In the last module we talked about dinosaur origins. Now, we want to know why many of them went extinct. Let's start to answer this question by using a technique we've used so often in this course, by looking at modern animals for answers. >> Which of these animals are now extinct? Check all the answers you think are correct, A, Dimetradon, B, Mammoth, C, Smilodon, D, Trilobite. There are many groups of animals that are no longer alive today. Things like trilobites, which were very pervasive in the Paleozoic era, did not survive the end Permian extinction. Dimetradon, which gave rise to animals like mammals. Went extinct way back in the Triassic period, other animals like the saber tooth cat and the mammoth are extinct species that still have close living relatives, like lions and elephants. All of these animals are now extinct. So, a, b, c and d are correct answers. >> Just as new species of animals have evolved throughout the history of life, so to have species ceased to exist. When all of the individuals of a species are gone, that species is extinct. Unfortunately many species have recently become extinct through the results of human activities. The thylacine marsupial wolf went extinct in 1936, due to hunting and disease. The carolina parakeet, the only parrot native to the United States, went extinct in 1918 because of deforestation and the demand for its feathers in the fashion industry. Perhaps one of the most famous recent extinctions was the passenger pigeon. The last member of this species died in 1914, the result of deforestation and hunting. When extensive hunting of the passenger pigeon first began, there were about five billion passenger pigeons. But even their great numbers did not prevent them from going extinct. Species that are still present today are called Extant. But even some extant animals are on the brink of extinction. For example, less that 60 Javan rhinos remain in the wild. And the Speksnocaz are extinct in the wild. The species survives only in captivity. Sometimes animals can be brought back from the brink of extinction through intensive human efforts like captive breeding programs. California Condors were saved in this way after the species had plummeted to only 22 individuals. While many species have become extinct through the actions of humans, extinction is also a natural process that has occurred countless times throughout Earth's history. >> Species arise and go extinct all the time. On average, how long does a species last? Before it goes extinct. Is it 100 thousand to one million years? One million to ten million years? Or ten million to twenty million years? The answer is B, one to ten million years. Of course, there are exceptions with some species coming and going much quicker or lasting much longer. This means that if there are about 10 million species on Earth, on average, one species should go extinct every year just due to natural causes. >> Although species are going extinct all the time, there are times in history when many species have all gone extinct at once. If you remember from the last module, we talked about how at the end of the Permian and at the end of the Triassic there were mass extinctions where over half of the species alive went extinct. Over a very short period of time. As well, there were two other mass extinctions before these. One at the end of the Ortivision and one at the end of the Devonian. The most recent mass extinction was at the end of the Cretaceous, About 66 million years ago. It was the end Cretaceous extinction that wiped out all of the non-avian dinosaurs. >> Non-avian dinosaurs weren't the only animals to go extinct during the end cretaceous extinction. Which of the following groups also went extinct at this time? Multiple answers may be correct, so check all the ones you think are right. A, ammonites, B champasaurus, C mosasaurs or D multituberculate mammals? Both the very abundant ammonites and sea living mosasaurs went extinct. There were a number of groups though like the multituberculate mammals,. And crocodile-like champsosaurs that made it through the end of the Cretaceous period, only to fade into extinction millions of years later. >> We're here in the University of Alberta Paleontology Museum. Where we have on display a wide selection of animals, that are alive before and just after End Cretaceous mass extinction. Although the land was still dominated both in total numbers and in size by the non-avian dinosaurs at the end cretaceous. Many of the groups of animals, we're familiar with today had already evolved,. For example, birds had already become diverse and well-established. Although they were mostly represented by groups no longer alive today. Like the tooth hesperorniforms and eneantiornithiforms. Birds would later undergo an explosive adaptation radiation after the end cretaceous extinction. Rapidly evolving into the major groups we see today. The Terrasaurs, unlike birds, did not survive the extinction event. The Terrasaurs were the largest flying animals ever to have evolved. Most mammals were small shrew or mouse size insectivores. And were only distinctly related to modern placental and marsupial mammals. One of the most common groups of mammals in the Cretaceous were the multituberculates, represented by this Kamptobaatar I have here. Virtually the only record we have of these mammals consists of their small, isolated teeth. They along with the more familiar placenta mammals, like this distant relative of modern day deer. And just to orient you, here is the nose, the orbit and the teeth. As well as marsupial mammals, represented by this opossum jaw I have here. These guys survived the end cretaceous extinction. However, by about 35 million years ago, multi-turburkulit's were extinct. Turtle's like this soft shelled Esperadis, were also common animals both before and after the end of the cretaceous. Crocodiles were also a group that was common both before and after the mass extinction. The crocodiles and turtles. May have survived the mass extinction because they both inhabit fresh water environments. A very recent paper has suggested that animals in fresh water aquatic habitats seem to have [INAUDIBLE] the mass extinction far better than groups in other habitats. Vegetation at this time included things like ferns. Moss, coniferous trees, and flowering plants. For much of the Mesozoic, forests were dominated by conifers. However, starting in the mid crutaceous flowering plants began to become the dominant vegetation in forests. Near the end of the Cretaceous the oceans were full of familiar creatures, like plankton, clams, snails, bony fish, and sharks. But there were also animals that are now extinct. The nautilus like ammonites, several kinds of reef building corals, the giant marine lizards called mosasaurs. And the marine reptiles called Plesiosaurus. One interesting group of animals that survived the end crutaceous extinction but is no longer alive today is the or the champsosaurus. The champsosaur were superficially crocodilian like but had a distinct evolutionary history. They survived the end Crutaceous extinction, but were extinct by the end of the Eocene period, about 33 million years ago.
