A Brief History of Life: Dinosaur Time!

Welcome to the third installment of our miniseries
on the history of life on Earth! When we left off, life had been brought to
its knees by a mass extinction at the end of the Paleozoic era. 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. Including the dinosaurs! 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, pretty much disappeared. 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 supercontinent Pangea. Slowly, life started to repopulate the place. Repopulating meant diversifying. The therapsids were declining, but a new group
of vertebrates was starting to take over — the archosaurs. Archosaurs descended from one of the earliest
major groups of land vertebrates, the diapsids, at the end of the Paleozoic. 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 very clear marker: 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 and alligators. 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 time as dinosaurs. Yes — we mammals started out as dinosaur
buddies, and we still hang out with dinosaurs now, just in bird form. 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, but it’s definitely close. 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 and their immediate ancestors. But somewhere between Nyasasaurus and later
dinosaurs like Eoraptor, they had officially evolved, ready to take over the world. 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 evolving a land-based lifestyle. They’re also one of only two groups to evolve
a fish-shaped body from a four-footed animal body. The other group being the whales. 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 and Gondwana. Shallow seas covered parts of the land. 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 that walked on four legs. 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 as well make it awesome. Meanwhile, the Plesiosaurs, a group of reptiles
not closely related to dinosaurs, joined ichthyosaurs in the oceans. 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: that’s a weird experience. That’s a whole, strange thing. Archaeopteryx, which is usually considered
the earliest bird, dates back to the Jurassic, and so do lots of other early birds. They, along with the pterosaurs, were the
two kinds of flying archosaurs during the Jurassic — and during the next period, the
Cretaceous. The Cretaceous, which means chalk-bearing,
lasted from 146 to 65 million years ago and was even warmer than the earlier Mesozoic. The continents continued to drift apart, heading
for where they are now. As the seafloor spread, it released carbon
trapped in the Earth’s crust and caused some serious global warming. Ichthyosaurs disappeared sometime during the
Cretaceous. But a new type of marine reptile appeared:
the mosasaurs, aquatic lizards related to the monitor lizards we have today — but not
closely related to dinosaurs. Another new arrival? Flowering plants, which were excellent at
getting animals to spread their pollen. That’s why, at the same time as flowers,
we see pollinators like bees appearing in the fossil record. Whether flowers or pollinators came first
is a kind of evolutionary chicken-and-egg question. Probably neither one of them came first, exactly. The flowers and pollinators influenced each
other’s evolution and became more interdependent as time went on. Mammals — which, you’ll remember, had been
around since the Triassic — evolved into the major lineages alive today: placental
mammals like us, marsupials like the opossum, and monotremes like the platypus. The Cretaceous also meant even more dinosaurs! Like the frilled ceratopsians, the duck-billed
hadrosaurs… …and, of course, Tyrannosaurus rex. I don’t know about you, but I think T. rex
is pretty cool. I’m also very glad predators that size aren’t
around today to snack on us. Why aren’t they around any more? Like the Paleozoic, the Mesozoic ended in
a mass extinction. But there were a few differences between the
two die-outs. For one thing, the extinction at the end of
the Mesozoic wasn’t as bad. Only about 50% of Earth’s species went extinct,
which is a lot, but not nearly as many as during the extinction at the end of the Paleozoic,
when almost all life died out. And while we don’t know exactly what caused
the earlier Paleozoic extinction, we have a major clue about the event at the end of
the Mesozoic. It’s a crater in the Yucatan region of Mexico. Most scientists agree that a meteor impact
at this site must have been what wiped out all of the dinosaurs except for birds. There might have been other factors at play,
but the meteor didn’t help. So most of the diversity dinosaurs had to
offer is gone for good. Sure, birds are cool, but they only represent
one lineage of dinosaurs. Those big four-footed plant eaters and the
walking around armored vehicles? They’re not around anymore. But once they were gone, mammals had a chance
to take over — which is what happened during the Cenozoic, the era that we are still in,
which we will talk about next time. Thanks for watching this episode of SciShow,
which was brought to you by our President of Space, Morgan, and The Big Try Hard. Morgan just completed a bicycle trip across
the U.S. raising money for YouTube channels he loves. Thank you, Morgan! You can catch up on his journey at thebigtryhard.com
and if you want to help support this show, just go to patreon.com/scishow. And don’t forget to go to youtube.com/scishow
and subscribe!

