In the context of drifting continents, rising and falling seas, and different climates, different dinosaur populations found themselves isolated and facing different environmental challenges. These challenges pushed dinosaurs to evolve a wide array of adaptations over 160 million years of time. In this section, we're going to trace that history across an ever changing, global landscape. If you could travel backwards in time to the Mesozoic era, what dinosaurs would you most likely see? The answer depends on when you were looking, and where in the world you were. Right now, I'm in Alberta, Canada. If I remained in place and were able to travel back in the time to the very end of the Mesozoic era, I would see a different set of dinosaurs than someone doing the same in Africa, Australia, or South America. On the other hand, someone in Europe or Asia would see similar dinosaurs to some of those I was looking at, although the specific genera and species would be different. Now let's say I traveled back to a point before the dinosaurs were so globally diverse, to the late Jurassic Period, 156 million years ago. Dinosaurs in Alberta were rare at this time, but are common just south of the Canadian border in the United States. Behind me is one of the most common dinosaurs from the Jurassic fossil beds of Wyoming and Colorado, Camarasaurus. The Jurassic was the golden age of long necked dinosaurs. And browsing high in the Jurassic trees, Camarasaurus would've been joined by many other species sauropods. You'll recall that the late Jurassic was the heyday of theropods. Among the thriving Jurassic long necks were Diplodocids. Most diplodocids probably used their long necks to reach high into the trees where they used their simple front teeth to nip off the most tender leaves. Some paleontologists suspect that diplodocids were able to extend their treetop reach even further by rearing backwards and standing on their hind legs while bracing themselves with their tails. Diplodocid shared their Jurassic world with another group of sauropods called the macronarians. Jurassic macronarian sauropods include animals like this chimerasaurus. Macronarian bodies are generally more robust than diplodocid, and some had long front legs. And most had the long necks characteristic of Sauropods, so they too filled the ecological niche of high browsers. A niche is an animal's way of life. Think of it like the animal's job in the ecosystem. It's how a particular species makes its living. With so many kinds of sauropods living side by side in the late Jurassic period, it might seem like the niche of high browser would've been filled many times over. Sauropods should have faced excessive competition for food resources, but that wasn't the case. Take a close look at the skull of this Camarasaurus and compare it to diplodocids. You can see that the snout of Camarasaurus is much shorter and that its teeth are not limited to the front. In fact, they line the entire jaw. Now, look at the individual teeth. They're not simple pegs. They are broad, robust, and look like the heads of spoons. Diplodocid has the mouth of a selective nipper. But Camarasaurus has the mouth of a powerful muncher. Diplodocid were adapted to reach high and prune off tender leaves while Macronarians were less picky eaters. They could crunch much harder woody vegetation. Essentially, they could eat what the diplodocids left behind, thus. These two rather similar animals avoided direct competition for food resources. This is an example of a common ecological phenomenon called niche partitioning. If two species try to occupy the exact same niche, they will compete with one another. Although one species may out compete the other, both species will suffer from the competition. Thus, competing species will always have an evolutionary pressure to adaptively diverge from each other, and to become specialized to fill different unoccupied niches. A healthy ecosystem contains a diversity of species filling numerous ecological niches. In the Jurassic period, which of the following dinosaurs had a feeding niche most similar to that of modern elk and deer? Was it A) Giraffatitan. B) Pachycephalosaurus. C) stegosaurus. Or D) triceratops. Modern deer and elk are herbivores adapted to feed by both grazing on low plants and browsing on medium height plans. They have relatively narrow snouts, and can selectively consume a quality plant material over quantity. Giraffatitan had a very different herbivorous niche and was a high browser. Triceratops and pachycephalosaurus may have both niches similar to those of deer and elk. But you will remember from an earlier lesson, that both of these dinosaurs are from the Cretaceous period. Stegosaurus may not look like much of a deer or elk, but it is thought that stegosaurs were selective feeders capable of both low grazing and medium browsing. And this dinosaur lived during the Jurassic period. So, C is the correct answer. A variety of smaller Jurassic herbivores were grazing and browsing