Après l'extinction des dinosaures, les mammifères sont devenus 1 000 fois plus grands, et voici pourquoi. Avec la disparition des dinosaures, il y avait beaucoup plus d'espace et de nourriture disponibles pour les mammifères survivants. Cela leur a permis de grandir davantage et de prendre les rôles écologiques que les énormes dinosaures occupaient. Les mammifères plus grands pouvaient mieux se défendre, explorer de nouveaux environnements et trouver diverses sources de nourriture. De plus, le climat et les habitats favorisaient ces grands mammifères, conduisant aux géants que nous voyons dans les archives fossiles. Animation créée par Sympa.
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FunTranscript
00:00Bam, a giant asteroid crashed on Earth and shortly after, the dinosaurs disappeared.
00:14We could think that there was nothing to be afraid of after that, but no.
00:18Unique and frightening creatures began to evolve.
00:21At that time, the mammals crossed significant lines of the Earth.
00:28And it seems that some of them, similar to horses and rhinos,
00:32must have become very quickly gigantic after the disappearance of the dinosaurs.
00:38At the time when they reigned, about 66 to 145 million years ago,
00:44mammals were relatively small creatures,
00:47who often lived in the shadow of their formidable predators to avoid being devoured.
00:51Many did not weigh more than 10 kg, or even much less than that.
00:57However, after the disappearance of the dinosaurs,
01:00mammals finally had the opportunity to be part of this new environment.
01:04Like the Brontotheridae, for example, who seized their chance to reach gigantic sizes.
01:09With an initial weight of about 18 kg,
01:12they ended up weighing between 4 and 5 tons in just 16 million years.
01:16It may seem long, but it is relatively short in terms of evolution.
01:20And this great size gave them, as well as other mammals,
01:25a decisive advantage after the disappearance of the dinosaurs,
01:29thus making them dominant and feared creatures.
01:33The Brontotheridae, of which the fossils have been discovered in North America,
01:38have received the impressive nickname of the animals of thunder from the Sioux.
01:42They thought that the fossils came from gigantic thunder horses,
01:47which once traveled the plains during storms.
01:51The mystery persists as to the speed with which these animals of thunder grew.
01:56A theory suggests that their size would have increased gradually.
02:00Another hypothesis advises that they would have experienced periods of rapid growth,
02:04followed by phases of stagnation.
02:06It is also possible that there was a mixture of species,
02:09some small and others large,
02:11but overall, most ended up becoming huge.
02:15Scientists, after studying the genealogical tree of 276 Brontotheridae,
02:20concluded that this third hypothesis was the most probable.
02:26In nature, everything is a story of competition.
02:29At that time, most mammals were small,
02:32which led to fierce competition among small herbivores for food.
02:36The largest, such as the Brontotheridae,
02:39however, had much less competition for the resources necessary for their survival.
02:43Thus, the largest species had no chance of persisting,
02:47while the smallest disappeared quickly.
02:53Indeed, the disappearance of dinosaurs did not mark the end of impressive and gigantic animals.
02:58For example, I would certainly not like to come across a Barylambda.
03:02This animal is a bit reminiscent of a giant sloth,
03:04although it evolved tens of millions of years later.
03:07This colossus lived 50 to 60 million years ago in North America.
03:11It was about 2.40 meters long
03:14and had a particularly thick and robust body and limbs.
03:18Its tail, also very heavy,
03:21probably served as support for it to stand on its hind legs.
03:24Its skull was relatively short compared to its imposing body.
03:28It is interesting to note that it still had clavicles,
03:31bones that most of the mammals have lost over the course of evolution.
03:35Fortunately, it probably fed on plants
03:38that are soft enough to be easily chewed,
03:43which makes them much less frightening.
03:48Now imagine a snake so large that it could rival a T-Rex in size.
03:52It is not a mythical creature, but the Titanoboa,
03:55a prodigious snake that lived about 60 million years ago
03:59in the lush forests and streams of South America.
04:03It is the largest snake ever discovered.
04:06It was actually the ancestor of the current Boas and Anacondas,
04:09which still live in the same region.
04:11Its body reached a stunning length of 13 meters,
04:14which is longer than a school bus.
04:16To support this gigantic body,
04:18the Titanoboa had about 250 vertebrae,
04:21these bones that give their name to vertebrate creatures.
