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Experts are still arguing over whether Archaeopteryx was a true bird, or a paravian dinosaur, or some other kind of dino. But regardless of what side you’re on, how did this fascinating, bird-like animal relate to today’s birds? It turns out its teeth were a clue that this story goes all the way back to what we now call the non-avian dinosaurs.

The ancestors of modern horses became so successful that they spread all over the world, to Europe, Asia, South America, and Africa. But in their native range of North America, they’ll vanish for 10,000 years. Until another strange mammal brings them back.

One of the most dynamic, transformative, and potentially dangerous features in North America is also responsible for some of the continent’s most amazing fossil deposits. It’s a supervolcano we now call Yellowstone.

A huge and diverse subfamily of dogs, the bone-crushers patrolled North America for more than thirty million years, before they disappeared in the not-too-distant past. So what happened to the biggest dogs that ever lived?

If you take it as a given that extinct dinosaurs were all weird and wonderful, then you gotta at least consider that Stegosaurus was one of the weirdest and wonderfulest.

We know a lot about dinosaurs but there’s one question that has plagued paleontologists for decades: what color were they?

Smilodon was a fearsome Ice Age cat, the size of a modern-day tiger, that had a pair of fangs nearly 18 centimeters long. But it was only the last and largest of the great sabertooths: ridiculously long canines had already been a trend for millions of years by the time Smilodon was prowling around. And you know what? Those giant teeth just might make a comeback.

What if we told you that there was a time when oxygen almost wiped out all life on Earth? 3 billion years ago, when the world was a place you’d never recognize, too much of a good thing almost ruined everything for everybody.

Today, we’re familiar with two types of flying vertebrates -- birds and bats. But over 66 million years ago, there was a giraffe-sized reptile that soared through the sky.

With its lizard-like appearance and that distinctive sail on it back, Dimetrodon is practically the mascot of the Palaeozoic Era, a time before flowers, birds, mammals, and even crocodiles. But if you take a close look at this sail-backed animal, you might see a little bit of yourself.

Natural history is full of living things that were long thought to have gone extinct only to show up again, alive and well. Paleontologists have a word for these kinds of organisms: They call them Lazarus taxa.

There are many fossils that challenge our ability to form even the most basic idea of how a living thing looked, or lived, or functioned. One of the longest-running of these mysteries involved a 270-million-year-old sea creature called Helicoprion that once swam the seas around the supercontinent of Pangea.

Insects outnumber humans by a lot and we only like to think we're in charge because we're bigger than they are. But insects and other arthropods weren’t always so small. About 315 million years ago during the Carboniferous Period, they were not only abundant: they were enormous.

Fossil fuels are made from the remains of extinct organisms that have been exposed to millions of years of heat and pressure. But in the case of coal, these organisms consisted largely of some downright bizarre plants that once covered the Earth, from Colorado to China.

Part of why we’re so fascinated with extinct dinosaurs it’s just hard for us to believe that animals that huge actually existed. And yet, they existed! From the Jurassic to the Cretaceous Periods, creatures as tall as a five-story building were shaking the Earth.

Besides the blue of the oceans, the dominant color of our planet, as we know it, is green. But imagine a time when the Earth looked a little … purple.

Crocodiles, horseshoe crabs and tuatara are animals that have persisted for millions of years, said to have gone unchanged since the days of the dinosaurs. But even the most ancient-looking organisms show us that evolution is always at work.

We know whales as graceful giants bound to the sea. But what if we told you there was actually a time when whales could walk.

Our image of dinosaurs has been constantly changing since naturalists started studying them about 350 years ago. Taken together, these pictures can tell us a whole lot about just how much we have learned. Let's explore the history of dinosaur science as seen through the history of dinosaur art.

By looking at the layers beneath our feet, geologists have been able to identify and describe crucial episodes in life’s history. These key events frame the chapters in the story of life on earth and the system we use to bind all these chapters together is the Geologic Time Scale.

More than 4 billion years ago, the crust of the Earth was still cooling and the oceans were only beginning to form. But in recent years, we’ve started to discover that, even in this hellish environment, life found a way.

Over the past 20 years, dinosaurs of all types and sizes have been found with some sort of fluff or even full-on plumage. These fuzzy discoveries have raised a whole batch of new questions so we're here to tell you everything we know about dinosaurs and feathers.

Imagine an enormous, lush rainforest teeming with life...in the Arctic. Well there was a time -- and not too long ago -- when the world warmed more than any human has ever seen. (So far)

Probably twice the size of a modern gorilla, Gigantopithecus is the greatest great-ape that ever was. And for us fellow primates, there are some lessons to be learned in how it lived, and why it disappeared.

420 million years ago, a giant feasted on the dead, growing slowly into the largest living thing on land. It belonged to an unlikely group of pioneers that ultimately made life on land possible -- the fungi.