in the shadow of the Sauropods. Among them, were the Thyreophorans. That's a group that includes Ornithischians with body armor, like this Stegosaurus. Stegosaurs were a widespread group of Thyreophorans in the Jurassic period. And their fossils have been found in Africa, Asia, Europe and North American. Another group of common Jurassic Orniothicians were the ornithopods. Small Ornithopods had long legs, and appear to have made up for their diminutive size with speed. A few late Jurassic ornithopods obtained greater size like Camptosaurus, an early Iguanodon. The niche of big predator was filled by an array of carnivorous dinosaurs. There were giant megalosaurids and Ceratosaurids. Both are 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. This is Allosaurus, and it belongs to the theropod group known as the allosauroids. The allosauroids were different from the big predators that had come before them. For one, their vertebrae were more rigidly attached to each other. So their spines were stiffer. Their legs were also proportionately longer, suggesting that they were faster than either megalosaurs or soratasaurs. We've found more Allosaurus skeletons than any other big theropod dinosaur. So it was clearly among the most successful of the late Jurassic predators. Of course not all the Jurassic carnivores were big. This is a skeleton of the turkey sized theropod, Ornitholesias. Like Allosaurus, Ornitholsias had a more rigid spine and long legs. But it belongs to theropod groups, it's a Coelurosaur. Coelurosaur's are characterized by a long series of sacral vertebrae, narrow hands and tails with hack halves that are skinny, stiff, and light weight. The late Jurassic must have been a terrifying time for Coelurosaurs. They were predators, but at this size, they could have only hunted small mammals, lizard like reptiles, insects, and in at least a few piciverous species small fish. They could have easily been crushed underfoot by Sauropods, Therioforans, or big Ornithopods. And they were certainly an occasional snack for Allosauirds and the other theropods. They were also food for various non-dinosaur predators like Jurassic crocodiles. But in the Jurassic, it was the Coelurosaur that spawned the dinosaurs' greatest success, birds. And in the Cretaceous, some Coelurosaurs would even evolve their way to the very top of the food chain. Now let's flash forward in time to the late Cretaceous period. After nearly 50 million years of evolution and plate tectonics, a great deal has changed. The super continents Gondwana and Laurasia have split from one another. And some dinosaur groups have thrived and multiplied, while others have declined and become extinct. On Gondwana in the southern hemisphere, one feature of the Jurassic has remained constant: the sauropods still reign supreme as the dominant large herbivores. However, these are not the same Sauropods that we met in the Jurassic. There are no Camarasaurs or Brachiosaurs. Instead, a new type of macranarian evolved, the titanosaurs. Titanosaurs were the most robust of all saurapods. Their chests were broad and their hips were wide. Their hind limbs were spaced very far apart, giving them a stable base. Many titanosaurs had osteoderms, and some even had spiky armor. Titanosaurs ranged in size, but among their ranks were animals like Argentinosaurus, a sauropod that, as we learned earlier, is estimated to have weighed over 100 tons. It was 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, the Carcharodontosaurus. This group is named for the shape of their teeth, which resemble those of Carcharodon, the great white shark. Carcharodontosaurs a type of Allosauroids. So they are descendents of those big theropods that first rose to prominence in the late Jurassic period. However, Carcharodontosaurs differed from older Allosauroids in a number of ways. Most noticeably, Carcharodontosaurs have bigger heads with longer jaws. Some paleontologists speculate that to attack titanosaurs, carchardontasaurs used their mouths for more than simple biting. With strong muscles connecting their heads to their necks, these sharked toothed dinosaurs may have opened their jaws wide agape and swung their entire heads in a downward arc against the sauropod's flank. Using this motion, the upper jaws would have acted like giant meat cleavers, slicing off huge chunks of flesh. As late Cretaceous Titanosaurs got bigger, so did Carachardontosaurs. The largest of all was a South American Giganotosaurus. And I have the lower jaw of one of them here. At over 13 meters in length, Giganotosaurus was larger than Tyrannosaurus Rex. There was room for more than one kind of big carnivore in the late Cretaceous of South America. This is a skull of Carnitorous. Carnitourus is an abelisaur. An Abelisaurs grew to over 10 meters long, and were the last survivors of the Coelurosaur lineage. In the Cretaceous period, this group was strictly limited to Gondwana, but they thrived there, as Abelisaur fossils have been found throughout the southern