# 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:** 4
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [August 11, 2017, 5:37pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/61 "2017-08-11T17:37:08Z")
> [@Malthus](#): > > I’m on the border with that argument as well. > > We have to also account, as I pointed out upthread, for why the largest animal ever to exist, exists today (the Blue Whale). > > If sea animals are likewise likely to have some (not all) who get as big as possible because size = a certain set of advantages, what limits existed in the past on their growth that don’t exist now? > > To my mind, it is possible that there is a certain amount of randomness at work. It’s possible whales couldn’t grow to the size of Blues without enough food, and that you don’t get enough krill to sustain that size without a Southern Ocean as it exists today, with the Circumpolar Current. Which has only existed for the last 20-30 Ma or so. Which matches with the evolution of Baleen whales 26-17 Ma ago. ---
**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 11, 2017, 6:22pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/62 "2017-08-11T18:22:19Z")
> [@MrDibble](#): > > That’s not the argument - the argument is that some animals (not all of them) are _always_ going to get as big as they can possibly get, because that confers one set of advantages. It just happens that in the past, that maximum size was larger than possible today, because of the oxygen levels. That’s not environmental determinism, that’s an environmental limitation. > > I don’t particularly buy that argument, [because the jury’s still out on Cretaceous oxygen levels](https://www.sciencedaily.com/releases/2013/11/131118081043.htm), but it’s not the same argument you’re arguing against. I understand that thinking, but I’m very skeptical. I claim no biological or medical expertise, it’s just that for every limitation I’ve heard suggested about any environment, there have been other factors or elements which can make whatever possible anyway. The main thing I’m trying to get at for the purposes of this exact thread concern, is that there is no NEED for any special explanation for why we don’t have giant creatures. That’s why I pointed out that there were other times in the eons past where there were no giants. We might right now, be on an evolutionary path which leads us BACK to a land of giants again. Elephants aren’t in danger because of a shortage of oxygen. Despite great advances in DNA analysis, we still can’t say exactly what causes a given creature to stop growing at one specific size. More than anything else, there is absolutely no scientific support for any claim that the size of a given creature is the result of a DECISION. Any given creature which appears to be “successful” in it’s environmental niche,\* might\* be better off if they were larger. There’s no way to know, because they are the size they are. Part of my consternation and argumentitiveness about this, comes from my background in History and Archaeology. The bane of our discipline, are people who postulate and then build on “explanations” for events or artifacts they come across, based on the assumption that things HAD to be that way. This has often caused investigations of the past to go off on the wrong track for ages, before someone takes a fresh look at things, and realizes that the initial guesses were wrong, and then everything else has to be rewritten. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [August 11, 2017, 7:04pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/63 "2017-08-11T19:04:11Z")
> [@igor\_frankensteen](#): > > I understand that thinking, but I’m very skeptical. I claim no biological or medical expertise, it’s just that for every limitation I’ve heard suggested about any environment, there have been other factors or elements which can make whatever possible anyway. No, that’s decidedly not the case. For instance, you _can’t_ get land arthropods as big as \*Arthropleura \*today. You just can’t. In that case, it’s definitely the environmental limitation. There is no real debate about it at all. > [@](#): > > The main thing I’m trying to get at for the purposes of this exact thread concern, is that there is no NEED for any special explanation for why we don’t have giant creatures. I wouldn’t say “need”, but that doesn’t make explanations _wrong_. > [@](#): > > That’s why I pointed out that there were other times in the eons past where there were no giants. Well, sure, the Burgess fauna were all pretty small… > [@](#): > > We might right now, be on an evolutionary path which leads us BACK to a land of giants again. Naah. Big land animals are not going to evolve again. Not unless humans die out. We would not tolerate the competition for resources. > [@](#): > > Elephants aren’t in danger because of a shortage of oxygen. No-one’s suggested anything like that argument. > [@](#): > > Despite great advances in DNA analysis, we still can’t say exactly what causes a given creature to stop growing at one specific size. That’s not the point - what the built-in cutoff is for creatures, if there is any, runs headlong into what their physiology will allow, at some point. And for land mammals, it looks like it’s about the same order of magnitude as an elephant. Consistently. > [@](#): > > More than anything else, there is absolutely no scientific support for any claim that the size of a given creature is the result of a DECISION. Who has said it was? > [@](#): > > Any given creature which appears to be “successful” in it’s environmental niche,\* might\* be better off if they were larger. There’s no way to know, because they are the size they are. Sorry, no. When there are clear trends in increasing size, and then the trend stops, it’s perfectly reasonable to ask “why?” > [@](#): > > Part of my consternation and argumentitiveness about this, comes from my background in History and Archaeology. The bane of our discipline, are people who postulate and then build on “explanations” for events or artifacts they come across, based on the assumption that things HAD to be that way. This has often caused investigations of the past to go off on the wrong track for ages, before someone takes a fresh look at things, and realizes that the initial guesses were wrong, and then everything else has to be rewritten. That’s Science - hypothesis, research, disproof…the problem there isn’t the people coming up with the explanations, it’s the people who are slow to disprove them. ---
