Lesson 10: Paleogeography and Plate Tectonics

Question 1

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.

Answer 1

Permian. (Actually end of Permian and beginning of Triassic)

Question 2

In 1912, a German researcher named Alfred Wegener drew the scientific community’s attention to several curious facts. What were they?

Answer 2

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.

Question 3

Describe the Earth’s crust.

Answer 3

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.

Question 4

Describe the Earth’s mantle.

Answer 4

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.

Question 5

Describe the lithosphere.

Answer 5

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.

Question 6

Describe the asthenosphere.

Answer 6

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.

Question 7

Describe the core.

Answer 7

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).

Question 8

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.

Answer 8

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.

Question 9

Plate tectonics has now been verified in a variety of ways. What are they?

Answer 9

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.

Question 10

What is Panthalassa?

Answer 10

The single super-ocean during Pangea time.

Question 11

What did dinosaurs typically look like during the late Triassic and early Jurassic?

Answer 11

Dinosaurs all across the world are fairly similar. Prosauropods and small theropods similar to Coelophysis are found worldwide.

Question 12

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.

Answer 12

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.

Question 13

Diplodocids shared their Jurassic world with another group of sauropods called the macronarians. Describe them.

Answer 13

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.

Question 14

Give an example of niche partitioning in sauropods.

Answer 14

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.

Question 15

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 …?

Answer 15

Stegosaurus. Stegosaurs were a widespread group of thyreophorans in the Jurassic, and their fossils have been found in Africa, Asia, Europe, and North America.

Question 16

Another group of common Jurassic ornithischians were the …?

Answer 16

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.

Question 17

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?

Answer 17

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.

Question 18

Not all the Jurassic carnivores were big. The chicken-sized theropod Compsognathus is among the smallest of all known dinosaurs. Describe it.

Answer 18

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.

Question 19

During the Jurassic, Pangaea began to split into two massive continents. Describe them.

Answer 19

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.

Question 20

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?

Answer 20

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.

Question 21

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.

Answer 21

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.

Question 22

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?

Answer 22

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.

Question 23

There was room for more than one kind of big carnivore in the Late Cretaceous of South America. Name one other than carcharodontosaurs.

Answer 23

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.

Question 24

Living alongside carcharodontosaurs must have been tough, and the need for ecological niche partitioning drove abelisaurs to adapt a strikingly different morphology. Describe.

Answer 24

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.

Question 25

___ and ___ were rare in South America, but a few species found in the latest Cretaceous suggest that there was a land bridge late in the evolution of the dinosaurs between North and South America.

Answer 25

Hadrosaurs and ankylosaurs.

Question 26

What is one of the biggest differences between the Late Cretaceous fauna of Laurasia and Gondwana?

Answer 26

The relative under abundance of sauropods in the north. While titanosaurs were abundant and diverse in Gondwana, they were far less common in Late Cretaceous Laurasia. In what is now Asia, titanosaurs were present, but comparatively rare components of the ecosystem. In North America, only a handful of titanosaur species are known.

Question 27

Although stegosaurs never made it to the Late Cretaceous, another group of thyreophrans did …?

Answer 27

The ankylosaurs.

Question 28

In Laurasia, ankylosaurs split into two major groups. What are they?

Answer 28

The ankylosaurids are the ankylosaurs with the famous tail clubs. Ankylosaurids also typically have large backwards-pointing horns at the rear of their skulls and a short rounded snout at the front. Nodosaurids are the second major group of ankylosaurs. They lacked tail clubs, but some have offensive weapons at the other end, in the form of large osteoderm spikes that project outwards from over their shoulders. Nodosaurids do not generally have the big skull horns of anklosaurids, and their snouts are significantly narrower and more elongated.

Question 29

After their start in the Jurassic, iguanodont ornithopods thrived and became common across the globe, during the Early Cretaceous. In Laurasia, a new kind of iguanodont evolved …?

Answer 29

The hadrosaurs. Hadrosaurs flourished in the Late Cretaceous and quickly became the northern hemisphere’s most successful herbivorous dinosaurs. We have more fossils of hadrosaurs and know more about hadrosaur biology than any other major dinosaur group.

Question 30

Among advanced hadrosaurs, there are two major groups. Describe the lambeosaurine hadrosaurs.

Answer 30

The lambeosaurine hadrosaurs had big crest on their heads, which can be thought of as a kind of musical instrument. Inside a lambeosaurine crest is a complex and hollow nasal passageway. Blowing air through this passage and then out the nostrils would have amplified the dinosaur’s calls. The hollow crests of lambeosaurines come in a variety of sizes and shapes.

