Lesson 12: Dinosaur Extinction Flashcards
What are extant species? Extinct species?
Species that are still present today are called extant species. Species whose members have all died off are called extinct species.
Palaeontologists generally recognize five major mass extinctions. What are they?
- The End Ordovician mass extinction affected only marine organisms, but at that time terrestrial organisms had only just begun to evolve.
- The Late Devonian mass extinction was also largely limited to marine organisms, including some early vertebrate clades.
- The End Permian mass extinction saw the largest loss of diversity in all of Earth’s history. Marine invertebrates were decimated, and this was the largest mass extinction of insects. On land, the synapsids were hard hit, as were the anapsids (which we have not discussed much in this course, but which included large and small herbivores and some aquatic species).
- The End Triassic mass extinction saw the extinction of most lineages of pseudosuchian archosaurs, as well as many of the synapsids that had survived the End Permian extinction, and also affected marine life.
- The last of the “Big 5” extinctions was the End Cretaceous. The End-Cretaceous Extinction event occurred roughly 66 million years ago and killed all non-avian dinosaurs.
Who perished during the End-Cretaceous extinction?
Dinos were not the only casualties of this extinction. In the oceans, large marine diapsids, called mosasaurs and plesiosaurs, died out, as did many varieties of corals, several forms of plankton, and ammonites (relatives of modern squids and octopi). Pterosaurs went extinct as well. Although birds ultimately survived, many types of Cretaceous birds (including hesperornithiform and enantiornithiform birds) perished. Land plants also lost many species in the extinction, and insect diversity fell.
Who survived the End-Cetaceous extinction?
Mammals, turtles, crocodiles, amphibians, and fish all made it through the End-Cretaceous Extinction, although many of the larger species in all these groups did not. Generally, it seems that large animals and photosynthetic organisms were the most likely to die off. Small animals, and particularly those that were semiaquatic, had the best chance of surviving.
What are Champsosaurs?
These crocodile-like aquatic diapsids (completely unrelated to crocodilians, and another good example of convergent evolution at work) survived the End Cretaceous mass extinction, only to go extinct during the early Miocene (about 20 million years ago).
What are some of the most recent examples of extinction where species have been eliminated through the actions of humans?
- The thylacine (also called the Tasmanian tiger or Tasmanian wolf) was a large carnivorous marsupial that went extinct sometime went the last individual died in a zoo in 1936.
- The Carolina parakeet, the only species of parrot native to the USA, went extinct in 1918.
- Perhaps one of the most famous examples, the passenger pigeon, went extinct in 1914 even though there were billions of passenger pigeons only a few decades prior.
Although deliberate hunting does not play as much of a role in the depletion of modern animal populations, ___ ___ and ___ are significant contributors to the extinction of different species.
Habitat loss and pollution.
Describe some features of the layer of grey clay discovered at the Cretaceous/Paleogene boundary.
- It had high concentrations of iridium. Iridium is a rare element on earth, but it is a common component of meteorites.
- The layer was also rich in tektites and shocked quartz. Tektites are tiny pieces of rock that have been melted and then cooled. Shocked quartz is a form of the mineral quartz with a unique internal structure that can only be created by exposure to a powerful shockwave, like those created by a nuclear explosion or a meteorite impact. (These are telltale signs of a meteor impact)
Geologists working near the town of Chicxulub in Mexico’s Yucatán Peninsula noticed a peculiar pattern of cenotes, or limestone sinkholes. The cenotes were arranged in a crescent shape many miles long. How did they form and what did they mean?
Investigation revealed that the cenotes were caused by a displaced portion of a limestone layer that had been pushed upwards, and that the structure did not actually end at the edges of the peninsula. Instead, it continued along the ocean floor and was actually a huge continuous ring over 180 km in diameter. Radiometric dating revealed that this massive ring of displaced rock was 66 million years old. The crater made by the meteorite responsible for showering the earth with debris at the end of the Cretaceous had been found.
Based on the crater’s size, how large was the meteorite?
10 kilometers in diameter, larger than Mount Everest.
What are some proposed ideas for the end-cretaceous mass extinction that are improbable or hard to test?
- mammals eating dino eggs. They coexisted for 160 mil. yrs
- ice age (temp did drop after the cretaceous, but gradually. Mil. of yrs before true ice age)
- methane gas generated by dinos caused climate change
- nearby supernova
- viral outbreak (does not explain other extinct species at same time)
What are some of the more plausible explanations of the end-cretaceous mass extinction?
- A mass volcanic outgassing of carbon dioxide and ash plumes has also been suggested as a possible cause of the extinction. This scenario could potentially have affected the global climate enough to have caused the extinction of many kinds of organisms, and there is a record of high volcanic activity in the Deccan Traps of India at the end of the Cretaceous.
- A very large meteorite struck the Earth in the Yucatan peninsula.
Describe the current prevailing theory for the cause of the End-Cretaceous extinction whereby a very large meteorite struck the Earth in the Yucatan peninsula.
The initial impact caused huge tsunamis and sent a great cloud of super-heated rock and dust high into the atmosphere. The rocks and larger pieces of debris quickly fell to earth and started wildfires. Smaller pieces of debris next began to fall and, as they fell, were heated by air friction. This rain of hot dust raised global temperatures for hours after the impact and cooked alive animals that were too large to seek shelter. Small animals that could shelter underground, underwater, or perhaps in caves or large tree trunks, may have been able to survive this initial heat blast. Finally, much debris would have remained in the atmosphere for perhaps months or even years. The residual haze would have reduced sunlight, killing many plants and other photosynthetic organisms, with rippling effects up the food chain. The reduced sunlight may also have brought on a sudden drop in global temperatures.
Some scientists estimate that photosynthesis may have stopped (after the meteorite impact) for …?
At least a decade.
Who was more likely and least likely to survive the meteorite and subsequent events?
Being large active animals with high energy needs and positioned at the top of prehistoric food chains, dinosaurs were highly susceptible to this series of catastrophes. Smaller, omnivorous terrestrial animals, like mammals, lizards, turtles, or birds, may have been able to survive as scavengers feeding on the carcasses of dead dinosaurs, fungi, roots, and decaying plant matter, while smaller animals with lower metabolisms were best able to wait the disaster out.
