Name: A Brief History of Life: Dinosaur Time!
Uploaded: 2021-04-27T06:35:33.000Z
Duration: 9 min 10 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

Welcome to the third installment of our miniseries on the history of life on Earth!

Advanced passive voice

When we left off, life had been brought to its knees by a mass extinction at the end

The Mesozoic era, from 251 to 65 million years ago, followed the great extinction and would

produce some of the weirdest and most fascinating animals of all time.

It also led to most of the major land animal groups we know today.

Like other eras, the Mesozoic is divided into periods -- in this case, three of them.

The first period, the Triassic, lasted from 251 to 199 million years ago.

It was a time of transition, when the dominant vertebrates of the late Paleozoic, the therapsids,

A new group of reptiles, the dinosaurs, then rose to become Earth's new dominant land vertebrates.

Throughout the Mesozoic, Earth was warmer than it is now, and had no polar ice caps.

At the beginning of the Triassic, Earth's landmasses were lumped together into the dry

Slowly, life started to repopulate the place.

The therapsids were declining, but a new group of vertebrates was starting to take over -- the

Archosaurs descended from one of the earliest major groups of land vertebrates, the diapsids,

These major animal groups -- the archosaurs and the diapsids -- are defined by the holes

in their skulls, which attach to muscles and mean that the big, heavy bones weigh a little less.

It might seem like kind of a strange way to tell animals apart, but it's actually a

Diapsids have two openings behind their eyes.

Archosaurs have two extra openings, one in front of the eye and one in the lower jaw.

Dinosaurs are archosaurs, but so is another group that almost took over instead of the

dinosaurs: the pseudosuchians, which evolved very similar body plans to the dinosaurs that

came later -- including standing on two legs.

They came in a lot of different shapes and sizes, but if you want know what a pseudosuchian

looked like, picture something a bit like a crocodile, but about twelve times more terrifying,

because it's able to stand up straight on long legs and run really fast over land.

Pseudosuchians were nearly wiped out in another mass extinction at the end of the Triassic.

Only one lineage survived, one that took to living in swamps and gave rise to modern crocodiles

Although thankfully, the modern versions don't run around on two legs.

The only other archosaurs around today are birds.

So the archosaurs took over from the therapsids, which had mostly died out at the end of the Paleozoic.

But some therapsids hung on through the Triassic, and some didn't die out at all -- luckily for us.

The therapsids are the descendants of another major branch of land vertebrates, the synapsids,

who are also classified by their skull holes.

Synapsids have one skull opening, not four, and they're the ancestors of mammals.

The earliest mammals appeared in the middle of the Triassic -- at practically the same

Yes -- we mammals started out as dinosaur buddies, and we still hang out with dinosaurs

Speaking of dinosaurs: there probably weren't many Triassic dinos in the coloring books

you had when you were six, because they hadn't developed much yet.

But they had some advantages that would eventually make them the ruling reptiles.

Like I mentioned earlier, pseudosuchians and dinosaurs had very similar body plans.

But dinosaurs had a slight physiological edge: their breathing was more efficient.

And while both groups evolved legs that were positioned straight under them instead of

sprawling to the sides, dinosaurs were the stronger movers.

The earliest dinosaurs that we can be confident about go back 230 million years.

But there are some very dino-like animals from 10 million years before that.

An animal called Nyasasaurus may or may not be a true dinosaur, depending on who you ask,

And it comes from 243 million years ago in present-day Tanzania.

As is often the case with evolution, it's hard to draw the line between true dinosaurs

But somewhere between Nyasasaurus and later dinosaurs like Eoraptor, they had officially

A couple of other animal groups turned up during the Triassic.

One was the ichthyosaurs, the first reptile group to become fully aquatic again after

They're also one of only two groups to evolve a fish-shaped body from a four-footed animal body.

Finally, toward the end of Triassic, a group of archosaurs that were closely related to

the dinosaurs -- but weren't dinosaurs themselves -- evolved the power of flight: the pterosaurs.

After the Triassic came a period that you might have heard of: the Jurassic period,

which lasted from 199 to 146 million years ago.

Although I do feel like I need to point out that some of the dinosaurs in the movie franchise

are partly or totally made up, and others aren't from the Jurassic at all.

During the Jurassic, Pangea was beginning to separate into two continents, Laurasia

This is when dinosaurs diversified into their more familiar forms.

The Jurassic was a great time to be a sauropod, for example: a huge, long-necked plant-eater

Diplodocus, Brachiosaurus, and Apatosaurus all lived during the Jurassic.

Then there were the theropods, the meat-eaters that walked upright.

Allosaurus was one major predator, but even bigger and meaner theropods were yet to come.

The Stegosaurus also evolved during the Jurassic.

It was a big plant-eater with plates all along its back and a spiked tail weapon called a

thagomizer, because if you're going to pick a name for a giant spiky tail-weapon you might

Meanwhile, the Plesiosaurs, a group of reptiles not closely related to dinosaurs, joined ichthyosaurs

There was one other major group of dinosaurs that appeared in the Jurassic: birds.

We know that birds are descended from dinosaurs because of the similarities of their skeletons,

and the fact that many dinosaurs had feathers.

And because people who study evolution like to include all of a group's descendents

in that group, birds technically are dinosaurs.

So, if you've ever fed a chicken nugget that's shaped like a dinosaur to a child:

Archaeopteryx, which is usually considered the earliest bird, dates back to the Jurassic,

They, along with the pterosaurs, were the two kinds of flying archosaurs during the