hemisphere. Living alongside Carcharodontosaurus must've been tough. And the need for ecological niche partitioning drove Abelisaurus to adapt a strikingly different morphology. While Carcharodontosaurus have long jaws with big teeth, Abelisaurus have short muzzles and proportionately tiny teeth. While carcharodontosaurs tended to have powerful forearms with large hooked claws, Abelisaur had ridiculously short stubby arms with small claws. And while Carcharodontosaurs liked to prey on huge titanosaurs, Abilasaurs hunted the smaller species of titanosaurs and other less daunting herbivores. Carnitores shows off another trait common to most abilasaurs: a rugose, or wrinkly bone texture on the skull. They also had large cranial ornamentations. The rugocity suggest that the faces of Abelosaurs were covered with tough keratinous pads. The cranial ornamentations, which took the form of bony horns and large lumps were probably sexual display structures. It has also been suggested, in the case of Carnotaurus, that the horns might have been used in head to head shoving competitions between males over mating rights and territory. Now that we have covered the most prominent dinosaur groups in Gondwana, we can take a comparative look at Laurasian dinosaurs. At the end of the Cretaceous period, which of these dinosaur groups could be found in both Gondwana and Laurasia? More than one answer might be correct, so mark all that you think apply. A) Titanosaurs. B) Abelisaurs. C) Stegosaurus. Or D) Carcharodontosaurs. The correct answer is A, Titanosaurs. So far, no fossils from crustaceous Abelisaurs have been found in Laurasia fossil beds, and the group seems to have been limited to Gondwana. Stegosaurus are known Gondwana and Laurasia, but Stegosaurs became extinct on both land masses not long after the Cretaceous began. Carcharodontosaurs are known from the late Cretaceous of North America. But by the end of the Cretaceous they were gone. And appear to have been out competed by another group of big theropods. Although titanosaurs were more abundant and diverse in Gondwana, they were also present throughout the late Cretaceous in Laurasia. And what is now Asia, titanosaurs were important but comparatively rare components of the ecosystem. In North America, titanosaurs were much fewer in number and variety. This relative under abundance of sauropods in the north is one of the biggest differences between the late Cretaceous fauna of Laurasia and Gondwana. This means that herbivorous ecological niches were filled by other kinds of Laurasian plant eaters, and we'll meet them next. Although stegosaurs never made it to the late Cretaceous period, another group of thereophorans did. The ankylosaurs. In Laurasia, ankylosaurs split into two major groups. The ankylosaurids are the ankylosaurs with the famous tail clubs. Ankylosaurids have large backward pointing horns at the rear of the skull. And a short rounded snout in the front. Here is a skull from the second major group of Ankylosaurs. This is the Nodosaurid Edmontonia. Nodosaurids lack tail clubs, but some, including Edmontonia, had offensive weapons at the front end. In the form of large osteoderm spikes that projected outwards from over their shoulders. You can see that notosaurids did not generally have the big skull horns of anckylosaurids, and that their snouts were significantly narrower and more elongate. As you can guess, Ankylosaurs fossils include plenty of osteoderms. For many years, paleontologists were not sure how useful Ankylosaurus osteoderms were for identifying different species. Osteoderms were therefore considered to be of little taxonomic value. Recent work by University of Alberta paleontologists has shown that this is not true, and that osteoderms can be diagnostic bones. This has changed the assessments of ankylosaur species' diversity, and has made it clear that throughout Cretaceous Laurasia, the armored dinosaurs were a bigger part of the ecosystem than previously realized. Thinking back to camptosaurus, you remember that the Iguanodon Ornithopods had originated in the Jurassic period. During early Cretaceous, Iguanodons thrived and became common across the globe. In Laurasia, a new kind of Iguanodon evolved, 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. The success of the duck-billed dinosaurs was thanks in large part to their sophisticated dental batteries, which let them chew through Mesozoic plants like never before. Hadrosaurs were most abundant in Laurasia but the group did manage to spread to Gondwana. Hadrosaur fossils have even been found as far south as Antarctica. Among advanced Hadrosaurs, there are two major groups. This is corythosaurus. It belongs to the lambeosaurean hadrosaurs. Lambeosaureans are the hollow crest hadrosaurs. The bg crest you can see on its head can be thought of as a kind of horn. Not a horn like the face of a rhinoceros or triceratops, rather a horn as in a musical instrument. Inside the 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 