Part of why we’re so fascinated with extinct
dinosaurs, I think, is that some of them were just so big, it’s just hard to imagine animals walking around on the surface of the planet that size Speaking as a mammal that’s about two meters
tall, I gotta say it’s hard to grasp what it would be like, to be in the presence of
a creature as tall as a five-story building. And yet, they existed! From the Jurassic to the Cretaceous Periods,
when our ancestors were the size of voles and shrews, dinosaurs like Supersaurus, Sauroposeidon,
and Argentinosaurus were shaking the Earth. So, how did they get to be so big? And why did we mammals never even come close
to dinosaurs in size? Well, to our credit, the most massive animal
ever is, of course, a mammal: the blue whale. It can get up to 30 meters long and weigh
as much as 145 metric tons — more than twice as heavy as the most massive known dinosaur. But, to be fair, the rules of biomechanics
are different in the water. Buoyancy and blubber can do amazing things,
allowing sea creatures to grow to sizes that would be impossible on land. However, when it comes to the largest terrestrial
animals, mammals were never any competition for the non-avian dinosaurs. There’s always some debate about what the
biggest dinosaur was. But the current record holder for the largest
specimen belongs to the newly-named titanosaur Patagotitan. Experts estimate that this Cretaceous herbivore
stretched over 36 and a half meters, and weighed upward of 64 metric tons. By contrast, the biggest mammal that ever
walked on land was the hornless rhinoceros known as Paraceratherium. It weighed a mere 15 tons, and stood about
5 meters high at the shoulder, roaming Eurasia from Romania to China, at the end of the Oligocene
Epoch, long after the non-avian dinosaurs disappeared. So, how can two such successful and prolific
types of animals end up having such different size constraints? Part of it might have to do with how they
reproduced. Paraceratherium was a placental mammal, like
us, meaning that it gestated its young inside its body. And if this ancient rhino was anything like
the large mammals alive today, that would’ve taken a very long time. Big mammals like giraffes, rhinos, and elephants
usually have only one offspring at a time, and gestation can last longer than some other
kinds of animals live. Elephants, for example, carry their babies
for more than two years! Now consider the dinosaurs. They didn’t really have to carry their babies
at all. Because, all dinosaurs laid eggs. Even the biggest of the giant dinos hatched
from an egg no bigger than a soccer ball. What does this have to do with size? Well, bigger mammal species give birth to
bigger young, which requires a huge amount of time and energy to gestate. Dinosaurs totally bypassed that problem. Instead of having bigger babies, the largest
dinosaurs laid comparatively small eggs, which held equally small hatchlings. Reproducing this way – with babies hatching
and growing outside the mother’s body – removed the size limits that gestation places on mammals. Dinosaurs also had another evolutionary advantage. Their skeletons had a special feature that
mammals lacked: a sophisticated system of air sacs. These sacs were basically pockets of soft
tissue that were connected to the lungs. Think of them as biological balloons. Some of these sacs sat in the body cavity,
next to bones, usually in the neck, back, and hips. But others ran inside the bones themselves. These air sacs helped shape the dinosaur’s
skeleton, and allowed the bones of the biggest dinosaurs to remain light, without sacrificing
strength. How do we know that extinct dinosaurs had
these sacs? Partly, because non-extinct dinosaurs have
them too! Birds have a similar system of sacs that help
draw air into their tiny lungs, while also making their skeletons remarkably light. And if you compare the respiratory system
of birds to those of the giant dinos, you’ll see that the resemblance is pretty striking. In sauropods, for example, the vertebrae of
the neck and back have the same pockets and divots we find in birds today, where these
air sacs were attached. And, when paleontologists scan fossils of
some dinosaur bones, like vertebrae, they often find hollow spaces inside the bones
where the air sacs used to sit. Now, keep in mind that bones with spaces created
by air sacs are different from the hollow bones that you see in the legs of birds and
other theropod dinosaurs. And, not all of the extinct dinosaurs had
these handy air bags. Only the type of dinos known as saurischians
had them. In the traditional dinosaur family tree, this
group encompasses the theropods — that is, the two-legged dinosaurs that include today’s
birds — as well as the sauropods, the quadrupeds that include the giant titanosaurs. All of the rest of the dinosaurs — like the
horned, armored, and duckbilled dinosaurs — are known as ornithischians, and they didn’t
have these features, so they weren’t as light on their feet. And of course, we mammals don’t have anything
like them, either. We retained a skeletal system of dense, heavy
bones that puts a limit on how big we can get before our bones crack under our own weight. But the thing is, these adaptations are just
what allowed dinosaurs to get so big. They don’t tell us why these giants all
got so enormous in the first place! And that’s a totally different evolutionary
question, with lots of possible answers. Maybe living large was a way to stay safe
from predators. Or maybe their size allowed dinosaurs to cover
more ground, or reach higher leafy branches, in search of food. Or maybe there’s something paleontologists
haven’t thought of yet. And then there’s another question to consider:
Was the ability to grow so large really an advantage? After all, the sauropods are gone. So are most of their relatives. Of the entire dinosaur family, only birds
— a single group of saurischian theropods — survives, and they range in size from the
hummingbird to the ostrich. So, today, even if it’s hard for us to picture
a dinosaur as huge as Patagotitan, we can at least understand how animals like it were
physically possible. Perhaps we’re lucky that we never reached
such great heights. Evolutionarily speaking, it seems that bigger
is not always better. So what do you want to know about the story of
life on Earth? Let us know in the comments. And don’t forget to go to
and subscribe! Now do yourself a favor and check out some
of our sister channels from PBS Digital Studios. After all, we all have a lot to learn!