Comments 100

  • "Chicken nugget shaped like a dinosaur"
    -What the hell, America?

  • Thanks for this series, it's great!

  • Your sound is a bit echo-y this episode. But yay! Dinos. 🙂

  • 4:41 Yes! Thank you! Thank you for pointing it out! Finally! I can be relieved of my fear that people think Tyrannosaurus was from the Jurassic!!

  • For a Tyrannosaurus rex, a Stegosaurus was as old as the T. rex is to us 😀

  • "early birds"! I see what you did there…

  • What if the dinos died because all of the plants were eaten, and then they starved and died and then carnovoirs ate them then no meat left and deeeed.

  • Crocodiles running on two legs sounds horrifying.

  • great job. keep it up please. I hope someday you do a even more in-depth version s.

  • interesting vid. Good work!


  • you guys know what this means right? The national animal of the united states, IS A FUCKING DINOSAUR!!

  • Another strange thing. Plastic is made from oil and oil is made from ancient dinosaurs. So plastic dinosaur toys are made of dinosaurs. (i know plants made most of the oil but still)

  • Incorrect k-t mass extinction wiped out 75% of all life on earth including all the pleiseosaur correct me on spelling 90% of crocodiles all mosasaurs all non aivian dinosaurs and pterosaurs

  • so will the cenezoic end when theres another mass extinction? the next one imo would probably be from nuclear fallout


  • i wonder if some other species is going to be making videos about us and our time.

    140m years ago, or acestors, the humans lived…

  • 5:31 xD lol

  • I am a nerdfighter that works as a park interpreter in Dinosaur Provincial Park in Alberta, Canada. I teach people about cretaceous-era dinosaurs every day. This video is awesome. Thank you so much.

  • Hank is such a weirdo, never smoked. Doesn't like spiders.
    And now… who honestly doesn't want to get chased by a T-Rex?

  • Royal Terrell museum, Drumheller Alberta Canada, sells dinosaur shaped chicken nuggets. I had some when I was really young and they were delicious

  • Why is Gondwana referred to as 1 continent when on every map i've ever seen, it's clearly broken into 2 land masses. Present South America and Africa are completey seperate from India

  • Serious question: is it called the Thagomizer because of Gary Larson and The Far Side? Or did Gary Larson use the fact that it's called a Thagomizer to make a humorous comic?

  • So my cats eat dinosaurs. Awesome

  • quick note: the name Thagomizer comes from a farside comic

  • I was doing some dinosaur youtube browsing and I came across this video that showed that you can get 'soft' tissue from dinosaur bones as well as traces of carbon 14, which i guess there should be none of. they wanted to date dinosaurs with ancient Egyptians, which is probably not legit, but the carbon thing was kinda interesting. could you guys do a video on that issue specifically?

  • I thought I heard somewhere that when chickens are still being incubated in their eggs they actually have a tail growing that looks like a dinosaurs. But as it develops this comes off. Does anyone have information on this? the reason why I mention it is because I guess it would only further prove that birds are descendants of dinosaurs.

  • When hank says that most of the Jurassic Park's dinos aren't even from the Jurassic and some are even made up, i feel the strange urge to ask ''What do you mean santa doesn't exist?!''.

  • I'd heard all of it right up until the crocodile nightmare fuel, and then I really wanted to nope the fuck out.

  • Early bird pun +1

  • "The Thagomizer" is named after the late Thag Simmons. It's not the only Far Side reference to have made it into academia.

  • Hank is glad predators that size don't exist today? One word: Orcas.

  • Dinosaurs were just proto-birds.

  • When it comes to mass extinctions, the question in my mind has always been whether they were losses of bioDIVERSITY or losses of bioMASS. It's tricky to tell the two apart in the fossil record; we don't have a good sense of how many of any one thing was alive back then, since fossils aren't preserved in the same ratios as you find in a biosphere. We have very few worm fossils, for example, but a whole lot of clams, yet worms make up as much or more of the biomass in any ecosystem. In the end I agree that after the Permo-Triassic mass extinction there was a lot of colonization by various groups, but I'm not sure how far to take that. The question is, how many swaths of the planet were truly barren? The answer is, we don't know and probably never will.

