Why Triassic Animals Were Just the Weirdest

Summary

The script explores the Triassic Period's drepanosaurs, reptiles resembling chameleons but with bird-like heads. Once thought to be bird ancestors, they were revealed as early reptilian lineage through skull analysis. The Triassic's unique fauna, evolving rapidly between mass extinctions, exemplifies adaptive radiation as species filled new ecological niches. This pattern of extinction and evolutionary innovation continues, shaping life's diversity.

Takeaways

• 🐾 Drepanosaurs were reptilian creatures from the Triassic period, resembling chameleons with bird-like heads and beak-like features.
• 🕵️‍♂️ Initially mistaken for early birds, further study revealed drepanosaurs were an early reptile lineage, distinct from birds.
• 🌿 The Triassic period was home to many creatures with body plans that would reappear in unrelated species much later.
• 🔍 The first drepanosaur, Drepanosaurus unguicaudatus, was identified in the late 1970s from fossils found in Italy.
• 🧬 The Triassic period's unique evolutionary patterns were influenced by the mass extinctions at its start and end, allowing for rapid evolutionary changes.
• 🌋 The Great Dying and End Triassic Extinction events created opportunities for species to evolve and fill newly available ecological niches.
• 🌱 Drepanosaurs adapted to a tree-climbing insectivore niche, developing unique features like grasping hands and flexible necks.
• 🐊 Phytosaurs, another Triassic reptile, evolved to fill the role of river-dwelling fish-eaters, developing long, narrow snouts.
• 🦕 The End Triassic Extinction led to the rise of dinosaurs, which filled the ecological niches left by the extinct Triassic animals.
• 🌿 After mass extinctions, life often rebounds through adaptive radiation, where new species rapidly evolve to fill empty niches.
• 🌎 The pattern of extinction followed by evolutionary bursts is a recurring theme in Earth's history, suggesting it will continue into the future.

Q & A

What are drepanosaurs, and why were they considered strange by paleontologists?

Drepanosaurs were strange-looking reptiles that lived 220 million years ago, resembling a mix of chameleons, birds, and other reptiles. They had grasping hands, prehensile tails, bird-like heads, and sometimes beaks, making them difficult to categorize. For a long time, paleontologists were unsure how to classify them due to their mix of traits.

Why were drepanosaurs initially thought to be related to birds?

Drepanosaurs were thought to be related to birds because of their bird-like heads, long necks, and beak-like mouths. These features led some researchers in the 1990s to speculate that they were connected to early bird evolution, despite their overall body shape being very different from birds.

What did the discovery of the Avicranium skull in 2017 reveal about drepanosaurs?

The discovery of the Avicranium skull in 2017 clarified that the bird-like appearance of drepanosaurs was superficial. The skull showed that their ears resembled those of early reptiles, not birds, and confirmed that drepanosaurs were part of an early branching lineage of reptiles, not related to birds.

What is convergent evolution, and how does it relate to the Triassic period?

Convergent evolution occurs when unrelated species develop similar traits due to similar environmental pressures. During the Triassic period, many animals, like phytosaurs and ichthyosaurs, evolved body plans that resembled later species, such as crocodiles and porpoises, despite not being closely related to them.

Why did the rate of evolutionary change appear to be faster during the Triassic period?

The rate of evolutionary change appeared faster during the Triassic because the period followed the Great Dying mass extinction, which left many ecological niches empty. With less competition, surviving species rapidly evolved to fill these niches, leading to adaptive radiations and new species.

How did the lack of competition influence evolutionary changes during the Triassic?

The lack of competition during the Triassic allowed for rapid evolutionary change. When niches were empty, new species evolved to fill them quickly, without being constrained by existing species. This led to a variety of unique adaptations in animals like drepanosaurs.

What caused the extinction of drepanosaurs at the end of the Triassic period?

Drepanosaurs, along with many other species, went extinct at the end of the Triassic due to a combination of volcanic activity and the breakup of Pangaea. This led to rapid global warming, ocean acidification, and ultimately wiped out about three-quarters of all species on Earth.

