Of the 700 or so dinosaur species paleontologists have discovered to date, some are terrifying, some are magnificent and others are downright bizarre. Those in the last category won’t haunt your nightmares like Spinosaurus or lend grandeur to a Jurassic Park scene like Brachiosaurus; mostly, they’ll just leave you wondering what Mother Nature was smoking in the Mesozoic Era (and where you can get some).

The Weirdest Dinosaurs

Here are a few of the preeminent weirdos:

1. Mononykus

When it comes to stunted limbs, T. rex gets all the attention. But the Mononykus, which looks a bit like an unadorned peacock, does the tyrant lizard one better: In place of each arm, it sported a single 3-inch claw.

The purpose of these diminutive hooks remains a mystery. Though they don’t seem well-suited for catching prey or digging burrows, some experts have proposed that Mononykus used them to extract insects from their nests, much like modern anteaters and pangolins. This would be, as Fayetteville State University paleontologist Philip Senter writes, “an unusual niche for a dinosaur.”

2. Deinocheirus

At the opposite end of the appendage spectrum is Deinocheirus, which aptly translates to “terrible hand.” For half a century, the world knew this species only by two 8-foot arms with massive claws excavated in 1965 in Mongolia. Then, in 2014, new specimens finally filled in the rest of the picture, an amalgam so strange it rivals the platypus.

Besides its blunt talons (perhaps used to dig up plants), this stout, lumbering beast had a duck’s bill, a camel’s hump, and possibly a set of fan-like tail feathers. University of Edinburgh paleontologist Stephen Brusatte once described it as “something out of a bad sci-fi movie.”

3. Kentrosaurus

Meet Stegosaurus on steroids. Kentrosaurus is, in fact, a close relative with many similar features: Two rows of armored plates lined its back, morphing gradually into sharper spikes and culminating in a pair of deadly spears at the tip of the tail.

Digital analysis of this creature’s body mechanics suggests that it could swing its “thagomizer” (the incredible technical term for a stegosaur’s spiked tail) in a 120-degree arc at a bone-breaking 20 miles per hour. As if that weren’t enough to keep predators at bay, two more outlandish spikes protruded from its shoulders.

4. Microraptor

At just 2.5 feet in length, this little fella crams a lot of peculiarity into a small package. Like a living biplane, Microraptor boasted two sets of wings — that’s four in total, one each on its hind and forelimbs. The Wright brothers would’ve been proud.

Just like the better-known Archaeopteryx, fossils of Microraptor offer a window into the early evolution of birds from dinosaurs. It’s unclear whether they actually flew — and if they did, whether they were capable of powered flight or simply drifted down from treetops using their limbs for lift. The second scenario could suggest that avian flight originated in abilities similar to those we see today in flying squirrels. (Someone ought to let them know — gliding is so 125 million years ago.)

5. Bajadasaurus

If this striking, elephant-sized herbivore is any indication, we’ve only begun to fathom the depths of dinosaur weirdness. First described in 2019, Bajadasaurus wore a mohawk better than any latter-day punk rocker. A row of spectacular elongated spines point forward from its neck, almost like an arched fence, perhaps for sexual display, passive defense or even thermoregulation. 

The bones themselves are improbably long, but they may have been just the foundation for a sheath that was 50 percent longer; since the bones are connected directly to the spinal cord, that extra impact protection would have been crucial. (It’s also possible the bones supported a sail, à la Dimetrodon, but isn’t it more fun to imagine a Cretaceous precursor to Travis Barker?)