    In terms of identifying things based on their skulls, it's not the ONLY way the synapsids/diapsids are differentiated (there are post-cranial skeletal differences), but it's a major way. Mammologists take this to the extreme. I've often wondered what it would take to write a book on the post-cranial osteology of Mammalia. The issue is that while most bones preserved are post-cranial (meaning from the neck down), the most easily identifiable remains in any vertebrate are the skulls. And most taxonomists have historically plucked the low-hanging fruit. I'm not saying the video is wrong–this IS the major way of differentiating those groups–I'm just adding that there's a nuance here that goes beyond the bones. A lot of this is due to psychology of the researchers, not necessarily due to the bones themselves.

    I'm uncomfortable with saying that dinosaurs had an advantage….The issue is, we call it an advantage because they won. If the other groups around at the time had won, we'd look at their anatomy and say "Well of course they won, look at features X, Y, and Z." It's really easy to pick the winner of a horse race after the race is over, and see why they won. The trick is picking the winner BEFORE the race. There's a lot of randomness (Gould called it "contingency") in the history of life, and particularly in mass extinctions.

    Crocodilians are one of the groups I think is WOEFULLY under-represented in pop culture. There's a creature in the Elder Scrolls videogames called a daedroth–a bipedal crocodile, basically. Those are fairly terrifying the first time you encounter one in the games (particularly Oblivion, with its broken leveling system). The terrifying thing is that real crocodilians would have made the daedroth look like a fluffy little kitten. We're talking huge creatures, vicious carnivores that successfully competed with the biggest dinosaur predators. We're talking predators that could run as fast as the faster big cats today. We're talking creatures out of nightmares. I love that kind of thing! 😀

    The issue with identifying the original ancestor of a clade is a fun one, and one that will, if you find yourself at a conference with a bunch of cladists/taxonomists, provide ample opportunities to talk to both the most knowledgeable folks in the conference and the best-looking members of either sex. It boils down to this: The first member of any clade, by definition, looks more similar to things NOT in the clade than most ancestors IN the calde. The reason is that the original ancestor of any clade is part of another clade, and has related species in that other clade (which, incidentally, the new clade is part of). It's easier to show with cladograms, but that's the reality. And the math we use to establish cladograms has a lot of trouble with that. It groups things according to similarity (that's VASTLY oversimplifying, and anyone interested can download PAST for free and look at its literature).

    Speaking of this: You touch on it, but yes, strictly speaking a clade is any species and ALL its ancestors. You can also have polyphyletic groups, meaning a "group" composed of members of multiple clades–for example, lizards. These are not considered real in biology. Paraphyletic groups (para=cut) are those that include a species and SOME of its ancestors. These…..are complicated. Strictly speaking, they're wrong and bad and we shouldn't use them. But that gets you into trouble. Strictly speaking, if there's a species A, and species B evolves from A, the name for A now refers to the group A+B. You can literally be forced to name a new species despite there being NO change in that species. Taxonomists wisely opt to say that's stupid, because it is, but that's a legitimate interpretation of the principle. More problematically, you can sometimes have a single group branch off a clade and become so different that it makes sense to talk about it separately. Birds are a great example of this. There's a clear demarcation between birds and non-avian dinosaurs after the K/Pg mass extinction–birds lived, the rest didn't. So while evolutionarily they are dinosaurs, it makes ECOLOGICAL sense to refer to all non-avian dinosaurs as "dinosaurs" and birds as "birds". This is actually really common in paleontology. The issues get a lot more complicated; I'm just trying to give the 1:5,000,000 scale overview!

    The thagomizer (one of my favorite pieces of dinosaur anatomy) got its name from the Far Side comic. Paleontologists are giant nerds, so literally none of us saw anything wrong with doing so. 😀

    I'm VERY hesitant to give numbers or percents of species that went extinct in a mass extinction. What actually happens is that we evaluate the number of some higher-order taxa that went extinct (families or orders), and estimate the average number of species in that higher-order taxa (say, 10 species per family, plus or minus six), then run the math. It's a guestimate. And I'm very dubious about the methodology, for a host of reasons.

