00:00Bam!
00:09The giant asteroid slammed into Earth and a while after that, dinosaurs were gone.
00:14You'd think there's nothing to be afraid of now, but nope, some pretty unique and scary
00:19beasts started to evolve after that.
00:22Back at that time, mammals were going through significant changes.
00:25It seems that some of them, like those similar to horses and rhinos, became giant and powerful
00:31very soon after the dinosaurs were gone.
00:35When dinosaurs were in charge, which was about 145 to 66 million years ago, mammals were
00:41relatively small creatures.
00:43Most of the time, they lived in the shadows of their much bigger enemies to avoid ending
00:47up as their dinner.
00:49Many of them weighed around 22 pounds or even less.
00:54But when the dinosaurs went extinct, mammals finally had a chance to take advantage of
00:58the new environment.
01:00For example, Brontotheris.
01:03It took this opportunity and grew to enormous sizes.
01:06They started at around 40 pounds and eventually reached weights of 4 to 5 tons in just 16
01:13million years.
01:14This sounds long, but it's relatively short in geological terms.
01:18Their large body size gave them and some other mammals an advantage after the dinosaurs disappeared.
01:24Now, they were the dominant and ferocious creatures others were afraid of.
01:29Brontotheris, whose fossils have been found in North America, got this cool name, Thunder
01:34Beasts, from the Sioux people because they believed these fossils came from giant thunder
01:39horses that would roam the plains during thunderstorms.
01:44And it's still a mystery how these Thunder Beasts got to grow so big so quickly.
01:50One of the theories says that they gradually increased in size over time.
01:54Another option is they went through rapid bursts of growth but also had periods where
01:58they didn't quite change.
02:00Or maybe there was a mix of species.
02:02Some were small and some were bigger, but in general, more of them ended up growing
02:07large.
02:08And scientists studied a family tree of 276 Thunder Beasts and realized the third option
02:14fits the best.
02:18It's all competition in nature.
02:20Back in that time, most mammals were small, so there was fierce competition among smaller
02:24plant-eating animals when it came to food.
02:27The larger ones, like Thunder Beasts, faced less competition for the resources they needed
02:32to survive.
02:33So bigger species had more chances to stay, while the smaller ones went extinct quickly.
02:41So yeah, the end of the dinosaur era doesn't mean the end of impressive and giant animals
02:46you'd also run away from.
02:48For example, I definitely wouldn't like to face this fella.
02:52It kind of reminds me of a giant sloth at first, but those evolved tens of millions
02:57of years later.
02:59This giant lived somewhere between 50 and 60 million years ago in North America.
03:04It was around 8 feet long and had an unusually massive and thick body and legs.
03:10Its tail was very thick as well.
03:12This beast must have used it to support itself and stand on its hind legs.
03:17Its skull was relatively short and small compared to its large body.
03:21What's interesting is that it still had collar bones, which are bones that most hooved
03:26animals don't have anymore.
03:29Here's something comforting that makes it less scary though.
03:31They probably ate plants that were soft enough to chew easily.
03:38Now imagine a snake so big it could easily rival the size of a T-Rex.
03:43It's not some mythical creature from fiction movies, but Titanoboa, the incredible beast
03:49that lived around 60 million years ago in the lush forests and rivers of South America.
03:55It was the largest snake ever that we know about.
03:57It was actually like the ancient ancestor of today's boas and anacondas that still
04:02live in the same region.
04:04Its body was a mind-boggling 42.7 feet long, which is longer than a school bus!
04:11To support its giant body, Titanoboa had about 250 vertebrae, which are the bones that make
04:17up the backbone of animals.
04:20Imagine how much it needed to eat to maintain such a massive body that was as heavy as a
04:25small car!
04:26It went after fish and crocodiles that lived in the waters and rivers of its home.
04:31A snake taking down a crocodile?
04:33It had to be a powerful beast.
04:36Titanoboa holds the record at the moment, but scientists believe we might discover more
04:41fossils of snakes that could be even bigger than this one!
04:47You know there has to be some scary crocodile on the list.
04:51Back in the dino era, there were even crocodiles that were 40 feet long and enjoyed snacking
04:55on dinosaurs.
04:57You can tell they haven't become less scary even after that!
05:01This beast lived between 15 million and 55 million years ago in what is now Venezuela,
05:06Peru and Argentina.
05:08It belonged to a group that was there during the time of the dinosaurs, but like many others,
05:13got to live their best years and thrived after the dinos disappeared.
05:18Unlike most crocodiles that stick to the edge of the water, you could easily come across
05:23this one since it liked to take walks on the land to check what was happening around.
05:28Check out its flattened blade-like teeth.
05:30They remind of those carnivorous dinosaurs even more than other crocodiles!
05:35This adaptation helped with catching prey during its chill afternoon walks on land.
05:40This fearsome creature could grow to over 20 feet long and weigh more than 3,000 pounds,
05:46which is bigger than today's saltwater crocodiles!
05:53Even a rhinoceros came in the XXL size in those post-dino times!
05:58This one, whose name I can't even try to pronounce, was a massive herbivore that lived
06:03in eastern Eurasia.
06:05It looked like a rhino, but it still had some differences, like its neck that was stretching
06:10over 6 feet long, which made it look like a rhino with a giraffe's neck.
06:15The creature stood more than 15 feet tall at the shoulder, towering over most other
06:20animals of its time.
06:22It looked slender, but it's still incredibly heavy with its 33,000 pounds, which is like
06:28two to three grown African elephants, or even a small house!
06:35One of the biggest carnivores that wandered Ice Age Australia wasn't a mammal, but this
06:40frightening reptile called Megalania.
06:43It could grow to be over 18 feet long, which is more than twice longer than the Komodo
06:47dragon, one of the largest lizards alive today!
06:51Megalania had sharp curved teeth similar to those of Komodo dragons, which means its bite
06:57was extremely powerful, and maybe even venomous.
07:01This venom worked in a way it could have prevented its prey from healing property, which means
07:06the poor animal would become weaker, so Megalania didn't even have to work that much to catch
07:10it after that first bite, no matter where its prey would try to escape!
07:17Moving on to birds now!
07:20An elephant bird stood almost 10 feet tall and weighed over a thousand pounds!
07:25You could see it on the island of Madagascar more than a thousand years ago, which is
07:30not even that long ago compared to the others!
07:33One of the multiple species of elephant bird was so big that it could rival some non-avian
07:38dinosaurs such as Euteraptor when it came to size!
07:42And its eggs were gigantic too!
07:45Just one egg could weigh more than 20 pounds, which is heavier than a bowling ball!
07:50The interior of its egg had a lot of space, so much you could hold more than a hundred
07:55chicken eggs inside!
07:59Land and air weren't safe from big beasts where you couldn't be sure if it wanted to
08:03eat you or your salad.
08:05And it was not much different in the water either.
08:08You've heard of Livyatan, right?
08:10It was an ancient, powerful predator and a type of sperm whale, but much larger and more
08:16fearsome than those we know today.
08:18While modern sperm whales mostly eat squid, Livyatan probably had a little bit different
08:24diet, which included other whales.
08:28Another giant predator was also roaming around the same time and place as Livyatan.
08:34Who else but our dear Megalodon shark!
08:37Scientists believed Megalodon also went after other whales, and the fight for the sweetest
08:42bite or even among each other was probably spectacular!
08:47That's it for today!
08:48So hey, if you pacified your curiosity, then give the video a like and share it with your
08:53friends.
08:54Or if you want more, just click on these videos and stay on the Bright Side!
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