Author Since: Mar 11, 2019

  1. Its really simple to answer from the past years tree's were gigantic and produced alot of oxygen the air was not contaminated witch allow gigantism and if we compared our modern oxygen it is not clean and the results are deformed or mutated animals air is important in the role of growth.

  2. It would be absolutely great to have a time-and-space map of how life on Earth evolved. We see some videos describe animals, other describe fungi or plants, others describe the environment etc etc. But if there was a timelapse of the world map – and where different types of organisms lived on the ever-changing continents, it's would be awesome. Things like average temperature or air composition could be added. I know it's an ambitious request, but it would help so, so much to connect all the information we hear, which, for now, seems more like a myriad of non-connected dots rather than a comprehensive (hi)story.

  3. It is simple; 1st. every family of species will have a giant. Like Giant Bluefin Tuna is 100 times larger than most species of Tuna. 2nd. The terrain and air did not favor the smallest of cousins. Hence the big ones survived. Imagine such huge dinosaurs living in thick rain forest, totally inefficient.

  4. Wait
    If in the dinosaur period
    The largest known species of land creature was almost as big as the blue whale
    And the fact that water is less affected by gravity
    That would mean there was a creature as big or bigger than the blue whale?

  5. I imagine that the habitat played a significant role – if it's physically possible to grow so large, the next step is demand. Was there a demand to grow bigger – I imagine if the habitat during periods was similar to open plains then size would be a major defence against predators as there is fewer places to hide. Coupled with a lower intelligence and likely less social bonds. Our mammals who live in open plains go for size or small enough to burrow and hide. Can you imagine a goat or sheep living on the African plains in the open? What would stop larger predators from having easy meals? So there has to be a size and herd advantage. Then the predators have to either grow as well or shrink to egg scavenge and re-adapt. It's clear they grew in this case.

  6. One thing I never see addressed is the Earth is growing adding tons of material daily. Wouldn't that make a difference over millions of years? Wouldn't the Earth have less gravity in dinosaur times?

