Il y a environ 128 millions d'années, les serpents ont connu un boom d'adaptation significatif, les amenant à évoluer jusqu'à trois fois plus rapidement que les lézards. Initialement, lorsque les serpents ont évolué à partir des lézards il y a plus de 100 millions d'années, ils étaient des acteurs mineurs dans des écosystèmes dominés par les dinosaures. Aujourd'hui, il existe environ 4 000 espèces de serpents, allant des énormes anacondas verts aux minuscules serpents-fil. Sur les 25 groupes de lézards sans pattes, seuls les serpents se sont véritablement diversifiés et ont prospéré. Une étude récente met en lumière les raisons de ce fascinant succès évolutif. Animation créée par Sympa.
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FunTranscript
00:00About 128 million years ago, snakes suddenly appeared and began to thrive on Earth,
00:07ending up diversifying into a few 4,000 species that we know today.
00:11Nevertheless, it is not only by losing their members and adopting a long and serpentine form that they succeeded.
00:18Although there are 25 groups of lizard without members, it is the snakes that have truly won the palm in terms of diversity.
00:26To understand what makes snakes so efficient, scientists have studied more than 60,000 reptile specimens from museums around the world.
00:35According to them, snakes would have evolved faster than lizards in key areas,
00:40offering them an advantage to exploit new opportunities.
00:44If you find this frightening, I fully agree with you.
00:47But let's continue.
00:50A major factor in their success lies in their eating habits.
00:55With their flexible skull and their sharp sense of smell,
00:58snakes can ingest prey larger than their heads and track their victims like pros.
01:04When dinosaurs disappeared, about 66 million years ago,
01:08snakes were about to adapt to this changing world and occupy vacant niches.
01:13Although we are not sure why snakes evolve so fast,
01:18it is obvious that they represent a singularity in the great curve of evolution.
01:22Just like the sudden explosion of flowering plants,
01:25these macro-evolving singularities have shaped life on our planet in an unexpected way.
01:30Today, snakes are present almost everywhere on Earth, exhibiting a wide variety of characteristics and habitats.
01:37They are found in deserts, tropical forests, meadows and even in the depths of the oceans.
01:44All snakes are predators, feeding on various prey,
01:48including insects, small vertebrates, other snakes and sometimes even large mammals, even humans.
01:57However, you will not see any snakes in Ireland.
02:00Why?
02:01One of the most famous legends says that St. Patrick would have hunted his reptiles from the island.
02:06However, experts believe that snakes never inhabited Ireland at first,
02:11making this story a symbol rather than a reality.
02:15There are also other regions of the world where snakes are absent,
02:19such as Iceland, Greenland, New Zealand and Antarctica.
02:23The absence of snakes in New Zealand is particularly intriguing,
02:26given its proximity to Australia, where snakes abound.
02:30The reason for this absence seems to be the constantly changing climate of the country,
02:34making the survival of snakes difficult.
02:37Although New Zealand is devoid of terrestrial snakes,
02:40it sometimes happens that sea snakes visit its waters.
02:43The black and yellow sea snake and the yellow-lip striped tricot are known to visit the island from time to time.
02:52As for the country with the largest number of snakes, Brazil wins the palm.
02:57With more than 375 species, it has an assortment of harmless and dangerous snakes.
03:03The vast tropical forests of the country offer an ideal habitat for these reptiles,
03:08including famous constrictors such as Anaconda, Boa Constrictor and Boa Emeraude.
03:14Brazil is also home to venomous snakes such as spearhead and coral snake.
03:20However, if you are afraid to participate in the carnival in Rio because of the fear of Brazilian snakes,
03:25know this.
03:26Of the 4,000 species of snakes in the world, only about 600 are venomous
03:31and about 200 are capable of harming us.
03:34The bites of deadly snakes are therefore less frequent than one might think.
03:38The chances of encountering a dangerous snake are barely 5%.
03:42It is difficult to precisely evaluate the total population of snakes because they tend to remain discreet.
03:49However, scientists can estimate the number of individuals within certain specific species.
03:55Thus, they think that there could be up to a million common striped snakes in the wild.
