Meet the world's first dinosaur.

No, down here.

Eoraptor would have only come up to about your knees.

In fact, most early Triassic dinosaurs were on the shrimpy side, including predators like the fierce, mule-sized Coelophysis.

But after volcanic eruptions took out their competitors and ushered in the Jurassic period, everything changed.

New species exploded onto the scene like the plate-covered Scelidosaurus.

And bigger herbivores meant bigger meat eaters too.

Predators, like the Dilophosaurus got to be six meters long.

But they were no match for the real giants of the era, Prosauropods.

Now, these leaf eaters weren't much bigger than a giraffe.

On the inside, they looked like a bird.

And it's this anatomy that enabled Prosauropods to evolve into the largest dinosaurs of all time.

So let's take a closer look.

Specialized lungs and air sacs allowed them to take in more oxygen and also made their skeletons lighter, hollowing out bone into a sturdy, honeycomb structure.

Millions of years of evolution later, you can see the difference.

Ornithischian dinosaurs like Triceratops and Stegosaurs lack these air sacs and as a result, most of them weren't very big.

While Triceratops and Stegosaurus grew up to eight meters long, bird-like theropods like Tyrannosaurus grew twice as large.

But it was the sauropods like Brontosaurus, Diplodocus and Brachiosaurus who reached enormous proportions.

Like the theropods, these titans used air sacs to breathe and had light, hollow bones.

But they had another reason for outgrowing everyone else at the time: survival.

Their size was a great defense against predators and the largest of the bunch stood over 26 meters long, weighed 55 tons or more,

and could reach several stories up with their long necks which came in handy for gathering enough food.

After all, you can't grow this big without a lot of energy.

In fact, Brontosaurus ate about 45 kilograms of leaves, stems, and twigs a day.

But they couldn't waste energy hunting around to find those veggies.

Instead they parked themselves in one spot for hours and used their long necks to graze up and down, stripping trees like a giant corn on the cob.

And the more these animals sat around and ate, the bigger they became.

Tens of millions of years later, we see another bird-like dinosaur enter the stage.

Titanosaurs, the largest dinosaurs in history.

Dreadnoughtus, Patagotitan, and Argentinosaurus could stand over 20 meters long.

But of course, their height couldn't save them from the asteroid strike.

And there's been nothing like them since, at least on land anyway.