  7. I have often wondered if (some) dinosaurs grew large simply because their DNA didn't have the mechanism to stop them from growing. As stated in the video, they all started from an egg no bigger than a soccer ball. The amount of resources required to grow to be 60+ tons would be a lot (obviously more than 60+ tons). Maybe the only limit to their size was how much food they could eat before they ran out of food or before they became food.

  8. I think their huge size is also because back in time there was O4 instead of O2 we have today. Since the oxygen had 4 atoms it also made living beings larger due to necessary larger lungs and bodyshape for that amount of oxygen. But since meteor hit the Earth it had huge impact on Earth's atmosphere so oxygen was reduced to 2 atoms in one molecule. Beings from that event forward started to change it's look and their size started to get smaller and smaller.

    Bugs are the Best proof how they shrunked in the long period of 65M years. Back then smallest spider was a size of a pencil box and smallest fly size of a middle finger

  9. the atmosphere was three times higher than now with more ozone. the earths core was hotter for warmer air. = bigger plants and bigger creatures. fish bowl effect. many disasters have stripped away the atmosphere to where it is today.

  10. I want to know how some dinosaurs took care of the young especially sauropods because they needed years to be so large to have smaller number of predators

  11. way to go douglas howard you are right on. Not only was the atmosphere thicker the O level was at approx at 32%. look at the size of the bugs at that time as to today.

  12. I thought it was something todo with how rich oxygen was back then compared to now oxygen has slowy downgraded over time.

  13. In other words, paleontologist don't really know why dinosaurs is so big and neither does this video answer the question it posed. Maybe they live in water or perhaps earth spun faster then.

  14. But given they lasted so long until their untimely demise – which incidentally had nothing to do with size – dinosaurs existed for at least 100 million years and were large until the end.

  15. They got huge because of more oxygen content in the air plus those overly huge mouths with a itty bitty anus.

  16. Is there any evidence that gravity (weight) was equal to the force experienced today? In addition, could the air pressure have been more dense than it is today? I recognize the for the CE epoch, the percentage of oxygen in the air was greatest in all of time. How is this known?

  17. The reson because those dinosauris has growing so huge was the early earth atmosphere has high oxigen content than today, and the second reason because it was so huge could be the earth gravity could be more low than today ,with a huge gravity the dinos can not grow so giants !

  18. Mammals would've been bigger than dinosaurs were it not for pesky hunters with spears driving one species after another of mammal extinct when it reaches a certain mass of flesh.

  19. Dinosaurs are big because they ate each other. Their evolutionary path was size, whereas humans are technology.

  20. Biggest IS better. The dinosaurs didn't evolve to survive asteroids. And neither can humans. But certainly when the dinosaurs were around, human rats didnt stand a chance.

  21. Hm, I'm sure you weren't implying that, but the ending sort of sounded like you assume that large dinosaurs weren't successful because they're extinct. I mean, the sauropods (just the most stereotypical group of large dinosaurs) existed for roughly 140 million years and it took one of the largest extinction events in earth's history to change that. That's pretty successful in my book.

  22. Dinosaur that big wouldn’t be walking around but would be spending most their time in the water, so much weight that massive on land would be bone crushing because of our gravity.

  23. Was kind of wanting to know WHY. It is not like they had a choice. Same like man, he is what he is and can't change that. So why so big then and never again? What changed.? Why did it change and how did this change come about.?

  24. I wonder what it’s like being born so small that grass towers over you, and then you grow towering over trees.

  25. D- on this one! Almost a complete scientific failure. Most animals alive today have genetic limiters that stop them from growing. If you want an example of this, take a look at Liger, which is a cross between a lion and a tiger. If the female is a lion, the offspring is born with no genetic "brake" on its growth. They just keep growing slowing. One theory behind the large size of a dinosaur is that the air pressure might have been as high as two atmospheres. The other part of this equation is the hypothesis that dinosaurs live to thousands of years of age and without this genetic "brake" just kept growing.

