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.
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