climate change in the middle Cretaceous , they were the ones that then had the opportunity to take over in the late Cretaceous . But still, again, this is largely a mystery. By the latest Cretaceous , and I'm talking between about 80 million years ago and about 66 million years ago, by that time, the continents had moved around so much that Pangaea was a distant memory, and a mapof the world would have looked pretty similar to the world today. There were small differences, sea level was much higher, there were no ice caps at the poles. India was an island in the middle of
were the ones that were being very good at being small. Now, during the Cretaceous period, there was this burst of evolution, not just of mammals, but of lots of other species, that we call the Cretaceous terrestrial revolution. It's a bit of a bombastic term, maybe. But in many ways, it was revolutionary because it touched so many aspects of life and of food webs and of ecosystems. Andwhat really triggered it, it seems, was the rise of flowers. So in the world today, flowers are all
it is one of the most incredible stories of evolution. We wouldn't know about it if we didn't have the genetics and the fossils together to tell us that story. After the asteroid hit, the Cretaceous turned into the Paleocene, the age of dinosaurs, gateway to the age of mammals. But really, this greenhouse world of the dinosaurs persisted. The Earth was still very warm. There were no ice caps at the poles, for instance. Then the Earth got even warmer as the Paleocene turned into the Eocene with this spurt of global warming. It got so hot that there were crocodiles lounging
The glaciers grew into ice sheets. And that helped drive the temperature of the entire world to be much cooler. Now, this was a long-term trend then that continued to happen for many tens of millions no Cretaceous cassette tape that we can find in the fossil record and plug in, and hear what these things were sounding like. But sometimes we do get clues from the fossils themselves. And in
because the fossil record largely goes silent. We know things are changing because we can see that in the early Cretaceous , there are certain groups of dinosaurs that are dominant and diverse. You have things like the Spinosaurus with the scales on their backs and the long snouts that ate fish and swam around in the shallow water. You had big Carcharodontosaurus predators.
small, while they were still the size of humans and horses, it was then that they were developing these larger brains and keener senses. So it seems that being smart may have helped Tyrannosaurs endure this middle-cretaceous extinction. Now, how did hunt though? That's a question that a lot of paleontologists have wrestled with. And these are difficult questions to answer, frankly. But there is some evidence that Tyrannosaurs were pack hunters. And that is different than how they're often depicted in films as these solitary murderers. Now, the evidence
of these flowering plants. So that humble, what seems like a very humble origin of a flower, it triggered something groundbreaking and something revolutionary. And mammals in particular really blossom during the Cretaceous -Terrestrial revolution. And a lot of the modern groups of mammals, it's not that they quite got their start then, but their immediate ancestors got their start during the Cretaceous -Terrestrial revolution. And one of the key things is that there were all these mammals that were eating bugs, eating fruits and eating flowers. And
blossom during the Cretaceous -Terrestrial revolution. And a lot of the modern groups of mammals, it's not that they quite got their start then, but their immediate ancestors got their start during the Cretaceous -Terrestrial revolution. And one of the key things is that there were all these mammals that were eating bugs, eating fruits and eating flowers. And that is involved in the evolution of a new type of tooth, a new type of molar tooth, the type of molar teeth that we have that can both shear food and crush food. These are very distinctive teeth,
The glaciers grew into ice sheets. And that helped drive the temperature of the entire world to be much cooler. Now, this was a long-term trend then that continued to happen for many tens of millions living in the Cretaceous period. So by the end of the Cretaceous , you would have had some birds that could sound like the birds of today. But it is really just one clue. We need to learn so
So we live on the front range, and just to the east of the front range is a pile of rocks that contain the Cretaceous Tertiary, or the Cretaceous Paleogene boundary. And so this site here, this is Corral Bluffs, just outside of Colorado Springs.
This is also the most famous mass extinction. This is the end Cretaceous . This event took out, most famously, the non-bird dinosaurs.