04:24Imagine how much it had to eat to maintain this massive body of 1,200 kg,
04:29the weight of a small car.
04:32It attacked fish and crocodiles living in the waters of its habitat.
04:35A snake capable of scratching a crocodile
04:38must undoubtedly be a formidable creature.
04:41The Titanoboa currently holds the record for the largest snake,
04:45but scientists think that we could discover
04:49even larger fossils in the future.
04:53You know you had to include a scary crocodile on this list.
04:57At the time of the dinosaurs, giant crocodiles such as the Sarcosuchus
05:01and the Deinosuchus could reach up to 12 meters long
05:04and feast on dinosaurs for their meal.
05:06You can see that they have not lost anything of their terrifying look over time.
05:10This creature, the Barinasuchus,
05:12lived 15 to 55 million years earlier,
05:15in what corresponds today to Venezuela,
05:18Peru and Argentina.
05:20It belonged to a group of crocodiles, the Cebesidae,
05:23who lived alongside the dinosaurs
05:25and experienced a flourishing period after their disappearance.
05:28Unlike most crocodiles,
05:30which are content to stay in the water,
05:32this one liked to walk on the ground to explore its environment.
05:36Its flattened teeth, in the shape of blades,
05:39are more reminiscent of carnivorous dinosaurs
05:42than those of other crocodiles.
05:44This adaptation allowed it to catch prey
05:47during its quiet walks on the shore.
05:50This formidable creature could exceed 6 meters long
05:53and weigh more than 1,400 kilos,
05:55making it more imposing than today's marine crocodiles.
06:00Even the rhinoceros had an XXL size at the time
06:04that followed the dinosaurs.
06:06The latter, however, with the complicated name of Paraceraterium,
06:09was a huge herbivore
06:11that lived in the eastern part of Eurasia
06:1323 to 34 million years ago.
06:15Although it looked like a rhinoceros,
06:17it had notable differences.
06:19In particular, its neck of more than 180 meters,
06:22which gave it the appearance of a rhinoceros with the neck of a giraffe.
06:25The creature stood at more than 4.60 meters tall,
06:29surpassing most other animals of its time.
06:32Although its appearance may have seemed frail,
06:34it was actually extremely heavy,
06:36weighing 15 tons,
06:38equivalent to two or three African adult elephants,
06:41or even a small house.
06:44One of the largest carnivores to have traveled through Australia
06:47during the Ice Age was not a mammal,
06:50but a formidable reptile named Megalania.
06:53This predator could reach more than 5.50 meters long,
06:57more than double the length of the Komodo dragon,
07:00one of the largest lizards today.
07:04Megalania had sharp and curved teeth,
07:07similar to those of Komodo dragons,
07:09which gave it an extremely powerful bite
07:12and possibly venomous.
07:14This venom could prevent its prey from healing,
07:17thus weakening the animal
07:19and facilitating its capture after a first bite.
07:22And whatever the effort of the animal to escape.
07:28Now let's move on to the birds.
07:30The elephant bird, which measured nearly 3 meters high
07:32and weighed more than 450 kilograms,
07:34inhabited the island of Madagascar a little over a thousand years ago.
07:37Compared to other prehistoric creatures,
07:39it is not so old.
07:41One of these species of elephant birds,
07:43Laepionis maximus,
07:45was so imposing that it rivaled some non-avian dinosaurs,
07:48such as Lutaraptor in terms of size.
07:51Its eggs were also gigantic.
07:53One could weigh more than 9 kilos,
07:55which is much heavier than a bowling ball.
07:59The interior of its eggs offered enough space
08:02to contain more than 100 chicken eggs.
08:07Whether on land, in the air or in the water,
08:09you could never really know
08:11if these gigantic creatures were after you
08:14or after your salad.
08:16Maybe you've already heard of the Leviathan.
08:19This ancient and powerful predator
08:21was a kind of jack-o'-lantern,
08:23but much more imposing and formidable
08:25than the species we know today.
08:27While modern jack-o'-lanterns
08:29mainly fed on squid,
08:31the Leviathan's diet probably included
08:33other whales.
08:36Another large predator evolved
08:38at the same time and at the same place
08:40as the Leviathan, the famous Megalodon.
08:42Researchers estimate that it was also
08:44used to hunt whales.
08:46The competition to obtain
08:48the most appetizing prey
08:50and the clashes between these huge predators
08:52became spectacular.