12 Scariest Dinosaurs You'd Want to Avoid While Time Traveling

Imagine a Velociraptor scaled up to nightmare proportions. Utahraptor measured nearly 20 ft (6 m) long and lived in the early Cretaceous. It had massive claws, serrated teeth, and may have hunted cooperatively to bring down large herbivores.

Spinosaurus didn’t just scare other dinosaurs; it probably scared anything it met. This huge predator lived during the Cretaceous period and was even larger than T. rex, reaching lengths over 50 ft (15 m).

With a crocodile-like skull, conical teeth for gripping fish, and a massive sail along its back, it was a semiaquatic predator that likely spent much of its life in the water.

Scientists believe its distinctive combination of adaptations made it one of the most versatile and dangerous animals of the Mesozoic era.

With claws stretching over 3.3 ft (1 m) long, Therizinosaurus looked like a nightmare, even though it was a herbivore.

Its sported a distinctive combination of long arms, sickle-like claws, and massive body size.

The most iconic of all, T. rex was the apex predator of the late Cretaceous period. Standing over 40 ft (12 m) long and weighing up to 10 tons (9 metric tonnes), it had the strongest bite force of any land animal ever studied.

Its serrated conical teeth could easily break bones, making it one of the most dangerous dinosaurs to ever roam Earth millions of years ago. Despite its short arms, T. rex was built for power and terror, much like the great white shark is in today’s oceans.

This distant cousin of T. rex lived in what is now South America during the late Cretaceous. Giganotosaurus grew up to 43 ft (13 m) long, making it one of the largest predators ever.

It had three-fingered hands, sharp claws, and serrated teeth that made it a nightmare for large prey. Though it may not have had the strongest bite force, its sheer size and hunting abilities put it among the scariest and deadliest dinosaurs.

With two horns above its eyes and a lightweight body, Carnotaurus was an ambush predator built for speed. It roamed South America during the late Cretaceous period and used its powerful jaws to take down prey, while its small arms were likely not used in hunting.

Its unusual skull shape and sharp teeth gave it a distinct look, making it a standout in the "Jurassic Park" franchise and a real-life terror.

Dominating the late Jurassic period, Allosaurus was one of the top large carnivores before T. rex came along. It measured up to 33 ft (10 m) long and used its massive claws and sharp teeth to take down prey like Stegosaurus.

Some experts have speculated Allosaurus might have hunted in packs, but this remains unproven.

Though only about the size of a turkey, Velociraptor earned its deadly reputation through cunning, speed, and sickle shaped claws. This Cretaceous predator likely did not hunt in groups and instead used ambush strategies to take down prey, including larger dinosaurs.

It’s a staple of the "Jurassic Park" franchise for good reason: Pound for pound, it was one of the most dangerous animals of its time.

Another group-hunting predator, Mapusaurus may have taken down the enormous Argentinosaurus, one of the largest land animals ever.

These predators likely used teamwork to hunt massive prey, suggesting that cooperative pack hunting allowed them to take down even gigantic prey.

Ankylosaurus may not have hunted other dinosaurs, but it could break them. This herbivore ankylosaurus lived during the late Cretaceous period and had a tail tipped with a massive bony club.

That weapon, combined with body armor, made it one of the most dangerous animals to predators like T. rex.

Though it wasn’t a predator, Stegosaurus had defenses that could stop one. Its spiked tail, called a thagomizer, could puncture or crush the bones of attackers.

Combined with its armored back, it was a formidable opponent for any meat-eater daring enough to try.

This three-horned herbivore wasn’t just for show. Triceratops lived in the late Cretaceous and used its horns and massive skull to fend off apex predators like T. rex.

Its sheer size and defensive tools made it one of the most dangerous dinosaurs to mess with, even if it didn't seek out a fight.

We created this article in conjunction with AI technology, then made sure it was fact-checked and edited by a HowStuffWorks editor.