# Why are there no dinosaur-size land animals today? **URL:** \ **Category:** Factual Questions\ **Created:** [August 10, 2017, 5:18am UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226 "2017-08-10T05:18:16Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Weisshund](https://avatars.discourse-cdn.com/v4/letter/w/ba8739/32.png) [@Weisshund](https://boards.straightdope.com/u/Weisshund)\ **Post date:** [August 10, 2017, 3:26pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/21 "2017-08-10T15:26:43Z")
Being that big comes as a package deal including the environment and every aspect of it. That environment ceased to exist and i dont think has existed ever since. If the world itself can’t support you being that big, you cant be, mutation or adaptation towards that end would be a failed path. There are a lot of reasons why ultra megafauna worked for 300 million years, the more scientific persons here could give you exact details as we know them, but its a complex combo deal, and it hasnt existed for 65 million years. Even the mammalian ultra mega fauna combo deal ended, leaving us the few hardy yet smaller survivors we have today. One super important thing that you need is, FOOD, the world has to be able to feed your ultra mega fauna. If you are going to be titanic of proportion, the world needs to be overflowing with mass quantities of high density nutrition. That does not exactly describe the current crap selection of grasses and leaves our current feed stock mega fauna survive on. No need for titanic carnivores , if you dont have a vast supply of titanic herbivores, right? ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [August 10, 2017, 3:39pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/22 "2017-08-10T15:39:55Z")
> [@Chronos](#): > > OK, I should have said that elephants have no predators other than humans. But we’ve been on the scene only for a very short amount of time, not long enough for any significant evolutionary changes other than extinction. And more size wouldn’t help against us, anyway. Elephants are big enough to stop any predator that can be stopped by size, so the point remains that there’s no advantage for them to be bigger. Did you miss the part about lions? And African lions are not the largest predators that have existed, or even the largest mammalian predator that has existed (or exists, since some species of tigers are bigger; but then tigers hunt alone). ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [August 10, 2017, 3:53pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/23 "2017-08-10T15:53:47Z")
> [@Darren\_Garrison](#): > > [There is no [del]spoon[/del] consensus.](https://en.wikipedia.org/wiki/Quaternary_extinction_event#Hunting_hypothesis) Actually, I think the prevailing scientific consensus is that humans played a very important role and probably decisive role in most regions. Climate change may have also been important in some limited areas and for some species. But in general, megafaunal extinction is better correlated with the arrival of modern humans than climate change. As noted in the article, mammoths survived on islands much longer than they did elsewhere even though these islands were also subject to climate change. ---
**Author:** ![Weisshund](https://avatars.discourse-cdn.com/v4/letter/w/ba8739/32.png) [@Weisshund](https://boards.straightdope.com/u/Weisshund)\ **Post date:** [August 10, 2017, 4:01pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/24 "2017-08-10T16:01:42Z")
> [@What\_Exit](#): > > I thought the prevailing theory on Mammoth extinction was climate change causing loss of habitat and thus food and not humans? As the ice age ended the Mammoths did not adapt quick enough as forests replaced tundra. Dont think it is quite that simple, i don’t think we exactly know what complex thing was going on. But i also don’t believe the simple"Man killed them all" theory either. If you take north america as an example, we are talking about a low density, low birthrate, high mortality population of hunter gatherers, not the plains buffalo hunters. At best, i figure they simply sped the clock up a tick on an already begun dying event. Many things died that they are not even noted to have been eating and were not predators. And Some large surviving things became smaller. ---
