La plus grande créature marine de tous les temps a récemment été découverte, mais au milieu d'un désert au Pérou ! Les scientifiques ont trouvé les restes fossilisés d'une baleine ancienne, que l'on croit avoir vécu il y a plus de 30 millions d'années. Cette créature massive, appelée Perucetus colossus, aurait pu peser jusqu'à 200 tonnes, rivalisant ou même dépassant les baleines bleues d'aujourd'hui. La trouver dans un désert est incroyable, mais à son époque, cette zone était sous l'eau, faisant partie d'un océan préhistorique. Ses os étaient si denses et lourds que les chercheurs pensent qu'elle était peut-être une nageuse lente, passant la plupart de son temps à flotter et à se nourrir. Cette découverte réécrit ce que nous savons sur la vie marine ancienne et la taille gigantesque que les créatures pouvaient atteindre ! Animation créée par Sympa.
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00:00A fascinating and at least unexpected discovery emerged among the rocks of the Dika Valley, in Peru.
00:07The bones of a prehistoric whale, Perusetius Colossus, which lived nearly 40 million years ago.
00:14Initially, these massive bones and unusual shapes did not arouse much interest,
00:19because they were thought to be simple gigantic rocks.
00:22Of course, this hypothesis could be intriguing,
00:25but things took a different turn when researchers realized
00:28that they were facing the remains of a colossal marine animal that once roamed the coasts of Peru.
00:33In addition, this whale would probably be the heaviest being to have ever existed.
00:38Sorry, blue whale, we know you did everything to get your place at the top.
00:42With a length of more than 30 meters and a weight exceeding 200 tons,
00:47it deserves its status as the largest animal on the planet.
00:50However, it seems that its reign is coming to an end.
00:53It is time to give the title to a new challenger, and this one is truly titanic.
00:59This creature of the oceans was undoubtedly shorter than the blue whale,
01:03but much heavier, with a mass estimated between 93 and 370 tons.
01:09If calculations point to the upper fork,
01:12Perusetius could become the largest animal ever known on Earth.
01:16This impressive weight is explained by extraordinarily dense and thick bones,
01:21a trait that is still observed today in species such as the lamentans or some of the first cetaceans.
01:26These dense bones are a considerable asset for marine mammals,
01:30because they allow them to remain submerged most of the time.
01:34But an excess of weight can be problematic.
01:36A body too heavy would tend to sink permanently,
01:39forcing the animal to spend a considerable amount of energy to go back to the surface.
01:44To avoid this, marine mammals must have sufficiently lighter tissues,
01:49such as muscles or fat,
01:51to guarantee their buoyancy while minimizing their efforts.
01:55Scientists do not have a complete skeleton,
01:57which complicates the evaluation of the size of the animal.
02:00However, they used the ratio between heavy bones and lighter tissues
02:05observed in other marine mammals to estimate the total weight of this huge prehistoric whale.
02:10These fossils were discovered about 13 years ago,
02:13and researchers spent the next 10 years extracting the whale from the rock.
02:17The analysis of its anatomy and age revealed that it was related to the basilosaurus,
02:23a whale with a long muzzle filled with sharp teeth,
02:26and an elongated body, evoking that of a eel.
02:29Even if Perusetus was not larger than the blue whale,
02:32it was no less than a giant reigning over ocean depths.
02:36Contrary to modern whales,
02:38it is plausible that this creature was a predator attacking large prey.
02:44This discovery also upsets our understanding of the evolution of whales.
02:48Researchers previously thought that these majestic creatures
02:51had reached impressive sizes about 5 million years ago
02:55when they began to consume a large amount of small prey.
02:58However, here is the proof that gigantic whales existed long before.
03:03However, it remains to be clarified how this whale found enough food to meet its needs.
03:09In addition, it remains difficult to determine precisely the diet of this ancient creature.
03:15With its imposing size and its slow swimming,
03:17it was probably looking for its food in shallow waters.
03:21It was probably feeding on crustaceans,
03:23swamps or other small animals buried in the sand.
03:26A hypothesis suggests that it was a carnivore,
03:29feeding on the remains of animals found on its way.
03:32It is not uncommon to discover fossils of marine animals in the deserts,
03:36because many of these areas were once submerged.
03:39The Sahara, for example, was, 50 to 100 million years ago,
03:44a shallow sea called the Trans-Saharan Maritime Way.
03:48If this region is now arid,
03:50the inhabitants of these places were aware of their aquatic past,
03:53because they often found old shells there.