What role did adaptive radiation play after the extinction events in the Triassic?

Adaptive radiation occurred after the mass extinctions in the Triassic, as surviving species rapidly evolved to fill the empty niches left by the extinct species. This process led to the diversification of species and the appearance of new body plans, such as dinosaurs evolving to replace earlier reptiles.

How does the story of drepanosaurs illustrate the concept of evolutionary innovation after mass extinctions?

Drepanosaurs illustrate the concept of evolutionary innovation because they evolved rapidly after the Great Dying, filling a tree-climbing insectivore niche. Their unusual body structures, such as chameleon-like hands and bird-like heads, show how organisms can evolve quickly to adapt to new roles when competition is low.

How did the end-Triassic extinction pave the way for the rise of dinosaurs?

The end-Triassic extinction wiped out many dominant species, including drepanosaurs and phytosaurs, creating empty ecological niches. Dinosaurs, which were small and less specialized, survived and rapidly evolved to fill these niches, leading to their dominance in the Jurassic and beyond.

Outlines

00:00

🦎 Early Reptiles and the Mystery of Drepanosaurs

This paragraph discusses the discovery and characteristics of drepanosaurs, an ancient reptile species from the Triassic Period. These creatures resembled chameleons but had bird-like heads and beaks. Paleontologists initially struggled to classify them due to their unique features, which were unlike any other reptiles. Drepanosaurs were not closely related to birds, which appeared much later. The Triassic Period was noted for its diverse creatures, some of which resembled modern species but were not their ancestors. The paragraph also delves into the evolutionary changes in drepanosaurs, from their initial discovery in the 1970s to the realization that they were an early branching lineage of reptiles. The Triassic's position between two mass extinctions is highlighted as a key factor in the rapid evolutionary changes observed in drepanosaurs and other species of the time.

05:01

🌿 Adaptive Radiation and the Aftermath of Extinctions

The second paragraph explores the concept of adaptive radiation, which is the rapid evolution of new species following mass extinctions. It explains how the Triassic Period, situated between two major extinction events, allowed for an explosive diversification of life as species filled newly available ecological niches. Drepanosaurs, for instance, evolved to become adept at climbing trees and eating insects. The paragraph also discusses how competition regulates evolutionary change, with less competition leading to faster evolutionary rates. The narrative then shifts to the End Triassic Extinction, which wiped out many species, including drepanosaurs, and set the stage for dinosaurs to thrive. The paragraph concludes with a reflection on the cyclical nature of mass extinctions and adaptive radiations throughout Earth's history, emphasizing the resilience of life and its ability to evolve and diversify.

Keywords

💡Drepanosaurs

Drepanosaurs were a group of reptiles that lived during the Triassic period. They had unique features such as grasping hands and feet, long prehensile tails, and small bird-like heads. The term is central to the video's theme as it discusses how these creatures evolved and how their physical characteristics were initially puzzling to paleontologists. The script mentions that drepanosaurs were initially thought to be related to birds due to their bird-like heads and necks, but further research showed they were an early branching lineage of reptiles.

💡Adaptive Radiation

Adaptive radiation refers to the rapid diversification of species from a common ancestor into a variety of forms to exploit new ecological niches. It is a key concept in the video, illustrating how life can rapidly evolve and diversify after mass extinctions. The script uses the example of drepanosaurs to show how they evolved from lizard-like ancestors to fill the niche of tree-climbing insectivores after the Great Dying.

💡Triassic Period

The Triassic Period is a geological time period between the Permian and Jurassic periods. It is significant in the video's narrative as it was a time of significant evolutionary change and the setting for the rise of various species like drepanosaurs. The Triassic is described as a time 'trapped between two mass extinctions', highlighting its role in the adaptive radiation of species.