Question 31

Among advanced hadrosaurs, there are two major groups. Describe the hadrosaurine hadrosaurs.

Answer 31

The second major group of advanced hadrosaurs is the hadrosaurines (sometimes called the saurolophines). From the skulls of hadrosaurines, it is clear that they do not have the complex sound amplifying crests of the lambeosaurines. However, some hadrosaurines do still have crests. For instance, the hadrosaurine Saurolophus had a prominent, but solid, bony crest. Recently, a fossil mummy specimen of the hadrosaurine Edmontosaurus was discovered in Alberta, Canada, with a big fleshy crest, like the comb of a rooster, preserved on the top its head. This specimen revealed that at least some hadrosaurines had large crests, even though their skulls provide no record of them.

Question 32

Running a close second to hadrosaurs, in terms of Laurasian diversity and success, was another group of herbivorous dinosaurs …?

Answer 32

The marginocephalians. That name literally means “fringe heads” and refers to an overhanging lip of bone at the back margin of the skull. Pachycephalosaurs are one of the two major groups within the marginocephalians. The other is the ceratopsians.

Question 33

The first ceratopsians are a far cry from the later and famous forms, like Triceratops. Primitive ceratopsians, like Psittacosaurus, are small and bipedal dinosaurs, but they still show a few family resemblances. Describe them.

Answer 33

Like all ceratopsians, they have large beaks and small, jugal cheek-horns projecting from the sides of their face. Psittacosaurus and other primitive ceratopsians are well known in Asia, but the larger, more derived ceratopsians, like Triceratops, are known almost exclusively from North America.

Question 34

For much of the Cretaceous, the allosauroids were the top predators throughout Laurasia, just as they were in Gondwana. But they were rivaled by another theropod group. Coelurosaurs blossomed into the most diverse of all theropod groups, and they gave rise to the most infamous of all predatory dinosaurs …?

Answer 34

The tyrannosaurs.

Question 35

By the end of the Cretaceous, tyrannosaurs came to dominate the niche of alpha predators throughout Laurasia. To some extent, tyrannosaurs achieved their success by taking to a further extreme the same adaptations that had once set the allosauroids apart from their competitors; that is, tyrannosaurs evolved even longer legs and a much stiffer vertebral column. However, tyrannosaurs also evolved …?

Answer 35

Massive skulls with tremendous jaw muscles. The earliest tyrannosauroids, like the Asian species Dilong and Guanlong, or the European species Eotyrannus, have normal head and body proportions, and they look similar to most other small coelurosaurs. But as tyrannosaurs evolved, they grew in absolute size and in the relative size of their heads. These big heads added weight to the front half of their bodies. To compensate, tyrannosaurs reduced weight by shrinking the size of their arms and hands – culminating in the last and largest of all tyrannosaurs Tyrannosaurus rex.

Question 36

Not all Cretaceous coelurosaurs were huge and predatory. Describe ornithomimids.

Answer 36

Ornithomimids are a kind of coelurosaur that evolved a body plan similar to that of a modern ostrich or emu, but with long clawed forelimbs and a large tail.

Question 37

Not all Cretaceous coelurosaurs were huge and predatory. Another group of coelurosaurs developed a highly specialized wrist bone called a semilunate carpal. What are they?

Answer 37

These crescent-shaped bones allowed the hand to be folded backwards at a sharp angle, and the dinosaurs that possess them are called the maniraptorans.

Question 38

What are some examples of maniraptorans?

Answer 38

Birds are one group of maniraptorans, and the semilunate carpals of birds allow them to delicately fold their wings when not flying. As close relatives of birds, the sickle-clawed dromaeosaurs are also maniraptorans, and so are the oviraptorosaurs.

Question 39

Describe oviraptorosaurs.

Answer 39

Like ornithomimids, oviraptorosaurs are a group of theropods that adapted to a mostly vegetarian life and lost their teeth in favor of large beaks. Many oviraptorosaurs had cranial crests and fans of feathers on the ends of their tails.

Question 40

Perhaps the strangest of all Laurasian coelurosaurs are the therizinosaurs. Describe them.