    Thank you for putting the blame for the K/Pg mass extinction squarely where it belongs–on the bolide impact!!! This was honestly one reason I avoided this video for a while. Too many people fall for the nonsense about a gradual extinction. There's a lot of reasons why a sudden extinction would look gradual in the rock record, though, and no reason why other things going on at hte time could have caused it. Gerta Keller and her students are the primary hold-out for the sensu stricto Uniformitarian interpretation as a slow, gradual extinction; the rest of paleontology has accepted the Alvarez Hypothesis at this point.

    I'm….torn about the Cenozoic. I'm very, very tempted to agree with some researchers that we've entered a new era, the Anthropozoic. Time will tell, I guess, and it's one of the sad parts of being a paleontologist that I can see this wonderful question playing out, but know that my lifespan will be too short to see the ultimate conclusion. By the time we finally know for sure, I'll have joined the dinosaurs in the fossil record. Grim, but beautiful none the less.

    All in all, this episode was far too brief for my taste, but then I'm a dinosaur guy when it comes right down to it. I'd be perfectly happy if every video on YouTube was about dinosaurs and the creatures that shared their world! I wish you'd have covered things like the Ocean Anoxic Events and a few other issues life encountered during this era, but this is a very good overview of a very weird and wonderful phase in evolutionary history!

  • 5:53 I am dying!!!! XD

  • arent all dinosaur bones displayed in museums artistic speculations

  • if the great dying never happened the sea animals would have evolved to be intelligent

  • All of evolution, all the amazing things nature has done, all the hardships my ancestors had to endure, and all the evolutionary breakthroughs they had undergone, resulted in me writing this comment, while sitting in my bed, eating KFC.

    Good job evolution.
    Good fucking job. (quite… literally.)

  • I am going to pick up a bone fragment or maybe more than that and then tell you the details of what happened to that creature hundreds of millions of years ago. Come'on people, this stuff is wacky science. I am not saying I know what happened hundreds of millions of years ago but I believe it is poor use of reasoning to believe people who say they know what happened hundreds of millions of years ago. Think about how hard it is to decipher history from only a few thousand years ago, and that's with a a bit of recorded history to help out, and still it's hard to know exactly what happened. Yet these wacky dinosaur pseudo intellectuals love to force their Dino delusions on everyone. Everything they spew is a theory. A theory is just what some dude's thinks happened. The dude who lives next door to me thinks robots terra-formed the planet, that's his theory, I mean that's what he thinks. What do you think? Your theory about what happened hundreds of millions of years ago has the same amount of legitimacy as anyone else, including these Cult of Dino Delusionalists.

  • Many glaring errors.

  • I was never especially interested in dinosaurs (no more than anyone else, at least), and maybe that's why this episode is so fascinating to me.

  • Cooooooooooooooooooooo

  • Probably because the birds were flying at the time.

  • B-b-b-b-but gad crated teh wurld n univarz 🙁

  • "Thagomizer" is not just a "cool" name to call something, it comes from Gary Larsen's "The Far Side" comic strip. In one of the strips while instructing others a caveman points to a depiction of a Stegosaurus. Indicating the tail he says, "This is the thagomizer, named after the late Thag Simmons." Thus the name was born and it got adopted into reality.

  • I love these videos.

  • but does the Archaeopteryx get the worm?

  • you guys are teaching me alot

  • So, Crocodiles and Alligators AREN'T dinosaurs??



  • I hear eoraptor I think egoraptor.

  • So if birds are dinosaurs, does that mean mammals are reptiles? Considering that all mammals are descended from reptiles?

  • Dinosaur time is my favorite time of day.

  • Eoraptor sounds like a band name.

  • i come here just for the chicken nugget joke

  • did I just listen to a folk tale from science channel?

  • Wait, so it sounds like the crocodiles and alligators are descended from animals that had straight, under-body legs. Yet crocodiles and alligators are splay-legged reptiles. That's kinda weird if they "regressed" to be less efficient at traveling over land.

