One of the most popular dinosaurs of the Late Cretaceous was found in what is now Montana, Wyoming, Colorado, and South Dakota. We're talking about the Triceratops, known for its large bony ridge on the back of its head and its three horns. Despite being a herbivore, the Triceratops was huge, weighing between 6 and 12 tons and growing up to 30 feet in length and 10 feet in height!

Image: K. Mitch Hodge

The Allosaurus lived approximately 150 million years ago, and its fossils were found in the areas occupied today by the states of Colorado, Wyoming, and Utah. With a size that could reach 39 feet in length and weighing about 2.5 tons, Allosaurus was a massive bipedal carnivore, which means it walked on two large, strong hind legs!

Image: The frolicsome Fairy

If there was one creature that looked truly prehistoric, it was the Ankylosaurus, which lived around 66 million years ago and roamed the areas now known as Montana and Wyoming. It could grow up to 30 feet long and weigh about 8,000 pounds! It was herbivorous, but its body was like a tank, covered with thick bony plates and protective spikes.

Image: Blond Fox

Now it's the turn of a very special specimen: the Ornithomimus. This peculiar dinosaur, whose fossils were found in the western United States, was light and fast. It weighed up to 300 pounds, not much compared to its colleagues. It looked more or less like an ostrich, and scientists believe it even had feathers on its forelimbs.

Image: Tina Hartung

Coelophysis was another bipedal dinosaur that lived about 210 million years ago. Fossils of this species have been found in what is now New Mexico, Arizona, and other parts of the American Southwest. Unlike Allosaurus, Coelophysis was small, light, and fast, measuring between 6 and 10 feet in length and weighing roughly 60 pounds.

Image: Kvnga

The incredible Maiasaura lived about 75 million years ago and was discovered in North America, specifically in Montana. It was a duck-billed herbivore, and according to research, it devoted a lot of time and dedication to the care of its eggs. In fact, its name means "Good Mother Lizard." Cute, isn't it?

Image: Yena Kwon

Deinonychus is the name of this dinosaur that lived around 110 million years ago, with fossils discovered mainly in Montana, Wyoming, and Oklahoma. This carnivore is believed to have hunted in packs—a behavior that, if true, would have made it even more terrifying!

Image: Jossuha Théophile

We return to the "-saurus" with Stegosaurus, whose image is one of the most iconic, thanks in part to movies. Yes, it’s the big dinosaur with a long tail and bony plates running along its back. This 7-ton animal’s fossils have been found in Colorado, Utah, and Wyoming. Despite its massive size and weight, Stegosaurus had a very small brain.

Image: Lucas George Wendt

Diplodocus was one of the largest dinosaurs ever to walk the Earth, and its footsteps left their mark in the lands of Colorado, Wyoming, Montana, and Utah. It could reach up to 100 feet in length, thanks in part to its incredibly long neck, and weighed between 15 and 30 tons. Yes, it’s the dinosaur that reminds many people of the Loch Ness Monster!

Image: Arthur Shuraev

We saved the best for last. The star of the dinosaurs is undoubtedly the popular Tyrannosaurus rex, or T. rex for friends. Its fossils have been discovered mainly in the western United States. This huge dinosaur lived between 70 and 66 million years ago and had an imposing body: it could reach 40 feet in length, stand 12 feet tall at the hips, and weigh an incredible 8 tons—as much as a bus!

Image: Tofan Teodor