03:56The sea reached a depth of about 50 meters,
03:59an ideal depth for swimming.
04:02Some could compare this region to today's Puerto Rico,
04:05with its abundance of sun and its shallow waters.
04:09The mangrove forests were widespread there,
04:12just like the seabed covered with molluscs,
04:14such as snails and squirrels.
04:17The marine sediments deposited after the drying of the sea
04:20are full of varied fossils.
04:22The creatures inhabiting this ancient underwater world
04:25had a less engaging appearance
04:27and were much more imposing than their current descendants.
04:30A normal-sized human being
04:32would hardly constitute an anchor for these giants,
04:35far from a complete meal.
04:37Generally, when an animal settles on a small island,
04:40it can reach a size much larger than that of its continental peers.
04:44This phenomenon, known as insular gigantism,
04:48is explained by the increased presence of resources
04:51or the reduction of the number of predators on the islands.
04:54Perhaps a similar phenomenon occurred in the Trans-Saharan Maritime Way.
04:58Although it is not an island,
05:00the incessant movements of the waters
05:02have formed small, isolated pockets.
05:04The specific conditions prevailing there
05:06have probably favored the growth of certain species.
05:10Thus, we find creatures such as sea snakes
05:13and colossal cichlids,
05:15as well as other fish that have disappeared today.
05:17Among them, a pycnodontiform was distinguished
05:20by its powerful jaws,
05:22which it used to crush shells
05:24and attack hard prey.
05:26The identity of these animals
05:28testifies to their role as predators in this ecosystem.
05:31Their diet has evolved over time,
05:33like some modern piranhas.
05:36But the competition to dominate the food chain was fierce,
05:39especially against predators of size
05:41such as sharks, crocodiles
05:43or even ancient ancestors of elephants.
05:46The Sahara has gone through several phases in its history.
05:49If you had a time machine
05:51and you visited what is now
05:53the largest hot desert in the world,
05:55as it was about 6,000 years ago,
05:57you would not be confronted
05:59with a sea of burning sand.
06:01On the contrary, you could enjoy
06:03a pleasant walk through a luxurious landscape.
06:06The inhabitants of this region, in the past,
06:08did not leave any paint on the walls of the caves
06:11depicting camels, dunes or scorpions,
06:14these characteristic elements of the current Sahara.
06:17Instead, they drew crocodiles.
06:20These illustrations offer additional proof
06:23that at one time, the Sahara was full of water and vegetation,
06:26enough to accommodate these imposing and formidable reptiles.
06:30About 3 billion years ago,
06:33the earth was probably almost entirely covered with water.
06:36Today, the oceans cover about 71% of the earth's surface,
06:41but it seems that at that time,
06:43it looked like a vast oceanic world,
06:45without a real continent,
06:47only sprinkled with a few islands.
06:49Scientists have examined particular rocks
06:52in Western Australia,
06:54formed in a deeply submerged environment
06:57called a hydrothermal source system.
07:00To better understand,
07:02it is necessary to mention two types of current oxygen,
07:04O-16 and O-18.
07:07The latter, heavier thanks to its additional neutrons,
07:10evaporates less easily.
07:12By analyzing old marine foundations,
07:14researchers have discovered a significant proportion of O-18,
07:18much higher than those observed in the current oceans.
07:21This has led them to conclude that in the past,
07:24the earth had fewer emerging lands than today.
07:27Australia, once a green place
07:29home to large animals and vast tropical forests,
07:32is today the ideal place to conduct this type of study.
07:36Over time, this land has become more arid,
07:39and deserts such as the Great Victoria Desert have formed.
07:42Tropical forests, on the other hand,
07:44have gradually reduced to the ends of the continent.
07:48This phenomenon, known as desertification,
07:51occurs when lands formerly fertile
07:54and adapted to agriculture
07:56turn into deserts.
07:58If natural climate change contributes to this evolution,
08:02human activities, such as mining,
08:05intensive agriculture or urban construction,
08:08also play an important role in this transformation.
08:12When lands become desert,
08:14this poses many problems.
08:16They can no longer produce food,
08:18drinking water becomes insufficient,
08:21and animals lose their natural habitat.
08:24To fight this phenomenon,
08:26many countries have adopted a plan.
08:28This aims to collaborate with farmers
08:30to restore degraded lands,
08:32manage water more efficiently
08:34and preserve productive areas
08:36in order to improve living conditions on our planet.