it’s true that there are animals today
notably the blue whale is the largest creature ever to inhabit the earth that
are bigger then dinosaurs but, no creature that
currently walks on land gets anywhere close to the size
the Super Dino’s. The largest recorded species of dinosaur
probably is Amphicoelias Fragillimus, which measured up to 60 meters and weighed 122 metric tons! By comparison, the African savanna
elephant, the largest modern land animal clocks in at just three to four meters
tall and five and a half tonnes – both herbivores! So why aren’t there land mammals today that are as big as the dinosaurs? Well, the fossil record gives us some clues as
to when and how if not exactly why mammals hit their limit. After the last
of the dinos disappeared around 65 million years ago the size and diversity of
mammals went totally nuts… Until it didn’t. Around 30 million years ago, a kind of giant
Rhino-Giraffe beast topped out at five meters tall and seven
and a half meters long grabbing the record for the biggest
mammal to ever walk the earth. Scientists think that there are several
limiting factors that have kept modern land animals from approaching super-saurus
sizes. First mammals give birth to live young, a
mama dinosaur could just lay a bunch of eggs and walk away but a mammal has to gestate and nurse and rear babies at a great energetic cost. Large mammals also have
long periods of gestation. Giraffes and rhinos gestate for about fifteen
months and elephants are pregnant for nearly
two years! And the longer a pregnancy is, the more
dangerous they are for both the mother and the young so on mega-herbivore would
probably experience and unfeasibly long and dangerous pregnancy. Another theory suggests the dinosaurs grew
so large because of Earth’s climate and ecology at the time. A warmer, muggy climate with a higher
carbon content in the air made the vegetation grow off the hook. Sauropods basically lived in a massive smorgasbord, and they
may may have gotten so Titanic simply because they could. But the environment
changed over time and herbivores worse today don’t live in such
prime conditions. Reason number three today’s land mammals are further limited by
their skeletal systems. Sauropod fossils show evidence of avian in like air sacs that made for a much
lighter skeletons than you’d expect in animals so large. Some of these dudes were 30 meters long but
only weighed an estimated forty tonnes. A modern land mammal that size would likely
weigh nearly twice that and basically it be too heavy to get around.
Finally the fourth and maybe coolest reason a mega-mammal would probably cook its own tissues.
Mammals as you probably know are endothermic or warm-blooded. Our bodies
generate and maintain their own temperature internally. Reptiles meanwhile are ectothermic
or cold-blooded absorbing heat from their environment –
like a snake sunning on a rock. There is actually debate as to whether some dinosaurs were
warm-blooded like birds or if they had some sort of an immediate system that
was neither all cold-blooded nor all warm, but regardless we know a mammal
uses way more energy than a similar-sized reptile. So it’s probable that modern land
mammals couldn’t get much bigger than elephants without actually cooking
themselves from within. That’s enough to make me perfectly happy
being this size. Thank you for watching this episode of SciShow, if
you have any questions or comments or suggestions we’re on Facebook or Twitter – and of course down on the comments
below, and if you wanna keep getting smarter with us here at SciShow you can go to
and subscribe.

Author Since: Mar 11, 2019

  1. If are ancestors manage those big game properly and holding back on killing the entire herd or predators then, some of these animal would still exist, Wolly mammoths for example.

  2. What ? That sauropod was 60 m long ? Are we sure about that ? How accurate can this be ? This can't be right I've never heard of any that wee longer than 45 m

  3. 2:25 That's a pretty bad reason. Animals evolve their metabolism along with everything else, and mammals have all different metabolic demands and body temperatures depending on their size.
    If selective pressures would be favorable for large mammals to exist, their metabolisms would adapt accordingly.

  4. Erm elephants whales elk moose polar bears grizzly bears all as big or bigger than most Dino's, get ya bollocks correct.

  5. Another thing about metabolisms is that whatever the metabolism of Dinosaurs was like, they were probably slower than most mammals, meaning they required less nutrition than an equivalent sized mammal.

  6. I think another reason is likely because of the huge number of humans that live in any given area. We do take up a lot of space for a species that is relatively small due to our large numbers.

  7. blue whales are the largest animal ever, the largest living thing is a mushroom

  8. Same reason less mammals fly. Bones aren't hollow, dinosaurs (Like birds) had highly efficient respiratory systems and various other adaptations for being big, the same adaptations that allow birds to fly so well and be pretty much the dominant aerial life forms on the planet. I mean bats are unlikely to outcompete birds in niches that birds fill. They may fill similar niches. But alot of hate are nocturnal, birds don't have echo location though. Good job bats.

  9. Um there are land mammals the size of dinosaurs. We call them every mammal ever. Not all dinosaurs were massive and even Triceratops and Tyrannosaurus Rex were not much bigger than elephants in height. What you mean is none the size of sauropods.

  10. the North American Moose is currently experiencing a species crisis due to tick infestations. food for thought.

