[SOUND] [MUSIC] The earth now is ready for the onset of the mammals. And the mammals required the KT impact To do away with the, diapsid reptiles, that were, the conquering kings and queens of the rest of the Earth ecosystem. So, now that we've gotten to the point that the meteor impact has decisively removed our competitors, the mammals, the synapse of reptile lineages are ready now, to emerge and take over the planet. Now we know that mammals are part of a very diverse and amazing suite of organisms. But until we look closely at what's happened in the Cenozoic post-KT impact, we really don't have any idea, truly diverse magnificent the mammals are. So what we want to is consider a bit of overview of what was happening in this time period as we move away from the KT impact of 65.5 million years before present then into the Cenozoic itself. Now, one of the first organisms that did very well after the K/T impact and the demise of the dinosaurs were actually the birds. And some of those birds evolved from carnivores therapsid saurischian dinosaurs. And that evolution from Archaeopteryx into the birds is well documented. [COUGH] But then at the KT impact, what we saw were the large land based birds rose and really dominated the ecosystem. So in the time period of the Eocene as an example, we had these two to three meter tall killer birds. Very large legs as you see in this image. The large beaks. And so these are big predators that were around. And they did fill the ecospace and do fairly well. But eventually they were completely out competed by this emerging and very diverse group of mammals that were appearing on the planet. So we need to remember that at the KT impact the types of mammals that survived were not the big mammals with all the teeth and all the different attributes that we want to start thinking about in terms of mammalian evolution, but they were tiny squirrel or mouse like organisms so in the Eocene, is a good example. They look like mice or squirrels, with longish ears, and long tails. And, all the mammals virtually, that made it through the KT impact, were of this size. And so, it turned out that even though the KT impact was a devastating event for most things that were living. The small body size of these mammals allow them to access an ecosystem space, let's say down below in burrows and the foliage and things that were living down on the floor of the forest at the time. Once the meteor impact shut off photosynthesis and all those trees and plants died for prolonged period of time they were still living in these small ecospaces where they could still eke out a living and make it through the impact devastation. So another hallmark of the mammalian revolution st this time in the early Cenozoic is the marine environment. And we saw that a lot of the mammals that had thrived in the terrestrial environment actually moved back into the ocean and we'll be considering some of these as we move forward. And large predatory whales of scales that we can barely imagine. And these predatory whales, these carnivorous whales were alpha predators at that time period in the world's oceans. But let's now think carefully just about what are some of the hallmarks of what we see, and one of them is that we saw primates arise in this time period, and the primates then move rapidly then on an evolutionary trajectory towards the hominid and human evolution. So that's kind of one of the pathways and lineages that we'll be considering. But at that same time period, the mammals were evolving in the terrestrial realm to access the different types of, especially plants that were available to eat. And so once you start having the, as we saw in the Diapsid reptiles, and their evolution in the Mesozoic. Once you start opening up these ecosystems that have these food sources for the herbivores, then you quickly respond by having some very large predatory mammals come up on board to. There's a couple I just want to point out because their truly ironic and memorable, one of them is as you see in this image, and again these are all artists reconstructions based on fossil evidence. One of them in the Olyga scene was the world's largest treasured carnivore that worth the million. And in this image you'll see that looks like a gigantic wolf. Well it haunted like a wolf and it acted like a wolf but it's not a wolf, it's a sheep. So this is actually ironically a sheep in wolf's clothing. And, you know, that's backwards from the story of the wolf in sheep's clothing. So this was the sentinel mammalian based land predator for the Cenozoic time period. Others that came on board were things like the rhinoceros. And the rhinoceros had some morphologies and characteristics in are all that different from modern day rhinoceros. You can see here that there's a horn that came out at, the horn actually kind of a flanged. It was flattened and it wasn't quite as pointed but the horns on the rhinoceros are something that's evolved through time as well. These were big, 2.5 meters at the shoulder. In the Cenozoic as well, we had the rise of the elephants. the early elephants weren't all that much like some of the elephants that we have today. Actually they had, instead of having their tusks come out from the upper part of the jaw, the tusks came out from the lower part of the jaw, and they would curl down and around the organisms. So we had the advent of mammalian diversification, this radiation into this immense eco space both in the world's oceans and on land that allowed the mammals then to diversify and become extremely diverse in this Cenozoic time period. One thing to keep in mind since the KT impact we haven't had any large, we have had small scale meteor impacts, but nothing large scale that would cause mass extinctions. So really what it is going to be is a story of earth changing in some fundamental ways such as in the Eocene, we had the development of The great ice sheets in the Antarctic. So from the time of the dinosaurs until the Eocene time period, we had an Earth with no major ice sheets. And then once the ice sheets rose up in the Eocene, then of course the mammalian populations that were on Earth would respond and evolve to this ever cooling and ever changing ice dynamic type of Earth that we have. So the early Cenozoic is a story of dynamically changing environments, cooling overall as the planet develops over time and then this massive radiation at a very rapid pace of the diversification of the mammals. [MUSIC]
