Random Reptile Generator

What the random reptile generator does

You need a reptile. A creature for a game, a subject for a report, an animal for a child who has just discovered that some animals are better than others and would like to know about the good ones.

Press the button and you get one.

What follows is a chain of four increasingly annoying facts, and by the end of them the word in the heading above will have fallen apart in your hands. Fair warning.

How to use it

1. Choose how many you want. One if you are deciding, more if you are browsing.
2. Press Generate. A fresh draw every time.
3. Press Copy to take the set with you.

The one in here that is not a lizard

Somewhere in this list is an animal called a tuatara.

It lives on a few islands off New Zealand. It is about the size of a forearm, it is greenish brown, it has a spiny crest down its back, small clawed feet, a pointed tail, and a general air of having been assembled from a lizard kit. Put a photograph of one in front of anybody on Earth and they will say lizard.

It is not a lizard.

Not "technically not a lizard" in the way that a peanut is technically not a nut. Not a lizard in a way that is difficult to overstate. The tuatara's ancestors and the ancestors of every lizard alive today went their separate ways about 250 million years ago, in the Triassic, before there were dinosaurs worth mentioning and long before there was anything you would call a mammal.

Here is the comparison that makes it land. You are more closely related to a kangaroo than a tuatara is to a lizard.

Sit with that. A kangaroo. Everything you and a kangaroo have in common, warm blood, milk, hair, the same basic skeleton, a placenta of sorts, and you two split more recently than a tuatara and a gecko did. The gecko and the tuatara look like cousins and are barely acquainted.

It fooled the professionals too. When a skull reached the British Museum in 1831 they filed it as a lizard and it sat there being a lizard for thirty-six years, until Albert Günther looked at it properly in 1867 and noticed it had features pointing at birds and turtles and crocodiles rather than at lizards at all. He proposed an entirely new order for it. He called it Rhynchocephalia, which means beak head.

The tuatara is the only one left in it.

That order was not always a party of one. Rhynchocephalians were everywhere in the Mesozoic, common and varied and spread across the world. Then the range began shrinking from the Early Jurassic onward, and it kept shrinking, and the last one anybody has found outside New Zealand is a fossil from Argentina from around seventy million years ago. Everything else in the order died. One species did not, on some islands, at the bottom of the world.

When its genome was finally sequenced in 2020 it came in at around five gigabases, among the largest of any vertebrate anyone has assembled, and the analysis confirmed the split at roughly a quarter of a billion years. It also turned out to be the slowest-evolving animal of its wider group yet measured, which is a strange and slightly haunting result for the last member of anything.

And then it turns out lizards are not a thing either

Fine, you think. The tuatara is a weird exception. The rest of the list is normal. There are lizards, and there are snakes, and there are turtles, and there are crocodiles.

Snakes are lizards.

Not similar to lizards. Not descended from something lizard-ish. Snakes sit inside the lizard family tree. Somewhere in the middle of the lizards, a branch lost its legs, and everything on that branch is what we call snakes, and the branches on either side of it are still called lizards.

Which does something uncomfortable to the word. If you draw a circle around all the lizards and you have left the snakes out, you have not drawn a circle around a real group. You have drawn a circle around some of a real group and quietly excluded a bit you find visually distinctive. The proper group, the one that includes the whole branch, is called Squamata, and it holds the lizards and the snakes and the strange burrowing amphisbaenians together, because they are together whether anybody likes it or not.

So the king cobra and the green iguana in this list are not two kinds of animal. They are one kind of animal, and one of them has misplaced its legs.

The crocodile is closer to a sparrow than to the Komodo dragon

Now the one that breaks people.

There is a Nile crocodile in this list. There is a Komodo dragon in it too. They are both large, both scaly, both alarming, both would ruin your afternoon. Anybody would file them next to each other.

The crocodile is not closely related to the Komodo dragon. The crocodile is closely related to birds.

Crocodiles belong to a group called the archosaurs. So did the dinosaurs. And the birds are dinosaurs, not descendants of dinosaurs in a poetic sense but actual surviving members of the group, which means the crocodile and the sparrow on your windowsill are on the same branch, and the Komodo dragon is off on the squamate branch with the snakes and the geckos, a very long way away.