So here's the twist. At the end Cretaceous , not only is there a gigantic asteroid impact, the biggest that we know of in the last billion years, there's also one of the biggest volcanic events in the history of animal life.
And so, for me also-- I mean, I've been married for a certain number of years, going up on 20 years now. I'm Cretaceous period. You know?
You have things like the Spinosaurus with the scales on their backs and the long snouts that ate fish and swam around in the shallow water. You had big Carcharodontosaurus predators. Then later on in the Cretaceous , they're gone, are mostly gone, and you have Tyrannosaurs and other major groups. But best we can tell from the rocks that we have and the fossils that we have, and especially the clues of the chemistry of the rocks, which can tell us a lot about temperature and precipitation and sea level in climate. It seems like there was a period of climate change,
a period again of global warming, a period where sea levels were moving around. And out of that came new types of dinosaurs. And the dinosaurs that were able to survive, that interval of climate change in the middle Cretaceous , they were the ones that then had the opportunity to take over in the late Cretaceous . But still, again, this is largely a mystery. By the latest Cretaceous , and I'm talking between about 80 million years ago and about 66 million years ago, by that time, the continents had moved around so much that Pangaea was a distant memory, and a map
got a little bit bigger. Some of them got to be about the size of horses. A few random species here and there kind of supersize themselves in their own local environment. But by and large, they remained small predators until this middle Cretaceous turnover in dinosaurs. This time of climate change that we don't know much about. But we know that it wiped away many of the incumbent top predators, the spinosaurus and the allosaurs and the carcardana. So with those animals out of the picture, now a job was open at the top of the food chain. And in North America and in Asia,
The glaciers grew into ice sheets. And that helped drive the temperature of the entire world to be much cooler. Now, this was a long-term trend then that continued to happen for many tens of millions an animal at the end of the Cretaceous and you ate parts of a growing plant, leaves, flowers, fruits, roots, your food would run out really quickly. But if you could eat seeds, that would be your ticket
And then what really blows my mind is that they faced extinction at the same time. At the end of the Cretaceous when an asteroid smashed into the planet and all of the non-avian dinosaurs went extinct, so did most of the cephalopods. It was a very bad day.
They had these really weird-- they're called heteromorphs, but we won't get into that. So that's the end Cretaceous . People are pretty familiar with that, they know about dinosaurs, they know an asteroid hit.
There's no land, basically, in the northern hemisphere, and Africa's over the South Pole. So at the end of the Cretaceous , people think, oh, the mammals thrived and the dinosaurs went extinct.
which dinosaurs were firmly in control, even though it wouldn't last a whole lot longer. If you woke up on the last day of the Cretaceous period 66 million years ago, you would have woken up to a world thrown into turmoil. This was an asteroid, and not just any asteroid, the biggest asteroid that was sniffing around our part of the solar system over the last 500 million years. It was about six miles wide, about 10 kilometers wide or so, so a pretty sizable rock, and it smashed into
it deserves all the accolades that it gets. That, of course, is T. Rex, the tyrant lizard king, the king of the dinosaurs. And it was the top predator in North America at the very last stage of the dinosaurs at the end of the Cretaceous . But it wasn't always that way. T. Rex came from a long line of ancestors. Ancestors that changed and adapted and endured and survived. And believe it or not, the fossils show that the Tyrannosaur family goes back more than 100 million years before T. Rex. T. Rex was the crowning achievement of a long period of evolution. And for most of
And all the bite marks are on one bone, the humerus, the upper arm bone. - Yeah. - from the early Cretaceous period, about 112 million years ago, found in what is now Alberta, Canada. Amazing.
And you can notice that there's a couple of pretty big jumps right here. The largest mammal that's in the latest Cretaceous is about the size of a raccoon. The largest mammal to survive the mass extinction is about the size of a rat.
