Lesson 10: Paleogeography and Plate Tectonics Flashcards
Today, the Earth has several continents: North America and South America, Europe and Asia, Africa, Australia, and Antarctica. In addition to these continents are large islands like Greenland, New Zealand, Madagascar, and the southeast Asian islands. However, if you were to travel back in time to the ___ period and observe the Earth from a distance, you would notice, instead of multiple continents, only a single, enormous continent was present on Earth at that time. This was a supercontinent called Pangaea.
Permian. (Actually end of Permian and beginning of Triassic)
In 1912, a German researcher named Alfred Wegener drew the scientific community’s attention to several curious facts. What were they?
Wegener had noticed that the eastern coastline of South America and the western coastline of Africa looked like two connectable puzzle pieces, that the fossils of many ancient animals (which, as
far as anyone could tell, were not animals that would have been capable of swimming across the Atlantic Ocean) could be found in both South America and Africa, and that several geologic formations in South America had seemingly identical twins in Africa. Wegener suggested that Africa, South America, and possibly other continents had once been connected and had since drifted apart. However, Wegener could not offer a convincing mechanism for how land masses as big and as seemingly immobile as continents could move.
Describe the Earth’s crust.
Below its surface, the earth is not a uniform mass of rock. The outermost layer of the earth consists of the continents and ocean basins and is called the crust. The thickness of the crust varies but is usually between 5 and 25 kilometers deep. By comparison to the other layers of the earth, the crust is thin.
Describe the Earth’s mantle.
Below the crust is a layer called the mantle. The mantle is a layer over 2,500 kilometers deep. The uppermost portion of the mantle is solid. Along with the crust, this upper solid portion of the mantle is called the lithosphere.
Describe the lithosphere.
Along with the crust, the upper solid portion of the mantle is called the lithosphere. The lithosphere is not one unbroken layer, but is actually composed of many discrete pieces, or plates, that fit together.
Describe the asthenosphere.
Below the lithosphere is a portion of the mantle called the asthenosphere. While the lithosphere is rigid, the asthenosphere is viscous, slowly flowing, and its shape may be deformed under the uneven weight of the lithosphere. Although it flows, the mantle is not a liquid, but a viscous solid that flows. The intense heat and pressure at great depths causes the solid mantle to behave like a fluid – similar to plasticine or playdoh that is a solid at rest, but that squishes when you squeeze it.
Describe the core.
Below the mantle is the core. The core is primarily composed of iron and nickel and is subdivided into the outer core and the inner core. The outer core is molten liquid, while the inner core is a solid ball. The temperature of the inner core is estimated to be roughly 5,700° C (the same as the surface temperature of the sun).
The movement of the lithosphere is called plate tectonics, and it provides the explanation for the drifting continents that Alfred Wegner theorized. Describe how it works.
The extreme heat of the inner layers of the earth creates convection currents in the viscous asthenosphere. Lower portions of the asthenosphere slowly heat, expand, rise upwards, and then slowly cool and sink. Plates, or pieces of the lithosphere, are affected by these currents. The currents pull along the undersurfaces of the lithosphere’s various pieces, causing them to slowly move. Additionally, the cool crust is more solid and dense than the layers below it. This causes lithosphere plates to slowly sink and to melt into the lower layers. This sinking does not happen all at once, but occurs gradually along one of the edges of a plate. As one edge sinks, a small gap is created along the opposite edge, and, through this gap, molten rock is free to escape. This rock then cools, solidifies, and adds its own mass to the edge of the plate. This cycle continues.
Plate tectonics has now been verified in a variety of ways. What are they?
The discovery of mid-ocean ridges revealed plate edges where new crust was being formed. Studies of mid-ocean ridges show that the crustal rocks on either side of the ridges have indeed been slowly drifting apart. Advanced global positioning satellites tracking systems can detect the ongoing movements of the continents and even record their speeds.
What is Panthalassa?
The single super-ocean during Pangea time.
What did dinosaurs typically look like during the late Triassic and early Jurassic?
Dinosaurs all across the world are fairly similar. Prosauropods and small theropods similar to Coelophysis are found worldwide.
The first true sauropods appeared very late in the Triassic, alongside their prosauropod relatives. During the Early Jurassic, while all the continents were still connected, sauropods rose to new heights, surpassing prosauropods in both abundance and body-size. Among the thriving Jurassic long-necks were the diplodocids. Describe them.
Even compared with other sauropods, most diplodocids have extremely long necks. They are also characterized by front legs that are much shorter than their hind legs, and by their unusual faces. The skull of a diplodocid is elongated and resembles the general shape of a horse’s or a deer’s. Diplodocid teeth are simple, peg-like, and are positioned only at the front of the mouth, not on the sides. They are nipping teeth – good for cropping off leaves and other tender growth.
Diplodocids shared their Jurassic world with another group of sauropods called the macronarians. Describe them.
Macronarians do not have the whip-tails of diplodocids. Their bodies are generally more robust, and their front legs are usually not noticeably shorter than their back legs. In fact, in macronarians like Brachiosaurus and Giraffatitan the front legs were much longer than the back legs. Most macronarians still have the long necks characteristic of sauropods, and they too filled the ecological niche of high browsers.
Give an example of niche partitioning in sauropods.
Consider the macronarian Camarasaurus and the diplodocid Diplodocus (the namesake of the group). In comparison, the snout of Camarasaurus is much shorter, and its teeth are not limited to the front. In fact, the teeth of Camarasaurus line the entire jaw, and the individual teeth are not simple pegs. They are broad, robust, and look like the heads of spoons. While Diplodocus has the mouth of a selective nipper, Camarasaurus has the mouth of a powerful muncher. Diplodocids were adapted to reach high and prune off the most delectable Jurassic foliage, while macronarians were less picky eaters. They could crunch much harder, even woody, vegetation, and they could eat what the diplodocids left behind.