The crocodile has more in common, by ancestry, with a chicken than with any lizard alive.

And once you know it you can see it. Crocodiles build nests and guard them. They care for their young. They vocalise, and the babies call from inside the egg so the mother knows to dig them out. They have a four-chambered heart, which lizards do not. None of that is crocodiles being unusually bird-like. That is a family resemblance.

What is actually in the word

So gather it up. Everything in this list, plus every bird alive, forms one real group with one common ancestor. That group is genuine and has a shape and you could draw it.

Now take the birds out.

What is left is what the word "reptile" means. Not a family. A remainder. It is the animals that were in the group before somebody removed the ones with feathers, which they did because feathers are noticeable and because birds are charismatic enough to have been given their own department long before anybody worked out where they had come from.

This is the only major group of animals we routinely name by exclusion. Nobody defines mammals as everything furry except humans. But that is exactly the shape of "reptile", and it is why the word keeps generating these little shocks: it is not describing a branch of the tree, it is describing a branch with a piece torn off, and the torn edge keeps showing.

Which brings it back round to the tuatara, sitting on an island, being the last of an order that stopped mattering seventy million years ago, in a category that does not entirely exist, still being mistaken for a lizard by everyone who sees it.

It has a third eye, incidentally. An actual light-sensing patch on the top of its skull, visible on hatchlings before the scales grow over it. Almost nobody knows that, and it has been up there the whole time.

Where these come from

The animals are drawn from a list our team researched and checked by hand, so the names are real species rather than approximations. Your browser picks from them at random. Nothing you do here leaves your device.

Questions people ask

So are birds reptiles or not?

By ancestry, yes, unavoidably. In ordinary speech, no, and nobody is going to change that, nor should they. Both statements are useful and they are answering different questions. A biologist tracing descent has to include birds. A person pointing at a hedge does not.

Were dinosaurs reptiles?

They were archosaurs, on the same branch as crocodiles, and birds are the ones that made it through. So the answer runs into exactly the same problem as the question above, and for the same reason. Dinosaurs did not go extinct so much as go quiet and get smaller and start eating from your table.

Where do turtles fit?

Turtles were an argument for a very long time, because their skulls are unusual enough to hide the evidence. The current answer from genetics puts them out near the archosaurs, which is to say nearer to the crocodiles and the birds than to the lizards. Not what anybody expected from looking at them.

Can I see a tuatara?

Yes, in New Zealand, in several sanctuaries and zoos that run breeding programmes. They are a taonga, a treasure, to Māori, and the research done on them, including the genome work, was done in partnership with iwi rather than around them. They can live for something like a century, so a tuatara sitting still and ignoring you may well outlast you.

Are reptiles cold-blooded?

The phrase is doing more harm than good. Their blood is not cold, it is whatever the day is. They regulate temperature by moving, which is why a lizard on a rock is not resting but working. Some manage it well enough to keep a surprisingly steady body temperature all day, using nothing but the sun and good judgement about where to stand.

Can the same animal come up twice?

Not within a single draw. Ask for ten and you get ten different ones. Press again and everything is back in play.

References

1. Gemmell, N. J. et al. (2020). The tuatara genome reveals ancient features of amniote evolution. Nature, 584, 403 to 409. https://doi.org/10.1038/s41586-020-2561-9
2. Hoffbeck, C. et al. (2024). Gut microbiome of the sole surviving member of reptile order Rhynchocephalia. Ecology and Evolution, 14(2). https://doi.org/10.1002/ece3.11073
3. An Ancient Reptile in Peril: The Curious Genome of the Tuatara. EMBL-EBI. https://scitechdaily.com/an-ancient-reptile-in-peril-the-curious-genome-of-the-tuatara-a-vulnerable-species-that-is-not-a-lizard/
4. Meet the Tuatara: New Zealand's Bizarre Ancient Reptile. The Nature Conservancy. https://blog.nature.org/2025/07/20/meet-the-tuatara-new-zealands-bizarre-ancient-reptile/