Answer 40

The first theriznosaur fossil to be found was a huge claw, over 60 cm long. It was mistaken for the claw of a giant turtle. Therizinosaurs have small skulls on the end of long necks and hind feet with four forward pointing toes, so some paleontologists thought they might be prosauropods. Therizinosaurs also have a backwards-directed pubis and jaws with small herbivorous teeth in the back and a beak in the front, so some researchers classified them as ornithischians. Several fossil skeleton discoveries and a lot of research later, paleontologists are now in agreement that therizinosaurs are maniraptoran theropods (close relatives of oviraptorosaurs).

Question 41

What is faunal interchange?

Answer 41

Sometimes plate tectonics brings continents that were once separate back together. When this happens, dinosaurs from one region can move into another, leading to similar species in both regions.

Question 42

Give an example of faunal interchange.

Answer 42

The Late Cretaceous dinosaurs of Alberta are very similar to those found in Mongolia, which suggests that there was immigration between these two areas during the Late Cretaceous; Asia and North America were probably intermittently connected via Alaska at this time. Theropods are represented by tyrannosaurs, dromaeosaurs, therizinosaurs, ornithomimids, and oviraptorosaurs; ornithischians in both areas include hadrosaurs, ceratopsians, ankylosaurs, and pachycephalosaurs.

Question 43

Why were temperatures higher during the age of dinos?

Answer 43

This warmer global climate was largely caused by high volcanic activity, which released large quantities of carbon dioxide into the atmosphere. Carbon dioxide is a greenhouse gas that holds in solar heat. The concentration of all Earth’s land masses in only one or two supercontinents may have also been a factor that contributed to the high average temperatures, because it affected the circulation of both air and water currents through the polar regions.

Question 44

Ocean currents are extremely important to distributing and moving heat from one part of the earth to another. Give an example today.

Answer 44

Today, the Gulf Stream is an ocean current that flows from the Gulf of Mexico to the western coast of Europe. Gulf Stream water is warmed in the Gulf of Mexico and this heat is carried north as it flows. The Gulf Stream makes many European countries much warmer than places of similar latitudes on the other side of the Atlantic.

Question 45

Give another example of the importance of ocean currents in distributing heat.

Answer 45

Today a strong and cold ocean current encircles much of Antarctica, and this current helps to keep Antarctica cold. However, 70 million years ago, when Antarctica was still attached to Australia, this current had to go up and around Australia. As the current moved through more equatorial areas, it become warmer, and then, as it flowed back down, carried this heat to Antarctica.

Question 46

During the Mesozoic, what were in the arctic and Antarctic circle?

Answer 46

Antarctica and Australia were located within the Antarctic Circle, and parts of North America were located above the Arctic Circle (North America was actually located further north than it is today).

Question 47

Although it was once assumed that dinosaurs were limited to warm tropical climates, it is now known that many varieties of dinosaurs thrived in polar regions. What are some?

Answer 47

The Early Jurassic theropod Cryolophosaurus, and the prosauropod Glacialisaurus, were discovered in Antarctica, along the Transantarctic Mountains. The small ornithopod Laeallynasaura inhabited what were then polar forests in the Early Cretaceous of Australia. The Late Cretaceous of Alaska was home to a diverse assemblage of dinosaurs similar to what is found in Alberta, including the hadrosaur Edmontosaurus, the tyrannosaurid Albertosaurus, and the ceratopsian Pachyrhinosaurus.

Question 48

What contributed to higher sea levels in the Mesozoic?

Answer 48

No polar ice caps and glaciers, and thermal expansion,.

Question 49

During the Mesozoic, sea levels were up to ___ m higher than they are today.

Answer 49

250 m.

Question 50

Higher sea levels resulted in the flooding of vast regions of the earth, limiting the amount of exposed land and splitting areas that are now connected into isolated islands. Give an example.

Answer 50

For example, during the Late Cretaceous, much of the interior of North America was covered by a massive inland sea. This vast waterway, called the Western Interior Seaway, spread from the Arctic Ocean to the Gulf of Mexico.

Question 51

At various points during the Mesozoic, North America was subdivided into two separate island subcontinents. Describe them.

Answer 51

Laramidia in the west, from which the majority of North American dinosaur species are known, and Appalachia in the east, from which far fewer dinosaurs are currently known.

Question 52

Because of this ancient sea, Mesozoic marine fossils can be found in parts of Alberta and throughout the American Midwest, because these regions were underwater during much of the Mesozoic. In southern Alberta, marine sediments called the ___ ___ have produced the remains of marine reptiles like mosasaurs and plesiosaurs, and invertebrates like ammonites (relatives of today’s nautilus).

Answer 52

Bearpaw Formation.