💡Mass Extinctions

Mass extinctions are events that result in the widespread and rapid die-off of species. The video discusses two major mass extinctions that bookend the Triassic Period: the Great Dying (Permian-Triassic extinction event) and the End Triassic Extinction. These events are crucial to understanding the video's theme of how life on Earth recovers and evolves after遭受重创.

💡Convergent Evolution

Convergent evolution is the process by which unrelated species develop similar traits or body plans as a result of having to adapt to similar environments or ecological niches. The video uses the example of how the body plans of some Triassic reptiles reappeared in unrelated species later in time, illustrating how evolution can produce similar outcomes independently.

💡Ecological Niches

Ecological niches are roles that organisms play in their environment, including how they acquire resources and interact with other species. The video explains how the mass extinctions during the Triassic Period created many empty ecological niches, allowing for rapid evolutionary change and the rise of new species like drepanosaurs.

💡Pangaea

Pangaea was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. The video mentions that drepanosaurs lived in the forests of northern Pangaea, providing a geographical context for where these creatures evolved. Pangaea's breakup is also tied to the End Triassic Extinction, which is part of the video's narrative on extinction and recovery.

💡Phytosaurs

Phytosaurs were a group of semi-aquatic reptiles that lived during the Triassic Period. They are mentioned in the video as an example of creatures that looked similar to modern species (like crocodiles) but were not closely related to them. This illustrates the concept of convergent evolution discussed in the video.

💡Ichthyosaurs

Ichthyosaurs were marine reptiles that resembled porpoises. The video uses ichthyosaurs to further demonstrate how the Triassic Period was home to creatures that looked similar to later species but were not their ancestors, emphasizing the theme of convergent evolution.

💡CuriosityStream

CuriosityStream is a streaming service that supports PBS Digital Studios, as mentioned in the video's introduction. It is relevant as it provides context for the video's production and the platform on which it is hosted, indicating the source of the content and its association with educational media.

💡Selective Pressures

Selective pressures are influences in the environment that favor certain traits over others, leading to their increased prevalence in a population over time. The video discusses how similar selective pressures can lead to similar body plans in different species, as seen in the convergent evolution of Triassic reptiles and their later counterparts.

Highlights

Drepanosaurs were reptiles that lived 220 million years ago in the forests of northern Pangaea.

They resembled chameleons but had small, bird-like heads and beaks.

Paleontologists were initially perplexed by their unique features.

Drepanosaurs were once thought to be close ancestors of birds.

The Triassic Period was filled with animals resembling modern species but not closely related to them.

Drepanosaurs were unknown until the late 1970s when the first species was named based on fossils found in Italy.

They had grasping hands, arched backs, and thick muscular tails.

Some drepanosaurs had prehensile tails with a claw-like hook.

Their heads had pointed snouts, big eyes, and sometimes beaks instead of teeth.

In the 1990s, some researchers believed drepanosaurs were related to the early evolution of birds.

In 2017, a new drepanosaur species named Avicranium was discovered, clarifying their relationship with other reptiles.

Drepanosaurs were one of the earliest branching lineages of reptiles, diverging late in the Permian Period.

The Triassic Period was a time of rapid evolutionary change due to two major extinction events.

Drepanosaurs adapted to a specific niche as tree-climbing insectivores.

Adaptive radiations, bursts of evolutionary change, occurred after mass extinctions.

The End Triassic Extinction wiped out about three quarters of the world's species, including drepanosaurs.

Dinosaurs were the big winners after the End Triassic Extinction, filling the ecological niches left by Triassic animals.

Convergent evolution led to similar body plans in dinosaurs that replaced earlier species.

After the extinction of non-avian dinosaurs, mammals and birds experienced a rapid burst of evolutionary change.

Life continues to evolve through adaptive radiations following mass extinctions.

Transcripts

Thanks to Curiosity Stream for supporting PBS Digital Studios.

220 million years ago, some strange-looking reptiles lived in the forests of northern

Pangaea.

They looked kind of like chameleons, with grasping hands and feet, and long prehensile

tails.

But they also had really small, bird-like heads, and sometimes beaks, and

these cool spikes sticking out of the ends of their tails.