**Author:** ![Hector\_St\_Clare](https://avatars.discourse-cdn.com/v4/letter/h/b5ac83/32.png) [@Hector\_St\_Clare](https://boards.straightdope.com/u/Hector_St_Clare)\ **Post date:** [August 10, 2017, 4:12pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/25 "2017-08-10T16:12:21Z")
> [@abashed](#): > > For one thing there was more oxygen about which promotes growth, although this is just a hypothesis and quite controversial. > > As I said, dinosaurs laid eggs, therefore, reproduction would not have been such a problem, whereas mammals only make one or two young and if they fall prey to disease or lack of food it takes the population a lot longer to recover. Dinosaurs could simply lay more eggs. I daresay, also, that mammalian young require more rearing than dinosaur young did which puts a premium on the parent’s time and energy. Look at elephants and the way their young have a long childhood requiring much parental care. If a calf dies for some reason it will take a long time to replace that individual. > > It’s also possible that sauropods were able to swallow large amounts of food without chewing, increasing body size and permitting the development of bird-like breathing allowing oxygen to be supplied to their bodies more efficiently. > > There is no one reason why today’s animals are not as large as dinosaurs but a complex of reasons. What’s the mechanism for higher oxygen levels promoting growth? I haven’t looked into it but it sounds fairly dubious to me. ---
**Author:** ![Weisshund](https://avatars.discourse-cdn.com/v4/letter/w/ba8739/32.png) [@Weisshund](https://boards.straightdope.com/u/Weisshund)\ **Post date:** [August 10, 2017, 4:21pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/26 "2017-08-10T16:21:36Z")
> [@Colibri](#): > > As noted in the article, mammoths survived on islands much longer than they did elsewhere even though these islands were also subject to climate change. But said mammoths had their own unique adaptation going on which may play a part of their longer survival. Shame no surviving pygmy mammoth to study what adaptations it has made. Santa Rosa didn’t show signs of hunting? Yet they die eventually. ---
**Author:** ![Novelty\_Bobble](https://avatars.discourse-cdn.com/v4/letter/n/a3d4f5/32.png) [@Novelty\_Bobble](https://boards.straightdope.com/u/Novelty_Bobble)\ **Post date:** [August 10, 2017, 5:34pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/27 "2017-08-10T17:34:58Z")
> [@John\_Mace](#): > > Did you miss the part about lions? And African lions are not the largest predators that have existed, or even the largest mammalian predator that has existed (or exists, since some species of tigers are bigger; but then tigers hunt alone). And bears are much, much larger than tigers ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [August 10, 2017, 5:42pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/28 "2017-08-10T17:42:48Z")
> [@Novelty\_Bobble](#): > > And bears are much, much larger than tigers Lions \< Tigers \< Bears. OH MY!! ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [August 10, 2017, 5:57pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/29 "2017-08-10T17:57:54Z")
> [@Novelty\_Bobble](#): > > And bears are much, much larger than tigers The muchness of bearses largerness than tigers is much smaller than the muchness of larger than lions of the largest theropods. ---
**Author:** ![Ignotus](https://avatars.discourse-cdn.com/v4/letter/i/ecc23a/32.png) [@Ignotus](https://boards.straightdope.com/u/Ignotus)\ **Post date:** [August 10, 2017, 6:24pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/30 "2017-08-10T18:24:24Z")
Maybe those huge sauropods simply never evolved any system for growth regulation other than availability of food, and so continued to grow for their entire lifespan? Some of the fossils we find might well be from bicentenarians… Whereas, once some control mechanism had evolved, as it has in mammals, it would probably be an advantage, as it would save resources otherwise wasted on increasing body size for reproductive purposes. ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [August 10, 2017, 6:24pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/31 "2017-08-10T18:24:39Z")
> [@Weisshund](#): > > [snip] … But i also don’t believe the simple"Man killed them all" theory either … [snap] Neither do I … the whole notion of humans hunting down and eating every last horse across the entire continent in a rather short time in preposterous … but this predation _was_ a major stressor … along with climate change … One more major stressor that rarely comes up in these discussions is that humans brought fire with them … and humans knew how to use fire to modify the environment to their benefit … and not necessarily to anything else’s benefit … Each one of these three mechanics alone wouldn’t have driven so many species into extinction … but bring the three (and however more) to bear all at once … we have ecological catastrophe … ---
**Author:** ![TimeWinder](https://avatars.discourse-cdn.com/v4/letter/t/bcef8e/32.png) [@TimeWinder](https://boards.straightdope.com/u/TimeWinder)\ **Post date:** [August 10, 2017, 8:29pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/32 "2017-08-10T20:29:04Z")
> [@watchwolf49](#): > > the whole notion of humans hunting down and eating every last horse across the entire continent in a rather short time in preposterous The Passenger Pigeon would like to disagree. As would the Tasmanian Tiger and a bunch of others. And those only took a few tens of years. We’re talking a timescale of centuries, and many fewer animals to begin with. I’m not saying it’s true, just that it’s not at all preposterous that humans can wipe out a species in a very short time. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [August 10, 2017, 8:37pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/33 "2017-08-10T20:37:29Z")