  11. I was going to let this go because of how similar they are. But paraceratherium was the largest indricotherium was the runner up

  12. Hey, I've always wondered how could motorcycle balanced while we ride it and how could planes counter angular momentum, especially on planes with odd-numbered engine? Thank you

  13. Its possible that we lack large mammals because early humans killed these kinds of animals off, either out of fear or for our own use (food, clothing, weapons, etc). Ir could be a combination of some or all of these factors, which, I think, is probably what happened.

  14. But what about that giant mammal from 30 million years ago? Your last possible cause sounds more "cool" then plausible.

  15. COZ there are plants that makes them grow to there fullest potential.. these plants are now extinct also… maybe ..? what do u think?

  16. Guys, the giant mammals alive today are ELEPHANTS and GIRAFFES! Stop joking around when people are looking for genuine answers!

  17. I'll go with bone thing, simply because blue whales exist just fine. Weight doesn't matter too much in the ocean.

  18. If giant animals would cook themselves just do what a moose does moose only inhabit cold climates because they can tolerate anything over 80 degrees celcius that’s why they bathe in a lake all the time when it gets hot but giant mammals that evolved in warm climate might not have a way to cool down or find so natural unatural way to do it elephants do it rhinos do it just cool down if you get hot

  19. Large warm blooded mammals have difficulty radiating excess body heat. The larger an animal gets, the larger its volume becomes relative to its surface area. Elephants have large ears to increase their surface area to help radiate more heat.

  20. The Problem of Overheat would a Small mamal have if you make IT giant because of The Heart beating way to fast and its cells producing to much heat. Giant mamals Like The blue wahle dosnt have this Problem because they are breathing Just a few Times per Minute What makes their metabolism less aktive than that of a Mouse. I giant Land mamal would have The Same adaption

  21. Dinosaurs were probably warm blooded. Predators like Raptors and T-Rex were for sure warm blooded. I don't know about Sauropods or other large herbivores but if they share a similar skeletal system as modern birds they might also be warm blooded.

    The Main reason for modern mammals not being able to reach such size is that there's simply not enough vegetation for them to do so. Modern Earth is an ice house planet with land habitat consisting of mostly deserts and other forms of unproductive natural habitats that would make it hard for a large mammals to exist. It also doesnt help that the mammal skeletal system is more dense than the one dinosaurs had.

  22. This makes me wonder why and how exactly elephants have internal testicles despite having issues with heat dissipation, as in mammals that have them outside in a scrotum it's to avoid having them overly warm.

  23. Future is better than now😔
    Amphicoelias was 196 ft remember
    The largest elephant was Palaeoxolodon:40 ft
    Blue Whale:81 ft
    The tallest Deer was Sivatherium yeet just saying

  24. Look up prehistoric flys. From what they have gathered it was the amount of oxygen in the air that made past species grow so big…

  25. Nice. Very inciteful. Not to split hairs though, l don't think dinosaurs were reptiles strictly speaking. Still, damn fine work.

  26. They'd cook from within? Elephants have a body temperature about a degree cooler than that's some flawed ass logic right there

  27. If qctualy a mammal would be 60 meters big it would be basically a dragon and will spit fire to cool itself

  28. Right at the start of the video: "Nothing has ever grown as big as the blue whale, the largest animal ever to inhabit the earth."

    Not even 30 seconds later: "The biggest dinosaur was probably this one, which grew to 60 meters in length."

    Blue whale: 100 feet long.
    60 meters: 196 feet.


  30. That Amphicoelias fragilimus record is really dubious for a number of reasons. We don't have the actual bone that calculation is based on. It was lost to time, and we're working purely on figures made by Edward Drinker Cope on a partial vertebra. We don't even actually know if the original fossil existed. 

    It's also easy to come up with a MUCH smaller estimate than 60 meters using that same vertebra diagram, which other people have done. And we have far more complete fossils of other huge sauropod dinosaurs (Particularly Patagotitan and Argentinasaurus) that, while much smaller than the high end Amphicoelias estimate, are still enormous.

  31. I thought it was all about barometric pressure… A thicker, more chewy atmosphere made for something akin to weighing less..?
    (You're right, I have no degree in biology.)

  32. Mammals need extreme high amount of oxygen in air and pot holes of low oxygen nature destroyed them.

  33. Wouldn't a mammal evolving to grow larger just evolve to produce less heat for itself as well, if it doesn't need it? I mean animals in the cold are known to produce more energy to compensate, why shouldn't evolution be able to dial down our endothermic nature?

  34. I am wondering what are the advantages and disadvantages of laying eggs instead of giving birth to live young

  35. If mammals (and by this you mean land mammals I think) couldn't get much larger than an elephant without 'cooking themselves' through overheating, then how did indricotherium avoid this?

  36. Animals do not live as long as they did before the flood. Also before the flood the air contained 32% oxygen instead of 21% like we have today. The beaver is the only mammal i know today that does not have osification of the bones. Beaver never stop growing until they die or get unhealthy. Before the flood beaver reached 900 lbs in weight!

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