While the era of dinosaurs is now fairly fixed in the popular consciousness, far less attention is given to the reptiles of the same time period that returned to the sea. While not dinosaurs, these reptiles too reached impressive proportions- and gained traits, like live birth and warm-bloodedness, that we now associate with mammals.

Take my hand and I’ll walk you through the world of seafaring reptiles, all the way back to diminutive Mesosaurus 300 million years ago…



“Atopodentatus unicus” is the freakiest tetrapod I have ever known; a marine reptile with hoof-like claws, a curved upper filled with hundreds of needle-like teeth, and a cleft that splits the upper jaw in two that has teeth inside it like some kind of Lovecraftian, eldritch abomination of evolution.

And I freaking love it.

Check it out.

Who’s that playing in the surf? It’s Atopodentatus unicus!

I’ve drawn this one before, way back during Marine Reptile Month, but since it recently got a facelift I think now’s a good time to revisit it.

Living during the Middle Triassic of southwestern China (~247-242 mya), Atopodentatus was a semi-aquatic marine reptile measuring about 3m long (9′10″). It was probably a member of the sauropterygians, related to placodonts and plesiosaurs, with its closest modern living relatives being turtles.

When first described in 2014 it was interpreted as having bizarre split jaws with a zipper-like appearance, but new discoveries of less crushed skulls have now given us a much better idea of how it looked.

And it’s still weird.

Its jaws were actually shaped like a broad “hammerhead” lined with many small teeth, which seem to be adaptations for rooting around on the seafloor in search of algae – making it the earliest known example of a herbivorous marine reptile. Imagine a mixture of a marine iguana, Nigersaurus, and a vacuum cleaner, and you’ve probably got a decent idea of what this creature was like.

The Evolution of Marine Reptiles

The various families of marine reptiles that ruled the seas during the dinosaur ages - icthyoaurs, plesiosaurs, mosasaurs and more - are as iconic of the Mesozoic as non-dinosaurs can get.  They’re equally as famous as the pterosaurs, and equally as misunderstood.  In this, the first of two posts acting as a quick and easy guide to marine reptiles, I hope the shed some light on how these diverse groups of creatures evolved.

Warning: This post is big as hell.

Keep reading