Nos ancêtres et les des dinosaures ! - C'est pas sorcier [Intégrale]

Jamy, where are you ? Have you finished the genealogical tree of your cat ? Yes, and it's completely crazy ! The furthest ancestor of my cat would be a big mouse ! Don't complain, you dromedaries ! You too are mammals, like the cat, and their ancestors are probably mice too ! Come on Jamy, join me, we'll try to know more about the great history of mammals. Come on my cat, we'll try to find your great-great-grandparents. And as they say, you have to let the mammals. A riddle with three clues. Who are they ? 1. Most of them are covered in fur. 2. Their body temperature remains constant, it means that it does not depend on the time they spend outside. 3. Finally, and above all, females breastfeed their young. Answer ? Mammals ! There are about 5,000 species on Earth, including humans, and what is extraordinary, is that they colonized all environments. We find them in the air, in the oceans, in the most extreme environments. And yet, originally, when mammals appeared on Earth, their future seemed rather dark. Oh yes ! Come on Marcel, immerse us in the atmosphere ! The great history of mammals begins at the feet of the dinosaurs, who for a long time reigned as absolute masters on all Earth. Faced with these formidable conquerors, our distant ancestors have no choice but to be discreet. Like for example, come and see, Eomaya. Eomaya is the oldest complete fossil of mammals ever discovered, 125 million years old. And like most mammals of the time, it is not bigger than a mouse. Yes, some scientists think that most of these little mammals lived mainly at night. Hide, Eva ! I would like to see it in their place. Let's try to see it a little clearer. And let's start by taking a look at the calendar. This story goes back to the Mesozoic. So I know, it's not an easy word to remember, but we'll have to do it because that's how we designate the period that stretches between less than 250 and less than 65 million years, what we used to call the Secondary Era. During this period, dinosaurs reigned as masters of the living world. They occupied all the ecological niches. Oh, so there were ecological dogs as well? But no, it's a way of speaking. An ecological niche is a space in which a species feels good and finds everything it needs to feed and reproduce. So a crowd of elements comes into play. The relief, the nature of the soils, the vegetation, the brightness, the climate, with all these components, temperature, hygrometry, etc. In the Mesozoic, the Great Plains are colonized by dinosaurs. The sky is dominated by flying vertebrates, the famous pterosaurs, and the oceans by aquatic reptiles and amphibian animals. To live in such a context, mammals have no choice. They have to be as discreet as possible. Evolution selects where they are, and where they are not. of small animals and animals capable of living at night when everyone else is asleep. The oldest fossil of mammals known is this one, a complete skull dating from 220 million years ago belonging to Adilo basileus. It looked like a big muse and we think it was mainly fed by insects. Then, for millions of years, mammals have evolved. Here, this small piece of jaw belongs to Laolestes, which appeared more than 70 million years ago after Adilo basileus. It was also a kind of big insectivorous mouse. But at the time, it was the best way for mammals not to be noticed by the terrible dinosaurs they were next to. Hunting down tiny insects at night when you can't see anything, must not have been an easy task. So, mammals had to adapt. In particular, they developed a great sense of hearing thanks to tiny bones difficult to observe on this tiny head 80 million years old. Jamy, do you see anything? Not much, no. Here are the tiny bones Sabine is talking about. There are three of them, the hammer, the anvil and the mace. Only mammals have them. These are the smallest bones of the skeleton. Look, there are two here, a hammer and an anvil of human beings. So, what advantages do they have for night life? Well, sound is air that vibrates. Vibration goes through the auditory duct and makes the tympanum vibrate. The three small bones that are just behind amplify these vibrations which then spread to the inner ear where they are transformed into electrical signals which are then directed to the brain. Well, thanks to these bones the first mammals perceived frequencies which other animals were not sensitive to which allowed them to locate their prey more easily, insects in particular. But that's not all. To process this information, the mammal's brain gradually developed. Here is a dinosaur brain, a stegosaur precisely. It is an archaic brain which only controls the primitive functions of the organism such as breathing and reproduction. Mammals, humans in particular, always have this archaic brain, this reptilian brain. Only, over time, it became enriched with an envelope, the neocortex. It is also perfectly visible in the mouse. Here, the reptilian brain and all around the neocortex. Well, it is in this area that sound information is processed. Being able to better process this sound information, mammals were therefore the best adapted to nocturnal life. Thanks to their exceptional hearing, mammals became masters in the art of spotting their prey in the dark. And hop! Insects are