And the “overhunting” hypothesis assumes\* accidental \*extinction–but what if the people back then decided for some reason that the megafauna were a pest (“Og tired of motherfucking mammoths on motherfucking plains!”) and developed a deliberate policy of extermination? ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [August 10, 2017, 9:15pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/34 "2017-08-10T21:15:13Z")
> [@TimeWinder](#): > > The Passenger Pigeon would like to disagree. As would the Tasmanian Tiger and a bunch of others. And those only took a few tens of years. We’re talking a timescale of centuries, and many fewer animals to begin with. I’m not saying it’s true, just that it’s not at all preposterous that humans can wipe out a species in a very short time. Good point … I should have qualified “neolithic humans” … ---
**Author:** ![Trancephalic](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/trancephalic/32/380_2.png) [@Trancephalic](https://boards.straightdope.com/u/Trancephalic)\ **Post date:** [August 10, 2017, 9:19pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/35 "2017-08-10T21:19:45Z")
Sauropods have hollow bones, which are much lighter per volume than any mammals. This is mitigated by denser mediums like saltwater oceans, so you can get things like the blue whale. Are bats’ wing bones much thinner than those of birds of comparable sizes? Even the larger ones like flying foxes? ---
**Author:** ![Trancephalic](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/trancephalic/32/380_2.png) [@Trancephalic](https://boards.straightdope.com/u/Trancephalic)\ **Post date:** [August 10, 2017, 10:45pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/36 "2017-08-10T22:45:14Z")
Also, the largest ornithiscian (which lack air-sac and hollow bones) was [shantungosaurus](https://en.wikipedia.org/wiki/Shantungosaurus), which is comparable to the largest known land mammals. ---
**Author:** ![igor\_frankensteen](https://avatars.discourse-cdn.com/v4/letter/i/839c29/32.png) [@igor\_frankensteen](https://boards.straightdope.com/u/igor_frankensteen)\ **Post date:** [August 10, 2017, 11:11pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/37 "2017-08-10T23:11:06Z")
Wow. I’m impressed. EVERY SINGLE PERSON MISSED THE OBVIOUS AND ONLY CORRECT ANSWER. ``` Actually, the one that was closest was the joke answer about taxes. ``` Everyone is demonstrating a lack of understanding of evolution and how it ACTUALLY works. I never cease to be amazed that people get it wrong. Here’s the correct answer: Q: Why are there no dinosaur sized land animals today? A: Because there aren’t. That’s it. Nothing has “changed.” Reasoning Hint: You know when ELSE there were no land animals the size of the larger dinosaurs? Answer: Every OTHER of the millions of years they weren’t here. As in BEFORE they were here. Everyone seems to have forgotten that this planet spent millions upon millions of years, with creatures just a few cells in size or less. We didn’t go from zero life, to dinosaurs, to asteroid strike, to humans, and then STOP. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 10, 2017, 11:57pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/38 "2017-08-10T23:57:10Z")
That’d be a valid answer if there were only one species, or one set of closely-related species, of super-large dinosaur. But when you have a wide variety of different diverse species all reaching sizes much larger than the largest land mammals, you start to wonder why. ---
**Author:** ![mmmiiikkkeee](https://avatars.discourse-cdn.com/v4/letter/m/edb3f5/32.png) [@mmmiiikkkeee](https://boards.straightdope.com/u/mmmiiikkkeee)\ **Post date:** [August 11, 2017, 12:41am UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/39 "2017-08-11T00:41:38Z")
> [@aldiboronti](#): > > … Presumably it’s still possible for land animals to get that big… So why no giant beasts today? It’s pretty obvious to me the underlying question is if we know of any reasons that land animals that big _can’t_ exist anymore. ---
**Author:** ![Kron](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kron/32/12444_2.png) [@Kron](https://boards.straightdope.com/u/Kron)\ **Post date:** [August 11, 2017, 1:15am UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/40 "2017-08-11T01:15:06Z")
> [@Darren\_Garrison](#): > > “Og tired of motherfucking mammoths on motherfucking plains!” +1 internet [Previous page](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226.md?page=1) [Next page](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226.md?page=3)