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13. Mesozoic I.docx

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Jessica Hawthorn

MESOZOIC – DINOSAUR I Today, we’re going to do something different than we’ve done for every other lecture. We’re going to talk about dinosaurs. The remainder of this class is going to be divided between looking at the Mesozoic and the Cenozoic, culminating in our world today. We’re done with the Palaeozoic. The Mesozoic is the middle interval. It is broken down into three time periods: the Triassic (248-206), the Jurassic (206-144), the Cretaceous (144-65). Thi sis called teh age of dinosaurs. It is an interval of pronounced climate changes, and it is the interval of the most dynamic plate tectonic activity in the phanerozoic. It is also the interval where we see the origins of the most of the modern groups of animals wtaht we would recognize today. The first interval, the Triassic 248-206 mya. Here’s what we have. The Triassic is characterized by a couple of things: the breakup of Pangea becomes important. We have the first occurrence of animals like turtles, frogs, modern groups of fishes, and dinosaurs. We have hte beginning of whaat is called the mraine arms race.we have he origin of ammals. We have the radiation of initial modern plants. At the end of the Permian, what was previously during the laurentia and gondwana had formed together. Africa collided wit hte east cost of NA...conglomeration of landmasses into single giant landmass called pangea. During the Triassic, we see the intial fragmentation of pangea. It begins to break apart. We have the intial opening of what is today teh north atlantic ocean, the gulf of mexico. How many people know where the atlantic ocean is? Everyone knows. The ocean between ocean between Africa and South America, and between Europe and North America. If you were to take all of the continents today as puzzle piec, you could connect them altogether. North America: single clarge continental land mass. The equator is considerably south relative to its position today. Where was the equator during paleozoic: drunnning through tornoto. Now, the NA landmass has oriented itself something akin to what we have today, even though it is considereaably south. It is a single landmass, there is the appalachain mountain range along the east, formed from the intial collision and formation of pangea. This land mass...NA relative to Africa nad SA. We have the intial spepartion of this landmass into a northern landmass and a southern landmass. The first separation occurs in the north atlantic. Europe and NA. We have the separation of the margins of Africa and South America. What happens in plate tectonics when two pieces of continental crust get pulled apart: ocean crust. It forms thin, dense, basalt crust. It forms a low crust. The low spot will open up and flood as the continents move apart. At the top, you have Evaporates aer rock deposits that are formed when you have the evaporation of water. We have areas that have the solid residue of what happens when water is evaporated. Has anyone been to the southwest part of the US (Grand Canyon). You get them when you drain out and evaporate an ocean basin. So, as we begin to rift these continents apart, we form oceanic crust, adn we get periodic flooding of those areas from ocean waters as the continents move apart. We can see that by the distribution of the evaporate deposits. So, we have this separation of pangea. What does this look like. The cross section: you have basically the separation of two places as they move away from each other. They don’t just break apart like a paper cut cuts your skin. Instead, teh crust is fairly rigid. It breaks into a series of blocks. As these blocks break apart, some of them drop down a little bit. Just lke blood out of a paper cut, magma material moves up and comes up to the surface, expressed as volcanoes or basalt flows. As these plates continue to move apart, you will have evaporates forming as ocnea water comes in and ries out constantly. You’ll get ocean basins so well developed that you have continuous ocean water there, and you form ocean environments. This is what is beginning to happen in the Triassic. NA, Europe, and Africa separating from eac other. You’ve also heard of petrified forest, AZ, Records Triassic forests. We have petrified logs, thousands of them. You’re looking at a 230 million year old log lying on its side. These forests are composed of plants of partly modern origin. We have confiers, we have cycads, we have the gropu that goes onto form flowers and plants, and we have an abundance of lycopsids (but there diversity has decreased). We’re see radiations of sea ferns and of conifers. There are no flowers. There is no fruit. These reproductive structures have not evolved in the Triassic. Lots of cycads and cone-bearing plants and lots of ginkos. What are ginkos. If you go farther south than Ontario, you’ll run into these plants. They’re their own separate lineage. They have meaty seeds. The seeds decompose in such a way that they smell exactly like vomit. Alive ginkos and fossil ginkos. Real trees and fossil logs. There were no grasses at this time. The majority were ferns. In marine environments whichi were devasted by the Permian extinction event, we have recovery. Increasing diversity wit hmodern groups taking over. In teh paleozoic, there were brachiopods, in the Mesozoic, you get molluscs and clams (of modern origin ) which dominate. They diversity and radiate. We have trifea and corals. Corals today are primary reef builders. Corals and reefs are engines of biodiversity. They are areas where large numbesr of species evolve. At the end of the Permian, all the primitive corals that formed the reefs of the Permian go extinct. You can se the big cliffs. Those are giant coral reefs in West Texas. They represent the end of primitive corals. By the middle o the TRiasc, we see ocrals coming back, and they’re the modern corals. Echinoderms (deuderostomes related to us) these are sea urchins. They diversify. What is that at the bottom. That is the skeletal remains of an echinoderm. You get a diversification of cephalopods (squid and octopus). That up there is the only living shelled cephalopod in modern ecosystems. We have a big radiation of shelled molluscs. You’re seeing coiled shells of a gropu of mollsuss called ammonites. They’er the most diverse Mesozoic cephalopods. Biostratigraphy sues teh distribution through hthe rock reocord of fossios to correlate different packages of rocks. Ammonites are one of the primary animals for correlating marine rocks during hte Mesozoic. We have a lot of animals that evolve shells. Then, what we have this evolution of shell-crushing predators: crustaceans (modern) diversify during hte Mesozoic. There are arthropods and crustaceans going all the way back, but we get the modern groups in the Mesozoic. They use massive, specialized shell-crushing claws. Harder, thicker shells evolve in resistance to shell-crushing claws. It isn’t just the invertebrates. We get hte first shell-crushing fishes. This is called a picnada. This happens in marine reptiles. Ther is a group called placodonts. They’re related to lizards. This is a group of aquatic reptiles that evolve and radiate out turing the Mesozoic and Triassic with big teeth. Specialized for Shallow marine sands looking for shell fish. Other marine radiations and reptiles. One of hte things that happens repeatedly in vertebrate evolution is that tetrapods and amniotes (reptiles and mammals, and their common ancestors), whih aer primitively terrestrial. There are repeated events where terrestrial animals evolve to life in oceans. Whales are an example. Sealions and walruses. Polar Bears. Sea Cows. Any reptiles that live in ocean environments. Sea snakes and marine aguanas. These animals are not hyper special, but in the Mesozoic, we have radiation and domiatnion among vertebrates by reptiles. At the top is a Sauropterygians. Then, there is the ichthyosaurs (fish lizard) at the bottom. This is one of his favourite fossils. It is preserved in a way that. The tip of his mouth is there. There are paddles, big rib cage going to the tail. These were marine animals that d
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