very rich in calories. They therefore represented a food very adapted to the neocortex of mammals which needs a lot of energy to function. Their teeth also specialized over the generations to break the shells more easily. But all the mammals of the time were not so small. This skeleton of the size of a calf is that of Repenomamus who lived 130 million years ago. An exceptional mammal because we found in his stomach remains of baby dinosaurs, in particular Psittacosaurus. And yes, he dared to come to life to hunt them but watch out for him if he came upon his parents. If nothing had come to interrupt the reign of dinosaurs, we might not be here to talk about it. Only here an extraordinary disaster occurred 65 million years ago and I have the means, Jamy, to make you relive this great moment. Oh no! Here, sequence mega volcanic eruption. Yes, I know, you're having fun. Nevertheless, it must have been funny for everyone. About 65 million years ago, the volcanoes located on the plateau of the Deccan in India, India, which does not occupy its current position, well, these volcanoes erupted. This geological phenomenon lasted for 100,000 years. During this period, the volcanoes spat out thick smoke that polluted the atmosphere and caused acid rains. Hey Jamy, next sequence. Oh no! Mega meteorite. Not the meteorite, it's going to rot. Jamy, are you still there? Of course, I'm still here. I haven't disappeared. This meteorite crashed in Mexico. The shock is at the origin of a gigantic cloud of dust. The combination of the two, volcano plus meteorite, has probably plunged the Earth into the cold and darkness for several hundred years. 75% of the species did not survive. The dinosaurs in the lead. Their disappearance will free ecological niches which will soon be occupied by mammals which, although affected, have generally better resisted this cataclysm. This crisis marks the end of the secondary era and the beginning of the tertiary era. And now, it's over for the dinosaurs. Well, the place is now free for mammals. Yes, but Sabine, you still forgot to say that not all dinosaurs have disappeared. Some have become very familiar animals. When you give seeds to the pigeons or when your children give small pieces of bread to the pigeons in the garden of plants, well, they feed on dinosaurs. The birds are actually dinosaurs. And these are dinosaurs which, about 140 million years ago, that is, a long time before the extinction of the end of the Cretaceous, acquired feathers and not only acquired feathers but also acquired a beaten flight. These dinosaurs gave birth to this group of birds which is completely included in the dinosaurs. But the disappearance of all the other dinosaurs has left the field open to mammals which have finally been able to multiply and diversify. At the very beginning of the Tertiary Era, we know some, we know mammals, we know groups very different from what we knew in the Cretaceous. For example, here you have a small mammal skeleton which comes from Bolivia, from the central Andes of Bolivia which is about 64 million years old. It belongs to a group called the Pantodons. And this fossil is an absolutely exceptional specimen. Look at the quality of preservation of its skull. We can see that all the teeth are preserved. It is all the more exceptional because it was a female and she was still carrying her baby, a fetus, close to term, whose skull we can see here. Later, the family of this fossil evolved towards much larger animals like this Pantodon herbivore the size of a tiger which lived 55 million years ago. This corresponds to the moment when the diversity of mammals really began to explode. We are now in Germany, not far from Frankfurt on the site of the Messell excavation. An absolutely fabulous site to such an extent that UNESCO has inscribed it on the list of world heritage. Thank you. What makes this site fabulous is its exceptional wealth in fossils. Old fossils of 47 million years old. A site that testifies to what scientists call the radiation of mammals. And Thomas, can you tell us what radiation is? Mammals at this time, after the extinction of dinosaurs, began to have a lot of adaptations to different environments, to different lifestyles, to different locomotions. And so we can find in these blocks and stuck between the different layers, we find fossils. But when I say we find fossils, here we find them by thousands, but really by thousands. It sounds incredible but I assure you it's true. These fossils are trapped in bituminous schist, an oily rock that breaks easily. It is enough with a knife. By the way, look, Martin, the head of the excavators, has just found a pretty leaf. Do you realize? An old leaf of 47 million years old. But you have to quickly plunge it into the water because these fossils degrade very quickly in the open air. Then, let's go to the laboratory. And there, I think I know that Sabine and Thomas have reserved a little surprise for us. Leptictidium. So here it is, well sheltered to prevent it from drying out. Here we see a very, very long tail, almost as long as its body, and therefore very, very long hind legs. Its head, does it have something, its head? Its head, it has a slightly elongated muzzle, but above all it has very pointy teeth to eat insects, but also animals. So it was probably a mammal that bounced like a kangaroo