marine reptiles that evolved to look like fish through convergent evolution. They had fins, streamlined bodies, and some even had dorsal fins. But they’re no more dinosaurs than actual dolphins are, they just happened to exist at the same time.
5. Dimetrodon with the big sail on its back
Dimetrodon shows up in loads of dinosaur toy sets and books. That distinctive sail on its back makes it look properly prehistoric. But it wasn’t a dinosaur, and it wasn’t even alive during the dinosaur era.
Dimetrodon lived about 40 million years before the first dinosaurs even evolved. It was a synapsid, which means it’s actually more closely related to mammals than to dinosaurs. It’s closer to you than it is to a T. rex, which is mental when you think about it.
6. Pteranodons from Jurassic Park
Pteranodon is another flying reptile that gets lumped in with dinosaurs constantly. It’s in the Jurassic Park films and appears in nearly every dinosaur exhibition. Still not a dinosaur, though.
Like all pterosaurs, Pteranodon was a flying reptile but from a different evolutionary branch. The name literally means “winged and toothless”. It soared over oceans eating fish while dinosaurs were doing their thing on land. Related but separate groups entirely.
7. The massive Liopleurodon
Liopleurodon was an enormous marine predator that’s become famous through documentaries. People assume anything that big and prehistoric must be a dinosaur. It absolutely wasn’t.
This was another plesiosaur, a marine reptile with four flippers. It was an apex predator in Jurassic seas, but it’s not related to dinosaurs beyond being reptiles. Its skull alone could be two metres long, but being massive and ancient doesn’t make something a dinosaur.
8. Archelon, the giant turtle
Archelon was a turtle the size of a small car that lived during the Cretaceous period. It shows up in books about prehistoric life and people think of it as a dinosaur-era creature, so they assume it’s a type of dinosaur.
Turtles are reptiles, but they’re not dinosaurs. They evolved separately and have been around for even longer than dinosaurs existed. Archelon was just a really big turtle living at the same time as dinosaurs, nothing more than that.
9. Tanystropheus with the ridiculously long neck
Tanystropheus had a neck that was longer than its body and tail combined. It looks like something from a dinosaur nightmare, but it lived before dinosaurs existed and wasn’t one anyway.
This bizarre reptile was an archosaur, which is the broader group that includes dinosaurs, but it’s not a dinosaur itself. Think of it like how humans and lemurs are both primates, but humans aren’t lemurs. Tanystropheus was doing its weird long-neck thing before dinosaurs even showed up.
10. Nothosaurs and their seal-like lifestyle
Nothosaurs looked a bit like prehistoric seals, with webbed feet and streamlined bodies. They lived during the Triassic period alongside early dinosaurs, but they weren’t dinosaurs themselves.
These were sauropterygians, the group that would later evolve into plesiosaurs. They could move on land and in water, a bit like modern seals. But having flippers and living during the dinosaur era doesn’t make you a dinosaur, it just makes you a contemporary.
Why does everyone get this wrong?
The confusion happens because all these animals lived during the Mesozoic Era, the age of dinosaurs. They’re all extinct reptiles from roughly the same time period, so people lump them together. Museums and books about dinosaurs often include them because they’re explaining what prehistoric life was like.
But dinosaurs are a specific group defined by their anatomy. They had legs positioned directly under their bodies, specific hip structures, and holes in their skulls. They lived on land, walked on legs, and laid eggs. Anything that flew or lived in water wasn’t a dinosaur, no matter how prehistoric or reptilian it was.
So what actually counts as a dinosaur?
Real dinosaurs include T. rex, Triceratops, Stegosaurus, Brachiosaurus, Velociraptor, and all their relatives. They’re split into two groups based on hip structure. Birds are actually living dinosaurs, which is the only dinosaur lineage that survived the mass extinction.
Everything else that’s not a bird is either a different type of prehistoric reptile or something else entirely. The flying ones were pterosaurs. The swimming ones were various groups of marine reptiles. The really ancient ones before dinosaurs existed were different reptile groups entirely. They’re all fascinating, but they’re not dinosaurs, no matter how many times they appear in dinosaur books.