Hi and welcome back to extinctions, past, present, and future as we inch ever so closer to the present. To do that, we'll need to jump forward almost 66 million years from the end of the Cretaceous period to the end of the Pleistocene epoch. As you recall in our previous discussion of geologic time, the largest time divisions are eons, which are divided into eras. Eras are then divided into periods, and periods are composed of epochs. For example, the Cenozoic era, which follows the Cretaceous period and Mesozoic era contains three periods, the Neogene, Paleogene, and Quaternary. The Paleogene is then comprised of the Paleocene, Eocene, and Oligocene epochs. Whereas the Neogene period has the Miocene and Pliocene epochs, and the Quaternary period has the Pleistocene and Holocene epochs. The Cenozoic era is often nicknamed the Age of Mammals, which might be a little biased considering that we're mammal saying that. But with dinosaurs out of the way, these vertebrates evolved quickly and in many directions. Today, we have more than 5,000 species of mammals ranging from Etruscan shrews to the blue whale. The latter being the largest animal in earth history. Mammals have also occupied nearly every environment from mountains to seas and skies and filled a huge variety of ecological niches. However, not all of the dinosaurs died at the end of the Cretaceous. After all, birds are dinosaur descendants and are actually represented today by about 10,000 species, twice the number of mammals. So you could say that we're still living in the age of dinosaurs. In other biological recovery news, flowering plants, grasses, insects, amphibians, reptiles, coral reef sharks, bony fishes, molluscs, crustaceans, and many other organisms thrived and diversified throughout the Cenozoic era, with only a few lesser extinction events along the way. The diversification of mammals also involve what turned out to be one of the most eventful evolutionary events in the history of the earth. It happened in Africa during the Miocene epoch, about seven million years ago, when chimpanzees and humans split from a common ancestor. Thanks to much recent research in genetics and paleontology, we now know the evolutionary tree that led to our species, Homo sapiens really is more of a family bush than a family tree. It had many relatives that evolved and became extinct during the Miocene, Pliocene, and Pleistocene epochs. These relatives of chimpanzees and other apes are broadly placed under one evolutionarily-related group, hominins, which includes australopithecines and human relatives under the genus Homo. Based on all of the best scientific evidence, early species of Homo evolved and moved throughout Africa between 1-2 million years ago. Then, they left Africa, starting more than a million years ago. From there, they spread throughout Europe and Asia. During that time, outside of Africa, these human ancestors evolved and lived in the same European and Asian ecosystems as some of the most impressive land animals of the Cenozoic era, which we call with much reverence and awe, the Pleistocene megafauna. Today, megafauna is defined as any animal exceeding 44 kilograms in weight or about 100 pounds. During the Pleistocene epoch, which lasted from 2.5 million to just 11,500 years ago, animals that fit this criterion were far more common than today, and they were distributed on all continents outside of Antarctica. These big land dwelling animals were mostly represented by mammals, but also included a few birds and reptiles, which we'll talk about in future lectures. The European and Asian megafauna included elephants, some similar to those in Africa, but also, woolly mammals. Other large mammals were rhinoceros, both woolly and not so woolly, giant deer, cave lions, a few other large cats, cave bears, hyenas, and hippopotamuses. There were also other species of bears and deer, as well as wolves, wild boars, bison, and aurochs, the ancestors of modern domestic cattle. Meanwhile, a little more than 300,000 years ago, our species originated somewhere in Africa, although it's tough to narrow down exactly when and where. The oldest human fossils and artifacts are in Morocco, but slightly younger fossils and artifacts have been found in southern Africa. Regardless, this evidence shows that human populations were widely distributed throughout Africa. Then, about 65-70,000 years ago, a few groups of Homo sapiens left Southern and Eastern Africa and spread throughout the Middle East, Europe, and Asia. Remember that other species of Homo were already out of Africa and evolved in Europe and Asia. So our species was more like Johnny come lately's or Jane come lately's or well, you get the point. Perhaps, the most famous of these other species and our closest relative was Homo neanderthalensis or Neanderthals. These people originated about 400,000 years ago, and lived in Northern Europe and parts of Asia. What happened to the Eurasian megafauna? If you came into this lecture hoping for a high body count, you're going to be disappointed. Pleistocene megafauna extinctions and rates of extinction in Europe and Asia were relatively low, taking place over the last 100,000 years or so of the Pleistocene. Who were the casualties? Almost all elephants and mammals, giant deer, cave lions, and cave bears eventually vanished, as did all hippos and hyenas outside of Africa. But plenty of megafauna survived. The Indian elephants, various species of deer, wolves, bison, boars, and aurochs. So these megafauna extinctions were significant, but they weren't a devastating loss of every big animal in Europe and Asia. Almost all of the African megafauna survived, which is a point we'll come back to in a future lecture. Did all of the Pleistocene megafauna extinctions in Europe and Asia happen as soon as Homo sapiens showed up? Not exactly because these extinctions happened over the last 100,000 years of the Pleistocene, and modern humans were not in these areas until about 60,000 years ago. They didn't perfectly coincide, yet by the end of the Pleistocene, at about 11,500 years ago, almost all of the megafauna were already extinct. Amazingly, one small population of woolly mammals survived until only about 4,500 years ago on Wrangel Island, north of Siberia, but then, they died out too. So if you're more of a glass half full optimist, it sounds like the Pleistocene megafauna extinctions in Europe and Asia were not so terrible. Nonetheless, I should point out that one species of late Pleistocene megafauna did vanish soon after the arrival of Homo sapiens, the Homo neanderthalensis. Within only a few thousand years after our species appeared in Europe and Asia, Neanderthal numbers decreased, and by about 40,000 years ago, they were gone. The exact cause of their extinction is still unknown, but one explanation is that modern humans competed with them for resources in the same ecosystems, and Neanderthals lost at ecological contest. Nevertheless, a vestige of Neanderthals lives on today, as some people of European and Asian descent have genes linked to Neanderthals. This means modern humans and Neanderthals mated and successfully passed on their mixed genes to future generations persisting through today. So you might say in a sense, they're not quite extinct, and if you call someone a Neanderthal, you could be partially right. What about the Pleistocene megafauna outside of Africa, Europe, and Asia? Arguably, the most awesome examples were in the Americas, with each continent hosting a complement of big mammals that dominated their landscapes. That is, until almost all were wiped out by the end of the Pleistocene epoch. Who were these animals, and what happened to them? That is the subject of our next lecture.