These were drepanosaurs.

And for a long time, paleontologists didn’t know what to make of them.

Sure, they look kinda like chameleons, but their heads are all wrong, not at all like

other reptiles.

And chameleons don’t show up in the fossil record for another 120 million years after

these guys.

So, for a long time, some experts thought these animals were close ancestors of birds.

I, myself, don’t see it.

But it turns out, the Triassic was full of animals like this -- creatures that look a

lot like other, more modern species, even though they’re not closely related to them

at all.

In addition to the drepanosaurs, the Triassic was home to the phytosaurs, which could easily

be mistaken for crocodiles.

And ichthyosaurs, which looked a whole lot like porpoises, even though they were reptiles.

There was a host of creatures whose basic body plans would show up again and again,

much later in time, by completely unrelated species.

So why were the animals of the Triassic like this?

What made them look like animals that lived much later, and that they weren’t related

to?

The answer has to do with how evolution works, and with the timing of the Triassic itself,

when life was trapped between two mass extinctions.

Drepanosaurs were unknown to scientists until the late 1970s, when the first species, Drepanosaurus

unguicaudatus, was named, based on fossils found in Italy.

And since then, only a handful of others have been named, all from Triassic rocks in the

northern hemisphere.

Scientists originally thought that drepanosaurs were just weird, early lizards.

But the more they looked at them, the more confusing they became.

These creatures had grasping hands, arched backs, and thick muscular tails.

Some kinds, like Megalancosaurus, even had prehensile tails, with a claw-like hook on

the end that helped them hold on to branches.

And the heads on these animals weren’t like those on other reptiles.

They had pointed snouts, big eyes, and sometimes beaks instead of teeth, making them look less

like lizards and more like … featherless birds.

Their necks were bird-like, too, with vertebrae that were saddle-shaped, giving them a greater

range of motion.

Now, because their heads and necks were so bird-like, some researchers in the ‘90s

thought that drepanosaurs must have had something to do with the early evolution of birds themselves,

despite the fact that the rest of their bodies looked nothing like birds.

But in 2017, things started to become more clear, when the pristine skull of a new drepanosaur

species was reported in New Mexico.

The new genus was named Avicranium, or “bird head,” and it brought the relationship between

drepanosaurs and other reptiles into sharper focus.

It turned out that any resemblance this drepanosaur had to birds was really pretty superficial.

Its ears for instance, lacked ear drums and were more like the ears of early reptiles

than those of birds.

In fact, researchers compared more than 300 of its anatomical features with other early

reptiles, and concluded that drepanosaurs were one of the earliest branching lineages

of reptiles, probably diverging late in the Permian Period.

And like all early reptiles, the ancestors of drepanosaurs probably looked superficially

like lizards, even though they weren’t closely related to them.

They had short necks, low-slung bellies, and long tails, with limbs sticking out from the

sides of the body.

So, what happened to them?

How did drepanosaurs go from being pretty familiar lizard-like reptiles to animals so

strange that it took experts decades to figure out what they were?

And how did these changes happen in such a short span of time?

It’s because the Triassic was basically the meat in an extinction sandwich.

The entire Triassic Period is a window of just 52 million years, between two major extinction

events.

At the early end, there was the Great Dying, which eradicated about 70% of terrestrial

species and 90% of marine life.

On the other end, there was the aptly-named End Triassic Extinction, which wiped out more

than half of animal species.

But in between, there was the whole, wide, still-mostly-liveable world.

And for the survivors of the Great Dying, this was a completely different world -- one

with a whole host of ecological niches that needed to be filled.

And at the same time, there was almost no competition.

And in any given environment, it’s competition that usually regulates the rate of evolutionary

change among living things.

By and large, the less competition there is, the faster the rate of change will appear

to be.

That’s because a lack of competition allows empty niches in an ecosystem to be filled

by new species.

Then, over time, as those niches fill up, competition increases, and the rate of evolutionary

change appears to slow down.