that ate other animals. Wow. Only now, there is still a lot of work before extracting it from its stone ganglion. The archaeologists of Messel have developed an original method to preserve fossils. The apparent side is first carefully cleaned and updated. Then, it is covered with a thick layer of resin. After a long drying, the fossil will be turned over and the excess of resin removed so that the skeleton appears in relief. But these fossils are extremely flattened because they formed in very particular conditions at the bottom of a lake born as a result of a volcanic explosion. The Messel Marl Lake was a big lake at the bottom of which there was no oxygen. So, on the bottom of the lake, you had two possibilities that the carcasses and subranines which fall to the lake fall down and don't decay. So, in the end, the concrete skeletons were preserved but when they fall down on the bottom of the lake, the next layers of sediment will happen. So, you have a high pressure of sediment which presses the fossils together and they are very flat. Until now, we have found in Messel no less than 400 species of plants, 400 species of insects, dozens of species of fish, reptiles and birds and 150 species of mammals. Once the preparation is finished, here is the result. Come on, with delicacy please. This is Leptictidium, the same as the one we have just discovered on the excavation site. And now, look, you understand why Messel is so famous. It's because there are no isolated fossil fragments but complete skeletons perfectly positioned. The soft tissues themselves are preserved. Look here, the stomach of the animal and its content. And that's not all. Messel is also famous for the quantity and diversity of animals, of mammals in particular that we have discovered. Look here, for example, at its dentition, we recognize a rodent, a kind of rat which, we think, was able to swim. And here, a representative of the oldest family of artiodactyls, the family of deer, goats, cows, giraffes. It's beautiful. And here, here, it's the oldest pangolin ever discovered, 47 million years old. What does a pangolin The little voice of a pangolin, the amateur of ants, termites. Look, its back, front, back, back, etc. grandfather was already equipped with terrible claws to dig the ants, but he didn't have useless teeth to swallow the ants that were found inside his stomach. So what we learn at Messel is that shortly after the extinction of the dinosaurs, about 20 million years ago, the mammals already occupied all the ecological niches. Not bad! It's very fast. So why so many different species in such a short time? Well, first of all, because they have the free field. The dinosaurs having disappeared, the ecological niches are now available. But what also explains this great variety of species is that the first mammals had a rather high rate of reproduction, a bit like mice. These animals, in fact, reach their sexual maturity after a few months. In a year, a female can make 9 out of 10 babies, that is, 90 descendants. Among which, the females will be just as fertile, giving birth 1,000 grandchildren, who will follow the same path and give birth to about 700 great-grandchildren. In short, in a year, a mouse can have about 1,800 descendants. However, the more births and generations there are, the more genetic mutations there are, and the more these mutations have a chance to be advantageous and therefore to persist. Thus, from mutation to mutation over 20 million years, we went from the ancestors of rodents to the ancestors of felines, to the ancestors of giraffes, pigs and cows, to those of horses, or even to the ancestors of whales. So many species that have colonized the niches left vacant by dinosaurs. All these species appeared in a tropical climate that reigned over a large part of the globe, especially in Europe. This impressive amphibian mammal is Ambulocetus, the ancestor of cetaceans. And this one is Leptictidium, whose fossil Sabine showed us. This mammal was a very agile who had to face enemies like the terrible Gasturnis, a giant bird 2 meters high, the largest predator of the time. The mammals had even conquered the air. We discovered in Messelles the fossils of this species of bat. To study them in the smallest detail, researchers radiograph them and obtain 3D images. By analysing the size of their internal ears, they discovered that in Messelles, some bats were already equipped with an ultrasonic that allowed them to locate their prey like in today's bats. Sabine, what are you doing in this showcase? Actually, I'm in an impasse, a garage lane, an evolutionary bag ass. What do you mean? Well, thanks to the discoveries made here in Messelles, we realise that sometimes nature opens up paths that lead to nothing. What we have in front of us, for example, are the extracts of a collection that we are very proud of. A collection of small angulets, a kind of small archaic horses, because, look, on this reconstruction, they still have one, two, three, four nails at the end of each front leg and one, two, three nails at the end of each rear leg, while the current horses have only one nail at the end of each front leg. And then, look, these fossils are so well preserved, you see all these details, that we can still see inside this female the bones of her fetus, of her baby horse, whose head is hidden by the bone of the hip. And even stronger, look at this sample, the spine is missing, but we can see here the head of the baby horse and, more precisely, its teeth, its very small teeth. Wow! Only, here, these animals are not the ancestors of our current horses. The line of the pro-paleothers has completely disappeared. Jamy, do you know what happened to them? They had a good life, didn't they? It's true that he looks cute. Let's go back to the story. The Maecel horse is the descendant of the Iracotherium, an animal that lived on the American continent. 