Name: 三幕爬行动物的时代（The Age of Reptiles in Three Acts）
Uploaded: 2021-04-30T13:34:44.000Z
Duration: 11 min 7 s
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A quarter of a billion years ago, an epic story was starting to unfold all over the

The heroes of this saga were the survivors of a near apocalypse.

They emerged from it as humble creatures, but in time, they came to dominate the Earth.

These were the reptiles, which grew to become some of the largest forms of life ever to

There were, however, some other noteworthy players in this story -- the animals and plants

that diversified in the shadows of the reptiles, many of which would go on to play key roles

Over millions of years, this whole troupe of characters adapted to a rapidly

But, even though they grew to immense sizes and dominated all environments, many of the

reptiles couldn't adapt to the changes that would bring their reign to an end.

This Age of Reptiles was a spectacular prehistoric epic, and it all took place in a single era:

The Mesozoic Era began 252 million years ago in the aftermath of the most destructive mass

It brought to a close the previous era, the Paleozoic, and wiped out most marine and land

species, leaving a world ripe for the taking, at least for … anything that survived.

In the Early Mesozoic, Earth's landmasses had almost finished merging into a single

And that meant life could traverse the globe, free of ocean barriers.

The stage was set for the first act of the Mesozoic, the Triassic Period.

At first, the planet was populated only by the survivors of the Paleozoic.

On land, there were the amphibian-like temnospondyls and early relatives of mammals called therapsids.

Meanwhile, the seas were home to many groups of ancient fish but also lots of reptiles

These first marine reptiles were mostly amphibious, but they quickly developed fully aquatic traits,

including the ichthyosaurs, which came to resemble fish and later marine mammals, even

And in the background, a special group of reptiles was beginning to take advantage of

These were the archosaurs, a clade that had its origins in the Paleozoic but truly came

Archosaurs include many of the animals that you think of, when you think of ancient life

-- like dinosaurs, pterosaurs, and the croc-like phytosaurs.

And these creatures became key players in the Mesozoic, because they were very well

The skulls of archosaurs were lighter than their reptile ancestors.

Most archosaurs also had teeth that were set in deep, protective sockets.

Plus they pioneered a unique unidirectional respiratory system which was a network of air sacs

that let them breathe more efficiently in the low-oxygen atmosphere after the Great

With the help of adaptations like these, archosaurs spread and diversified.

And by the middle of the Triassic, around 243 million years ago, the real rising stars

of the archosaurs appeared: the first dinosaurs.

This is when the earliest known proto-dinosaur appears in the fossil record: Nyasasaurus,

Soon after, we find evidence of the tiny omnivore Eoraptor and the predator Herrerrasaurus,

And all of the earliest known dinosaurs were members of the same group, known today as

They had the same basic things in common, like long necks and tails and a generally

But the thing I wanna point out here is their … pubis.

That's one of the three bones that makes up the pelvis, including in you.

And in the case of saurischian dinosaurs, the pubis bone always pointed down, and forward.

I know it'll be hard for ya, but try to remember that word, pubis, because I'm gonna

Now, as dinosaurs started playing larger roles in their ecosystems, they also became larger

And around 230 million years ago, they diverged into two of their most iconic groups: the

long-necked sauropods and the two-legged, mostly-meat-eating theropods.

But while dinosaurs were becoming more diverse and widespread, another lineage of archosaurs

was adapting to another environment: the sky.

By the Late Triassic, pterosaurs became the first vertebrates in the history of the world

to take flight, with Eudimorphodon and others like it appearing in the fossil record throughout

Meanwhile, other, non-archosaurian reptiles were dominating the seas.

Ichthyosaurs had been swimming the world's oceans since near the start of the Triassic.

And by 200 million years ago, another group of semi-aquatic reptiles had given rise to

plesiosaurs, which adopted a totally different body plan for life in the water.

This three-pronged takeover of the land, sea, and sky allowed the reptiles to rule Pangea.

But it was not until the very end of this period that the last remnants of Paleozoic

201 million years ago, Pangea began to break apart, as North America drifted away from

This caused a spike in volcanic activity that sent greenhouse gases into the atmosphere.

The resulting rise in global temperatures triggered an event known as the End-Triassic

The casualties included most of the therapsids and other holdovers from the Paleozoic.

And this left many niches open for the dinosaurs, pterosaurs, and other reptiles that would

Which brings us to the second act of this story: the Jurassic Period, when the Age of

By this time, dinosaurs had already acquired a variety of body plans and adaptations.

And one of the most important was the spread of the Ornithischians

Now, remember that pelvic bone I was talking about?

Well that's where a major change occurred in ornithischian dinosaurs.

Instead of pointing down and forward, in ornithischians, the pubis was reversed.

This allowed ornithischians to have a larger gut cavity that could hold expanded digestive

organs, and this helped them eat some of the toughest plants of the Mesozoic.

Because of this adaptation, and with the help of new, chisel-like teeth, ornithischians

became the eating machines of the Mesozoic!

Ornithischians probably first appeared back in the Triassic, but this was when they started