I say it “appears to,” because genetic mutations keep showing up like they always

do.

But if those mutations don’t offer big advantages right away, they get weeded out, and body

plans keep looking basically the same.

So, if you’re an animal that’s found your niche -- say, preying on fish in rivers -- then

natural selection tends to let you keep doing what you’re doing.

Your rate of evolutionary change, at least outwardly, appears to be slow, because you’ve

found a body plan that works.

Likewise, it’s hard for other lineages to move into that role.

So, natural selection usually leads them to keep doing what they’re doing, too, rather

than try to compete directly for a niche that’s already been filled.

But!

When extinctions occur, the opposite happens!

Lots of niches open up, and there’s much less competition.

There’s plenty of room for everyone.

And that’s when the rate of evolutionary change takes off.

Organisms quickly move into unfilled niches and diversify into new species, as they arrive

at the adaptations that help them succeed in certain roles

These explosive bursts of evolutionary change are known as adaptive radiations, and they

typically happen after mass extinctions.

And this is exactly what happened to drepanosaurs, and other reptiles at the start of the Triassic.

Before the Great Dying, in the Permian, the ancestors of all reptiles looked pretty lizard-like,

and they filled similar niches that many lizards do today.

But the earliest members of the drepanosaur line started to adapt to a specific niche

-- that of tree-climbing insectivores.

And within just 20 million years, the first drepanosaurs appear in the fossil record as

their own distinct lineage of reptile.

Those chameleon-like hands and feet helped them climb trees.

The arched shoulders and flexible necks may have helped them catch bugs or peel away tree

bark.

And their bird-like heads and beaky mouths allowed them to probe tight spaces for food.

As the Triassic wore on, more empty niches were filled, and the rate of evolutionary

change, and the appearance of new species, slowed down.

Soon, a new normal was established.

For example, some lineages of reptiles took on the role of apex predators on land, and

by 240 million years ago, a group of archosaurs, the rauisuchids, appear in the fossil record.

Meanwhile, with these predators running around, another line of plant-eating archosaurs, the

aetosaurs, came to be covered in bony armor.

And another lineage became adapted for catching fish.

These reptiles, called phytosaurs, developed long, narrow snouts lined with teeth in just

a few million years, thanks in part to the lack of competition for the role of river-dwelling

fish-eaters.

But, you know what happens next!

Starting around 201 million years ago, a wave of volcanic activity, along with

Pangae's break up, released tons of CO2 into the atmosphere, causing rapid global warming and

ocean acidification.

It brought an end to the Triassic Period -- and also the end of about three quarters of the

world’s species, including the aetosaurs, phytosaurs, and the drepanosaurs.

This time, it was the dinosaurs who were the big winners, because they were small and unspecialized,

which may have helped them survive.

And then they went on to fill the empty ecological niches that were once filled by Triassic animals,

setting off a whole new round of adaptive radiation.

The aetosaurs, for example, were gone, but stegosaurs and ankylosaurs eventually took

their place as armor-covered herbivores.

Likewise, with the disappearance of the phytosaurs, spinosaurids and crocodiles were able to move

in to dominate as freshwater predators.

In fact, most dinosaur groups replaced earlier species that had filled a similar niche.

And they often wound up repeating some of their body plans, too -- a classic example

of convergent evolution, where similar selective pressures can lead to similar physical results.

And this whole cycle has repeated itself throughout history -- extinctions strike, only to be

followed by bursts of evolutionary innovation through adaptive radiation.

In fact, after the non-avian dinosaurs were wiped out, the surviving mammals and birds

went through the same rapid burst of evolutionary change, filling the niches left empty by the

dinosaurs.

Even though the history of life is marked by devastating mass extinctions, the survivors

rally each time, with adaptive radiations produce a dizzying number of new species,

and body plans keep showing up, molded as they are by the same selective pressures.

It’s a pattern that will go on probably forever -- including after the next mass extinction.

As some guy once said,

life finds a way.

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