  26. It's how the dots are connected. It's how evolution works. Awesome.
    Dinosaurs rise and rule the world, instead of it we lose a lot of colours, but we gain more ear an brain. Mammals, a better dentitions, more versatile and the chances to survive when a extinction comes. It marked the future.
    It can happens to us.
    You're are awesome. Cheers from Spain (Europe).

  27. I have always wondered if there might have been an environmental condition that allowed such enormous growth…could the Earth's gravity have been weaker at that time?

  28. You forgot to mention that the atmosphere contained more oxygen back then, therefore everything could grow larger

  29. Life naturally becomes larger and more diverse as time goes on.
    Once the Dinosaurs went into huge decline and eventually died out, Mammals became just as large and diverse as them and spread all around the globe.

    sadly though Humans have recently exterminated most of the worlds large animals after spreading to the other continents.

  30. Not just reproduction style but also metabolism. Dinosaurs used their nutrients for growth, mammals used it to generate heat.

  31. Could it be the plant food was less nutritious and a much larger gut system needed to digest it to the maximum possible, the small head was light weight and the long neck would mean the animal did not need to move it's bulk while moving it's mouth to a huge area of food.

  32. I would argue that the Earth then was far warmer and richer and simply more abundant back then. Higher oxygen and CO2 levels. CO2 to grow massive amounts of vegetation and O2 that provides greater energy. Basicallu lots of available food led to larger sizes simply because there were enough calories out there to sustain it.

  33. How much is that in feet and inches? So then I guess if you have a fireplace and want some wood you'll go out and ask for a kilo rather than a chord bcz metrics must be used for all applications. Really, how interesting.
    DYK feet and inches measure has built some of the biggest/best structures and is still used highly successfully by hundreds of millions of people?
    DYK that metric threads on nuts n bolts are weaker than the USCS (US Customary System) of measure? Why not simply use the measure system best fit for the purpose rather than trying to force everyone to use one system for all applications.

  34. How dinosaurs got so big? Obviously food was plentiful, their numbers were few. They probably ate their own dead. They had no growth regulating mechanisms so as long as they found food they'd grow. But (and this is a big one) when food becomes scarce (due to vlimate change or whatever) the biggest ones will die off first and smallest ones being longest lived species

  35. While sauropods may be the largest terrestrial animals and the blue whale to be the largest animal ever, fungi may be the true titans, we always look at just the tip of it but its entire body is hidden underground and can spread out to incredible distances. I'm not kidding look it up.

  36. For a creature that died almost overnight, in geologic terms, they had existed on planet earth for a little less than 200 million years. Homo Sapiens by contrast a mere 200,000 years; Lucy stretches back to about 3 million years. Whether Homo Sapiens can last another 1,000 years is much in doubt.

  37. Animals are big back then because they live in huge super continent, just look at animals that live in large continent theyre biger than any animals who live in small islands.

  38. Hank even managed to look extra nerdy as an extra bonus to this already nerdy subject

    (Yes ! Dino's are nerdy !
    At least during our own most nerdy phase, as about 7 to 10 years youngsters 🙂

  39. Anybody that swallows this crap science that air sacks/spaces in their Bones made them lighter, HAS one Gigantic Air Sack in the Bone called the Human SKULL !! Now that Pseudo Science has solved(?) that riddle, could the Government please send more GRANT MONEY??

  40. I have a question, are there other Influences which made the size of dinosaurs of dinosaurs so large aside from the anatomical? Before watching the video I was thinking of a predatory arms race whereby species could increase in size to gain defence and avoid predation. Also was there significant enough height on the foliage of trees to warrant converging evolution making many dinosaur species become taller?

  41. I've always wondered about how the large dinosaurs circulatory system worked. I know giraffes have a complicated system of check valves in their neck to keep blood from exploding their brain when they bend down to get a drink. I dinosaurs heart is so far above the ground how did it even vet the blood up from its feet?

  42. yeah but when they lived, they lived for millions upon millions of years, much more than the amount of time humans have existed, so it WAS a very successful adaptation

Related Post