04:01Charming little reptiles.
04:04Contrary to the widespread striped carnivore, the St. Lucie's snake is one of the rarest snakes in the world.
04:10Its history is full of twists and turns.
04:12First considered extinct, it was rediscovered and then lost again,
04:17before finally being found in 2012.
04:20The survivors of this species are now on the small island of Mariamajor,
04:24after being eradicated from the continent by mongooses and other invasive creatures
04:29that feed on these harmless snakes.
04:32Another factor in the evolutionary success of snakes is their fascinating ability to be fed by the sun
04:38because they depend on external sources of heat or light.
04:42Although they are often called cold-blooded animals, this term is misleading.
04:47The appropriate term is that of ectothermic,
04:49which means that their body temperature is regulated by their environment.
04:53Unlike mammals and birds that maintain a constant temperature,
04:58reptiles must warm up in the sun or find other ways to increase their body temperature.
05:05In addition, some snakes challenge the traditional taxonomy of reptiles by not laying eggs.
05:10Although we are taught at school that all reptiles lay eggs,
05:13nature likes to make exceptions.
05:15About 70% of snakes are actually oviparous,
05:19but those living in colder environments give birth to their young,
05:23because eggs would not survive in such conditions.
05:26Nature always has a way of dispelling our expectations and our nomenclatures.
05:30Snakes form a group of prosperous tetrapods,
05:33although they do not present the four characteristic members of tetrapods.
05:37Despite, or perhaps thanks to this, snakes are extremely diversified.
05:42Although this diversity seems to go back to the era of dinosaurs more than 100 million years ago,
05:48modern snakes seem to have appeared more recently.
05:53Fossils and DNA suggest that snakes would have begun to diversify
05:58and evolve after the massive extinction that ended the dinosaurs.
06:02They would have benefited from the habitat and niches left vacant by the missing species.
06:07In terms of locomotion, snakes are extremely flexible
06:11and can crawl, dig, climb, swim, and some are even able to glide.
06:16The ancestors of snakes were quite different from those we know today.
06:21Some species even had very developed limbs.
06:24They continued to evolve throughout the upper cretaceous,
06:28various species developing all over the world.
06:31Only a few modern snake families appeared later,
06:35millions of years after the extinction of dinosaurs.
06:38The fossil record of snakes is fragmented,
06:41making the reconstruction of their evolutionary history complex.
06:44To clarify this enigma, scientists use DNA analysis.
06:49Molecular clock techniques allow us to estimate when different snake lines merged,
06:55suggesting that most of the diversity of modern snakes would have appeared after the dinosaurs.
07:00Only a few snake lines survived the mass extinction of the late Cretaceous.
07:05But these few survivors gave birth to the incredible diversity of snakes that we know today.
07:11Some families lasted for millions of years before extinguishing,
07:15while others prospered and branched out after the event of extinction.
07:20This pattern of rapid survival and diversification is similar to what we observed in birds and mammals
07:26after the extinction of dinosaurs.
07:29The ability of snakes to dig, hunt in the dark, and survive for a long time without food
07:35helped some species to cross the chaos following the extinction.
07:40Their flexibility and their ability to adapt allowed them to find refuge
07:45and prosper where other species failed.
07:50Snakes may seem frightening to many people,
07:53but most species are harmless and do not interact with humans.
07:58And even if they wanted to, most snakes are too small to pose a real threat.
08:04Some large snakes can nevertheless swallow prey, at least surprisingly.
08:09The biggest animal ever eaten by a snake was a 70 kg hyena,
08:14swallowed by a seba python.
08:17I bet the hyena stopped growling at that moment.
08:20Before that, the biggest meal ever observed was a 60 kg impala
08:24devoured by a python of the same species.
08:27Amazing!
08:28The world's largest snakes are constrictors,
08:31which kill their prey by suffocation.
08:34To consume large prey, the snake must be huge.
08:38Seba pythons, green anacondas, reticulated pythons,
08:42Burmese, Indian, and Amethyst
08:45are all claimed to be the world's largest snakes,
08:48sometimes reaching impressive lengths and weights.
08:52And that's it with snakes.
08:54Burk.