60 million years ago, in favor of a climatic cooling that caused a decrease in the level of the oceans, Iracotherium herds probably crossed the Bering Strait to settle in Europe, in Germany, in particular. This animal found here an ecological niche. As it evolved, it gave birth to the Maecel horse, also known as pro-paleotherium. Only, the evolution stopped there. Did it fall under the assault of a predator? Did it find itself in competition with another animal? Still, the line stopped there. In America, however, Iracotherium gave birth to Mesoippus, which gave birth to Merichippus, then Plioippus, which gave birth to Ecus, the scientific name of our current horses. The little horses that disappeared from Maecel did not measure more than 60 cm in height and mainly fed on fruit and leaves. And they too were one of the favorite prey of the predatory bird Gasturnis. Like these horses, most of the mammals discovered in Maecel belong to groups that have now disappeared. This is the case of this magnificent Copicodon which had a long, fluffy tail. Its bone-like claws indicate that it was a very good climber, probably to go and get fruit in the trees. And this is Eurotamandua, an ant of 90 cm, toothless and with a pipe-shaped muzzle that housed its long tongue. Runners, swimmers, climbers, searchers, even if many species then disappeared. 47 million years ago, nature had already experimented all possible functions in mammals. I assure you! No, but it's incredible, Thomas! Look for yourself! Hey, what's incredible? Thomas is trying to make me believe that they found marsupials here in Maecel in the heart of Germany. You mean the same family as kangaroos found in Australia? Exactly! No, but honestly, what tells me that this fossil is a marsupial? Well, I did a x-ray. We can see the canines very well here. Look at the incisors. How many do you count? I count one, two, three, four on one side, one, two, three, four on the other. Oh, there are eight incisors only on the lower jaw. That's a lot. I only have four. Yes, such a large number can only be a marsupial. Oh, okay! A marsupial in Europe! Well, Janine, what a discovery! Yes, they must have found a niche and jumped on the occasion, if I dare say so. Since then, of course, they have disappeared from Europe. Anyway, they are part of the mammal class. Let's go back. Mammals are tetrapod vertebrates. In other words, they have two pairs of limbs. They are also distinguished from other animals because females breastfeed their young and because their internal temperature is constant. Another distinction, the baby's gestation takes place in a bag filled with liquid, amniotic liquid. That's it for the common points. Besides that, mammals form three distinct groups. First, marsupials. The main peculiarity, females lay a few centimeters in their womb where it will complete its growth. It's the fate of kangaroos, koalas and other opossums. Second group, mammals monotremes. There are very few of them. They are mammals that lay eggs but breastfeed their young. The ornithorynx is their flag bearer. Finally, third group, placentaries. It's the most important group to which we belong just like the cetaceans or the ruminants. They take their name from the placenta, this organ that connects the embryo to the mother and allows to feed the baby during all gestation. Jamy, come and see. I'm in front of a primate. Oh, that's nice. No, not you. Him. Notarctus, an old primate of 50 million years, an ancestor of our current Lemurians. And like all primates, look, he has a hand equipped with an opposite thumb, a hand that works like a clamp. And if it interests us so much, it's because we humans are primates too. About 50 million years ago, forests were already populated by primates that looked like big Lemurians. And once again, it was in Messel that the fossil of the most exceptionally conserved primate was discovered, named Ida. It is spread on two plates that scientists were able to virtually gather to reconstruct the animal. Ida has aroused intense debate because some researchers have claimed that it would be the direct ancestor of man. But today, we think that it belongs to a missing group, the Adapidae. Paleontologists are therefore always looking for this famous missing genome, the oldest primate at the origin of the human line. So, how do you find them, your cousins? Jamy, would you like to go and see what happened 150 million years ago during the Diplodocus? Oh no! Hey Marcel, what's going on? What's going on, Marcel? Oh, and he's looking at me in a funny way! Marcel, Marcel, don't leave me! Don't leave me! It's not you, the door! It's not you! Oh, Jamy, you're really too cute like that! You want to know more about this show and access many bonuses? Go to france3.fr, heading C'est pas sortié!