When you think of fossils and prehistoric times, what do you think of? If you're like most kids, you probably think of the wide variety of “terrible lizards" we know as dinosaurs.

Dinosaurs still fascinate kids and adults alike today. It's so much fun to imagine what life must have been like on Earth millions upon millions of years ago, when Tyrannosaurus Rex and hundreds of other types of dinosaurs roamed Earth.

But were dinosaurs the first living things on Earth? Or were there other animals on Earth long before the dinosaurs ruled the world? Although dinosaurs did indeed rule Earth for millions of years, there were animals that roamed the world long before they did.

In fact, hundreds of millions of years before the dinosaurs ruled, life existed on Earth in the form of some interesting and strange creatures. Way back then, during what scientists call the Carboniferous period, Earth was covered in hot, humid swamps and rainforests. These harsh conditions gave rise to a variety of strange creatures, many of which were large amphibians (creatures that lived on both land and in the water).

One of the bizarre creatures that inhabited those swamps was Diploceraspis. Just imagine a salamander that stretched three feet long with a head shaped like a boomerang and you'll have an idea of what Diploceraspis looked like when it traveled through the swamps.

In addition to large, strange amphibians, the Carboniferous period was also known for some other curious forest residents: gigantic insects! During the Carboniferous period, Earth's atmosphere had much more oxygen than it does today. This bounty of oxygen allowed for much larger flying creatures, especially insects.

For example, Meganeura was a giant dragonfly that inhabited the swamps of Earth. If you've ever seen a modern dragonfly, you know they can be much larger than a typical insect, such as a mosquito or a fly. However, Meganeura might have been the size of a large bird, such as an eagle!

If Meganeura sounds like quite a sight, then you would also be amazed by Arthropleura. Arthropleura was a giant centipede that likely stretched to lengths of eight feet or more. And if those gigantic centipedes and dragonflies the size of birds weren't weird enough, scientists believe there were also spiders the size of cats!

Over time, larger reptiles began to evolve as the climate became hotter and drier. Reptiles, such as pelycosaurs, archosaurs, and therapsids, bridged the gap between the bizarre amphibians of the Carboniferous period and the first dinosaurs.

One such creature was Dimetrodon, a meat-eating predator with a huge sail on its back. Scientists believe the huge sail may have been used to help Dimetrodon warm up faster in the morning, allowing it to feed on other rainforest animals before they got up and got going.

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