In 1980, Walter Alvarez and his dad, Louis Alvarez, at UC Berkeley, essentially discovered a layer of asteroid dust in the layers between the end of the Cretaceous , right when big dinosaurs go out, and then the Age of Mammals. And then in the early '90s, paleontologists linked this to 110 mile crater in the Yucatan Peninsula in Mexico.
252 million years ago was the end Permian, which is the biggest mass extinction of all time. So interestingly, the end Cretaceous , we think of this big horrible thing. But it wasn't even remotely close to the worst mass extinction of all time.
And again, anytime there's a dive, there's a mass extinction. The most recent one, the end Cretaceous extinction of course is responsible for the extinction of the dinosaurs. But I want you to think about extinctions a little bit and what they mean, what they mean for the course of life.
where the cotton fiber was turned using the machines into the textiles, which were then taken back down to Africa. milliom-year-old rocks, this Cretaceous region, still has the highest density of African-Americans living there-- people that, unfortunately, are still afflicted with socioeconomic problems,
And then there's end Ordovician mass extinction, 445 million years ago. So armed with the knowledge that an asteroid hit at the end Cretaceous , and this story really coming together in the '90s, geologists and paleontologists went back to these earlier events trying to find a record of impacts at the other mass extinctions.
It's almost as big as the asteroid impact that killed the dinosaurs. And so this was originally thought to be the culprit of the end Cretaceous -- or the end Triassic, 201 million years ago. And when geologists dated it, they were shocked to find it was 14 million years too early, in a time where basically nothing was going extinct.
middle of the mountains. Even the roads leading here have had to be carved out of the hills. It's the biggest thing to happen to the Western Ghats since the cretaceous period." So you can imagine how weird it was for me to turn up, to drive for two hours in the night and then turn up in the middle of a hill and be eating omelets in an American diner with pitch black all around me and nobody there because the workers had
time frame. But you have dinosaurs continuing to adapt and evolve as the continents move around. Now, where we really start to see a change is a little bit later in the Cretaceous , in the middle part of the Cretaceous . But here things get a little bit frustrating again, because the fossil record largely goes silent. We know things are changing because we can see
general little afterthoughts of Earth history. No, that's not the case at all. And with fossils, we see this. Now for a long time, there were not a lot of good fossils of the mammals of the Triassic, Jurassic, and Cretaceous living with dinosaurs. These were small animals. It's true. And because they were small, it was hard to turn them into fossils. So for a long time, it was only a few little jaw bones, a bunch of isolated teeth. And that's all that we really knew. We had to
The glaciers grew into ice sheets. And that helped drive the temperature of the entire world to be much cooler. Now, this was a long-term trend then that continued to happen for many tens of millions cards at this crazy, maniacal poker table at the end of the Cretaceous . And I think it is a really,
The glaciers grew into ice sheets. And that helped drive the temperature of the entire world to be much cooler. Now, this was a long-term trend then that continued to happen for many tens of millions really interesting question because it gets at, would the Cretaceous world of T-Rex, let's say, what would that soundscape have been like? Would it have been like the modern world, or would it
It's the origin of the modern world. It's such an incredibly important interval of time that scientists have been going to these areas around the world that preserve the Cretaceous Paleogene boundary to try to squeeze every bit of data from these rocks, to try to figure out how the world originated.
And unfortunately, it's notorious for having a really poor fossil record. I've been working in the this, right after the Cretaceous Paleogene boundary, for about 20 to 25 years, and I can count on one hand how many mammal fossils, mammal jaws I've found prior to this major discovery.
You're looking at things, well, you see a scale bar there for 50 microns up there on the top. And this little diagram in particular is showing you the change in plant life across what is called the Cretaceous Paleogene boundary. So the bottom being a diverse assemblage of different kinds of pollen types, those pollen types representing a forest, a very diverse forests.
They were a major part of the ocean ecosystem. Interestingly, there weren't coiled at the end of the Cretaceous . They had these really weird-- they're called heteromorphs, but we won't get into that.