  • 7:17 there is recent evidence which proofs that Mammals were already quite sophisticated during the time of the Dinosaurs.

  • Actually around 85% of all life on Earth died out at the end of the Mesozoic.

  • you forgot about Velociraptor

  • In the Jurassic franchise the dinosaurs did exist (except Indominus rex). They had the names right, but the physical components were wrong.

  • Nice 'update' on dinosaurs—long time coming–but some of the implications are strange, like the Cryolophosaurus ellioti of Antarctica 192 Mya either evolved in 7 Myr meanwhile everything else took 15-20 Myr (what did it eat before waiters existed), else it preexisted, that global extinction of 199 Mya, that maybe wasn't, global, but evolved from whence….

  • 6:40 I know those things, they are basically like a Komodo Dragon, cross bred with a sea snake, except they grew to over 60 feet in length, and weighed around 8 tonnes at max, and they basically took over the entire ocean, they were the Apex Predators of the Cretaceous oceans

  • Wow, dinosaurs are delicious.

  • dinosaur!

  • 4:03 I seriously thought he said Egoraptor

  • This guy sound kinda like Daffy Duck

  • I'm still confused. So if all the descendants are classed under the same name, why do we call dinosaurs "dinosaurs" and not "archosaurs" so the pterasaurs can be part of the cool club again? And why do we call mammals "mammals" and not "therapsids"?

  • I think T Rex gets way too much of the credit when it comes to dinosaurs

  • you said only cetaceans and ichthyosaurs are the only two 4 legged animals to fully evolve to the water.
    how about sirenia (mantatees) there related to hyraxes and elephants

  • Excellent series!

  • "The meteor didn't help"

  • I wish we could have a series that covers every era specifically

  • i want to say a most of the gentics where off

  • You said "early birds" but didnt metion getting the worm….

  • is it just me or is hank's lisp really bad in this clip. so cute.

  • l wouldn't bother reading anymore. It's just a bunch of religious nuts sprouting rubbish at each other. So over it

  • I wonder if mammals survived because they were already adapted to a life underground, with poor oxygenation. Maybe when CO2 levels rose, mammals were forced to come to the surface for air, which usually would have made them and easy snack, but conveniently found that all the dino's had chocked to death.

  • So when you feed your child a dinosaur shaped chicken nugget you're basically feeding your kid the meat of a dinosaur that's in the shape of a dinosaur

  • How big was the worm for the “early bird”?

  • Why didn't birds die out at the end of the Mesozoic?

  • i love how he shows the sources <3

  • My African Grey is named Nyassa. My wife and I thought, "yep, he's a dinosaur."

  • I thought the T. rex wasn't a predictor I thought they where like leaf eaters

  • Ok I turn 15 in march and lemme tell you, dino nuggets are the best nuggets

  • You talked about the first bird, what's the last one to evolve?

  • pokemon names are great bc when you randomly find out what they mean its like Ah ha. loke archeopteryx is arceops

  • Dinasors didn’t evolve in to birds

  • How do you explain how that evolve ya that’s right THAY DIDNT

  • Ladies and Gentlemen, I registered your channel, can you subscribe to my channel?

  • **Dinosaur shaped chicken nugget**

  • I am really surprised that koolasucas looks like a arcisoaur but a bit diffr2nt

  • Which came first;? The chicken or the egg? Well according to the bible. Neither it was the roaster! God.jesus. The holy spirit all males!

  • Good explanation and I want to show it to my young learners but why does so much of footage have to be centered on the guy talking. Show me more charts and pictures to keep my kids interested.

  • So the archaeopteryx's diet was worms right? I mean, it's the early bird.

  • Wayw

  • The big TriHard 7

  • What a strange belief system based on tons and tons of fossils but there is none missing link fossil to be found. People would do anything just to ease their minds and think there is no God, just to do whatever they want without responibility in the end.

  • How bout the power of flight. That do anything for ya? It's levitation homes.

  • Jesus Christ on a crutch, descended from Jesus Christ himself.

Leave a Reply

Your email address will not be published. Required fields are marked *