Lambeosauruns came in a variety of sizes and shapes. This not only gave each species a unique appearance but a unique sound. Studies of Hadrosaurs ears indicate that the group had excellent hearing. Like the unique calls and songs of modern birds, the species specific sounds that Hadrosaurs generated with their cranial instruments could have been used to court mates, establish territories, or communicate a variety of messages to members of their own kind. The second major group of hydrasaurus is called the Hadrosaurines, or some times the Saurolofeins. Hadrosaurines are classically referred to as the crestless Hadrosaurines, or because some Hadrosaurine skulls do have small projections and ridges sometimes as the little-crested hadrosaurians. But a recent discovery by University of Alberta researchers has proven that neither of those names is appropriate. Although hadrosaurines do not have the complex sound-amplifying crests of the lambiasaurines, some Hadrosaurines still had large crests, they just were not made of bone. This is a piece of an extraordinary Edmontosaurus mummy specimen found near the city of Grand Prairie Alberta. Edmontosaurus is a Hadrosaurine hadrosaur, which was presumed for years to have been completely crestless. You’ll recall from the previous lessons that a dinosaur mummy is specimen that includes fossilized skin that is still clinged to its end life position. Here you can see a large section of skin from the edmontosaurus curved neck. These wrinkles preserve the natural folds that the skin had when it was fossilized. These large oval shapes are a 3D pattern in the skin, similar to the hide of an Indian Rhinoceros. If you look closely, you can see the tile pattern of the individual scales that cover the skin. Now here's the really exciting part. These are the bones from the right side of the Edmontosaurus' face. The snout and big duck bill would be sticking out this way. This is the top of the Edmontosaurus' head. Look at this big lump sitting on the scalp. Here, you can see the same pattern of small scales. This lump is actually a fleshy crest, similar to the comb of a modern rooster. Because the crest has no bone component, and it was made of only soft tissues, the hundreds of Edmontosaurus skeletons that have been found never gave us any clues to the crest's existence. This one specimen has literally changed the face of Edmontosaurs. And has challenged what we thought we knew about the so called Crestless Hadrosaurines. Running a close second to Hadrosaurs, in terms of and success was another group of herbivorous dinosaurs, the Marginocephalians. That name literally means fringe heads, and refers to an over hanging lip of bone at the back margin of the skull. Here's the skull of a pachycephalosaurus Stegoceras. And you can see the skull fringe here. pachycephalosaurs are one of the two major groups within the Marginocephalians. The other group is these Ceratopsians. The first ceratopsians were a far cry from the later and famous forms like triceratops. Primitive ceratopsians like Psittacosaurus were small and bipedal dinosaurs, but they still had a few family resemblances. Like all ceratopsians, they had large beaks and small cheek horns projecting from the side of the face. Psittacosaurus and other primitive ceratopsians are abundant in Asia. However, the larger advanced ceratopsids like triceratops are known only from North America. This kind of diversity within Laurasia was possible during the lateCretaceous period because at this time the continent was beginning to break apart. The Coelosaurs came a long way from the small and humble forms we met in the Jurassic period. By the late cretaceous, Coelosaurs had blossomed into the most diverse of all Theropod groups. These are Ornithomimid. A kind of Coelosaur that evolves a body plan similar to that of a modern ostrich or but with long clawed four limbs and a large tail. LIke ostriches, ornithomimids had beaks, long legs for fast sprinting, and were probably mostly herbivores. Another group of Coelosaurs developed a highly specialized wrist bone called a semilunate carpel. These crescent shaped bones allowed the hands to be folded backwards at a sharp angle. And the dinosaurs that possessed them are called maniraptorans. Birds are one group of maniraptorans. And the semilunic carpals of birds allowed them to delicately fold their wings when not flying. As close relatives of birds, the sickle-clawed romeosaurs are also manoraptors, and here's another; this is an oviraptor. Like ornithomimids, oviraptorosaurs were a group of theropods that adapted to a mostly vegetarian diet, and lost their teeth in favor of large beaks. Many oviraptorsaurs had cranial crests and fans of feathers at the ends of their tails. This is a cast of a fossil claw that was once responsible for considerable confusion. When it was first found, paleontologists had no particular reason to think that it belonged to a dinosaur. It certainly did not look like the claw of any dinosaur that had ever