Trees are starting to take over the planet, which might be really bad. So actually, I'll go back to the end Cretaceous . There's been this really interesting story going on the last few years.
And number five, that's the most famous, most popular, if you will. And that is the extinction event that did in the dinosaurs and a lot of other groups at the end of the Cretaceous Period. And there's a pretty broad scientific consensus that that was caused by an asteroid impact.
living in the American West. And today, we find their fossils in places like Colorado and Wyoming and Montana, Utah and the Dakotas. These are some of the richest fossil sites in the world and its Jurassic dinosaurs. That we can find there. About 103 million years ago, the Jurassic transitions into the Cretaceous . And unlike many of the other transitions in Earth history, between one period and another, this one is not marked by some great extinction or some spasm of volcanism or the impact of an asteroid. It really is just a line geologist used to divide a long
the ocean racing northwards to collide with Asia, but by and large, if you looked at that map, it would look similar to us. And on those different land masses lived different dinosaurs. The ones in North America were quite distinct from the ones in South America and the ones in Africa. And where we really see that is with the top predators, the latest Cretaceous , this was the kingdom of T-Rex, but only in North America. There were other close Tyrannosaur relatives at the top of the food chain in Asia, but south of the equator in South America, in Africa, it was totally different
of reptiles that could fly, but they were not dinosaurs. They were the biggest predators in many parts of Europe and it's all because of the geography, because different continents, different land masses had different climate, different weather patterns, different environments, and that bred this richness of dinosaur diversity. And it really does seem that in the latest Cretaceous , this was the apex of dinosaur diversity, the time when they were thriving most, when there were most species, the largest number of species, different species living in different places, a world in
But these are the mammals that give birth to tiny little babies that are born very premature, that then develop more further in their mother's pouch. So these are the three major types of mammals. Placental mammals are the dominant ones today. But we see the roots of these three major groups back in the Cretaceous period. Now what we see in the fossil record is that those features didn't just evolve in one burst. They evolved one by one over time in many ancestors.
is we never find a fossil of a T-rex the size of a mouse, a triceratops the size of a shrewd. Mammals were the ones that were being very good at being small. Now, during the Cretaceous period, there was this burst of evolution, not just of mammals, but of lots of other species, that we call the Cretaceous terrestrial revolution. It's a bit of a bombastic term, maybe. But in many ways, it was revolutionary because it touched so many aspects of life and of food webs and of ecosystems. And
the plants in our parks, most of them have fruits and flowers, and they have beautiful fragrance smells. A huge percentage of the plants today are flowering plants. But flowering plants are a very new innovation in the history of life. The oldest fossils of plants with flowers are from the Cretaceous . So for the first, you know, four billion plus years of Earth history, no plants with flowers. Now, when flowering plants entered the scene, they diversified, they adapted. Some of them became big, became trees. We have palm and magnolia trees in the Cretaceous
very intricate teeth. You look at a tooth of a shark or a crocodile or a T-Rex, yeah, they might be plenty scary looking, but they're pretty simple, steak knives. But our teeth, no, all the ridges, the valleys, the depressions, the way they interlock with each other, that's the classic mammal molar, and that evolved during this time of the Cretaceous -Terrestrial revolution as all these new food sources, insects and flowers and fruits and so on were there to be enjoyed.
The glaciers grew into ice sheets. And that helped drive the temperature of the entire world to be much cooler. Now, this was a long-term trend then that continued to happen for many tens of millions as a gorilla. They were the top predators in the southern oceans after the ocean reptiles went extinct with the dinosaurs at the end of the Cretaceous . Later on they were superseded
The glaciers grew into ice sheets. And that helped drive the temperature of the entire world to be much cooler. Now, this was a long-term trend then that continued to happen for many tens of millions of that ancestor had to traverse and endure so many tribulations. They had to do the same thing our mammal ancestors did and that is survive the asteroid that ended the Cretaceous and killed 75%