Grazing and browsing in the shadows of sauropods were a variety of smaller Jurassic herbivores. Among them were the thyreophorans, a group that includes the ornithischians with body armor. By far the most well-know of the Jurassic thyreophorans was …?
Stegosaurus. Stegosaurs were a widespread group of thyreophorans in the Jurassic, and their fossils have been found in Africa, Asia, Europe, and North America.
Another group of common Jurassic ornithischians were the …?
Ornithopods. Small ornithopods had long legs and appear to have made up for their diminutive size with speed, earning themselves the nickname “Jurassic gazelle”. A few Late Jurassic ornithopods obtained greater size, like Camptosaurus – an early iguanodont.
The Jurassic niche of big predator was filled by an array of carnivorous dinosaurs. There were giant megalosaurids and ceratosaurids, both ancient lineages of theropods. But the Late Jurassic was a time of predatory change. A new group of big carnivorous dinosaurs had evolved, and they were mounting an ecological takeover. What were they?
The allosauroids were different from the big predators that had come before them. Allosauroids have vertebrae that interlock more rigidly, so their spines were held stiffer. Their legs are also proportionately longer, suggesting that they were faster than either megalosaurids or ceratosaurids. The allosauroid Allosaurus is known from more fossil skeletons than any other big theropod dinosaur, and it was clearly among the most successful of the Late Jurassic’s predators.
Not all the Jurassic carnivores were big. The chicken-sized theropod Compsognathus is among the smallest of all known dinosaurs. Describe it.
Like Allosaurus, Compsognathus has a more rigid spine and long legs, but it belongs to another theropod group. It is a coelurosaur. Coelurosaurs are characterized by a long series of sacral vertebrae, narrow hands, and tails with back halves that are skinny, stiff, and lightweight. Allosauroids might have been the biggest predators around at the time, but in the Jurassic, it was the coelurosaurs that spawned the dinosaurs’ greatest success: birds. And, in the Cretaceous, some coelurosaurs would evolve their way to the very top of the food chain.
During the Jurassic, Pangaea began to split into two massive continents. Describe them.
Laurasia was the northern of the two and was composed of what we today call North America, Europe, and Asia (excluding India).
Gondwana was the southern of the two and was composed of what we today call South America, Australia, Africa, Antarctica, Madagascar, and India.
As the continents drifted apart, so too did the populations of dinosaurs. Some groups went extinct in Laurasia or Gondwana, and some groups diversified.
By the Early Cretaceous, there were significant regional differences among the world’s dinosaurs. What were they?
Iguanodontians, ankylosaurs, and brachiosaurid sauropods were present in North America and Europe.
In Africa, the dominant theropods were the spinosaurs and carcharodontosaurids.
In Asia, coelurosaurian theropods became common, and the first ceratopsians evolved.
By the Late Cretaceous, Gondwana had begun to break apart into its constituent continents, but Antarctica and Australia remained connected until close to the end of the Cretaceous. Sauropod dinosaurs went extinct in Laurasia, but thrived in Gondwana. However, they were not the same sauropods that populated the Jurassic. The diplodocids had gone extinct during the beginning of the Cretaceous, and although the macronarians survived, the brachiosaurid macronarians did not. Instead, a new type of macronarian dominated: the titanosaurs. Describe them.
Titanosaurs are the most robust of all sauropods. Their chests are broad and their hips are wide. Their hind limbs are spaced far apart – giving them a very stable base. Many titanosaurs had osteoderms and some even had large spiky armor. Titanosaurs ranged in size, but among their ranks were animals like Argentinosaurus – a sauropod that has been estimated to weigh over a hundred tons, making it the largest creature to ever walk the earth.
With armor and sheer size to protect them, titanosaurs were not easy prey, but one group
of Late Cretaceous theropods may have been specialized giant slayers. What were they?
The carcharodontosaurs are named for the shape of their teeth, which resemble those of the Carcharodon – the great white shark. Carcharodontosaurs are a type of allosauroid, so they are descendants of the big theropods that first rose to prominence in the Late Jurassic. However, carcharodontosaurs differ from older allosauroids in a number of ways. Most noticeably, carcharodontosaurs have bigger heads, with longer jaws. As Late Cretaceous titanosaurs got bigger, so did carcharodontosaurs. The largest of all was the South American Giganotosaurus. At over thirteen meters in length, Giganotosaurus even out sized Tyrannosaurus rex.
There was room for more than one kind of big carnivore in the Late Cretaceous of South America. Name one other than carcharodontosaurs.
Abelisaurs, like the famous horned species Carnotaurus, were the last survivors of the ceratosauroid lineage, and some grew to over eight meters in length. In the Cretaceous, the group was strictly limited to Gondwana, but they evidently thrived there, as abelisaur fossils have been found throughout the southern hemisphere.
Living alongside carcharodontosaurs must have been tough, and the need for ecological niche partitioning drove abelisaurs to adapt a strikingly different morphology. Describe.
While carcharodontosaurs have long jaws with big teeth, abelisaurs have short muzzles and proportionately tiny teeth. While carcharodontosaurs tended to have powerful forearms with large hooked claws, abelisaurs had ridiculously short and stubby arms, with small claws. And, while carcharodontosaurs likely preyed on huge titanosaurs, abelisaurs are thought by many paleontologist to have hunted the smaller species of titanosaurs and other less daunting herbivores.