been found before. Instead, it was mistaken for the claw of a giant turtle. In actuality, it is the claw of a Therizinosaur. In this section of the course, we've encountered many strange looking dinosaurs, but the Therizinosaurs may well be the strangest. Like a sauropodimorph, a therizinosaur has a small skull on the end of a long neck, and hind feet with four forward pointing toes. Like an ornothician, a therizinosaur has a backwards directed pubis and jaws with small herbivorous teeth in the back and a beak in the front. The also have short tails and long arms with three fingers, each wielding one of these huge claws. As it turns out, therizinosaurs are not sauropodimorphs or ornothicians. They're close relatives of overaptorosaurs, and our maniraptoran theropods with the semilunic carpels to prove it. Here is a tricky question that will put your anatomical reasoning to the test. Which of the following do paleontologists consider to have been a common part of a Therizinosaur's diet? Is it:- A) Plants. B) Fish. C) Insects. D) Seaweed. Or E) No one can be sure. More than one answer might be correct, so mark all that apply. This is a controversial topic. No one is really sure what Therizonosaurs ate, and different paleontologists have different hypotheses. If you asked Scott Persons, he'd say that the short beaks, teeth and backwards pubic bones of Therizinosaurs indicate a mostly herbivorous diet, and those wicked claws were needed for defense. If you asked Dr. Curry, he would speculate that the long arms and claws of Therizinosaurs were adaptations for spearing fish. Some other paleontologists think of Therizinosaurs as giant anteaters that specialize in an insectivorous diet, and use their claws for tearing into termite mounds and ant hills. But we can all agree that Therizinosaurs were not specialized seaweed eaters. However, this notion isn't as off the wall as it sounds. It is actually the first speculation on therizinosaur diet that was ever put forward, back when they were thought to be giant aquatic turtles. In any event, E is the correct answer. No consideration of the late Cretaceous fauna of Laurasia would be complete without discussing one final group of coelurosaurs. They were close relatives of the ornithomimads, were likely among the most social of all Mesozoic therapods. Have been estimated to have had the strongest jaws in the animal kingdom, and are the most famous of all dinosaurs, the Tyrannosaurus. For much of the Cretaceous, the allosauroids had filled the niche of the top predator throughout Laurasia, just as they did in Gondwana. As coelurosaurs, the tyrannosaurs did not inherit their position as alpha predators from their ancestral lineage. Rather, they ousted the allosauroids, just as the allosauroids had ousted the large megalosaurides and ceratosaurides back in the Jurassic period. To some extent, tyrannosaurus achieve their success by taking to a further extreme, the same adaptations that had once set the Allosaurloids apart from their competitors. That is, they evolved longer legs and a much stiffer vertebral column. However, tyrannosaurs also evolved the thick, bone crushing teeth we discussed earlier in this course. Tyrannosaurs also evolved massive skulls with tremendous jaw muscles. The earliest tyrannosauroids, like the Asian species, Dailong and Guanglong. 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. Those 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. Which of the following coelurosaurs are known only from Laurasia. A) Tyrannosaurs. B) Ornithomidis. C) Therizinosaurs. Or D) Oviraptorosaurs. More than one answer might be correct, so mark all the answers that you think apply. For now, Tyrannosaurs, Ornithomidis, Therizinosaurs, and Oviraptorosaurs are all known uniquely from Laurasia. So all four answers are correct, although, close relatives of ornithomidis have been found in Africa. This may change as the fossil record improves. After all, even if a species evolved in isolation on one continent, it did not have to stay there. It should be remembered that the movement of the continents does not always lead to geographic isolation and evolutionary diversification. Sometimes, continents drift together, not apart. When that happens, species from one land mass can spread to the other. This can lead to very similar flora and fauna appearing in both locations. For instance, during the late Cretaceous, there is good evidence of a direct land connection between Northwestern North America and East Asia. Dinosaur species discovered here in Alberta have very close cousins in the late Cretaceous beds of Mongolia's Gobi desert. When plate tectonics bring land masses together and animals move between them, we call this phenomenon a faunal interchange. That brings this lesson's trip through the evolutionary history of dinosaurs to a close. But we're still missing two parts of the story. The beginning and the end. In the next lesson, we'll take a look at how dinosaur evolution got started in the first place