**Author:** ![Malthus](https://avatars.discourse-cdn.com/v4/letter/m/85f322/32.png) [@Malthus](https://boards.straightdope.com/u/Malthus)\ **Post date:** [August 11, 2017, 8:08pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/64 "2017-08-11T20:08:14Z")
> [@MrDibble](#): > > It’s possible whales couldn’t grow to the size of Blues without enough food, and that you don’t get enough krill to sustain that size without a Southern Ocean as it exists today, with the Circumpolar Current. Which has only existed for the last 20-30 Ma or so. Which matches with the evolution of Baleen whales 26-17 Ma ago. That’s certainly possible. The question is whether the Southern Ocean, as it exists today, with its intensive concentration of krill, is a historically unique occurrence, such that similar conditions did not exist in past continental/oceanic configurations. If the theory is that, all things being equal, some creatures tend to grow to the largest size not prohibited by hard limitations, that in effect there’s a “big creature niche” that will be filled unless something prevents it, then the lack of Blue Whale sized prehistoric creatures could tell us something about past environments … Alternatively, it could be that certain species simply through random chance (or rather an accumulation of random mutations) blunder into an evolutionary advantage as a result of size - one that _could_ have been utilized by other creatures at another time, but simply _wasn’t_. I really wonder what the current scientific thinking is on this. Certainly there is plenty of convergent evolution that would tend to argue that certain forms will simply be replicated over and over again, because they work. Presumably that goes for gigantic creatures as well. ---
**Author:** ![Lemur866](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lemur866/32/434_2.png) [@Lemur866](https://boards.straightdope.com/u/Lemur866)\ **Post date:** [August 11, 2017, 8:38pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/65 "2017-08-11T20:38:17Z")
It’s not all just random. It’s heritable randomness combined with selection. Creatures get bigger or smaller. If the ones that are bigger have more offspring than the ones that aren’t, and the size difference is heritable, the species gets bigger. If the ones that are smaller have more offspring than the ones that aren’t, and the size difference is heritable, the species gets smaller. It turns out that there are lots of heritable ways for a creature to be larger or smaller. And there are lots of environments out there, some in which a larger creature would be more successful, some in which a smaller species would be more successful, and some in which staying the same size would be more successful. An Elephant doesn’t have to be a large animal because there’s some genetic law that they must be the size of an elephant. There have been lots of dwarf proboscidean species. It’s just that most times larger sizes work out better for elephants, and so large sized elephant species evolved and persisted. But sometimes those large elephants found themselves in an environment where smaller size was advantageous–like an island with no large predators–and so a new species of dwarf elephant evolved. The point is that what seems to be stasis is actually selection. If a species stays the same size it’s because smaller or larger individuals aren’t as successful as the medium sized ones. But of course that random heritable variation has to be present. This is why elephant species can be larger, or smaller, but you never see an elephant species that can fly. Would it be advantageous for elephants to fly? Yes, no, maybe? But unless this heritable variation appears it doesn’t matter how much of an advantage flying would or would not be to an elephant. One more nitpick. Mammals have been around for much longer than 65 million years. True Mammals have been around since the early Jurassic. Therapsids have been around since the early Permian. Synapsids go back to the Carboniferous. And what you want to call a “mammal” is just a matter of names, it traditionally just means an Amniote with a single jaw bone instead of four, because that’s a trait that can be easily observed in the fossil record, while things like hair or mammary glands aren’t. ---
**Author:** ![CarnalK](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnalk/32/486_2.png) [@CarnalK](https://boards.straightdope.com/u/CarnalK)\ **Post date:** [August 11, 2017, 9:22pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/66 "2017-08-11T21:22:19Z")
> [@abashed](#): > > 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 assume you mean large mammals because a whole bunch of mammals produce litters of more than two. Like dogs, cats, rats, mice, pigs, raccoons, etc. If that’s what you meant, do we have a reason to think large dinosaurs laid a lot of eggs at a time? I also kind of fail to see your point about how egg laying=easy reproduction. You can’t “simply lay more eggs” for most creatures. Some few store sperm and make multiple batches of fertilized eggs, but many have to mate again. Many animals still need to build and guard a new nest. ---
**Author:** ![Lemur866](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lemur866/32/434_2.png) [@Lemur866](https://boards.straightdope.com/u/Lemur866)\ **Post date:** [August 11, 2017, 9:29pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/67 "2017-08-11T21:29:04Z")
> [@CarnalK](#): > > I assume you mean large mammals because a whole bunch of mammals produce litters of more than two. Like dogs, cats, rats, mice, pigs, raccoons, etc. If that’s what you meant, do we have a reason to think large dinosaurs laid a lot of eggs at a time? Also lots of mammals back in the Jurassic laid eggs. There’s a strong tendency for people to imagine that human beings are a typical mammal, and so we get the incorrect assertion that mammals typically have one or two babies at a time, or that mammals have really big brains, or that evolution was some sort of system whose intention was to produce human beings. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [August 12, 2017, 12:31am UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/68 "2017-08-12T00:31:51Z")
The simple answer may be that larger mammals have had no major competitive advantage over ones less large that is not more than offset by the disadvantages The likely contributors to that have been laid out: Changing climate, in particular fairly rapid warming after the last glaciation and much drier as well, harder for a larger mammal to adapt to than a smaller one. Rapidly changing environment independent of climate cause by human interactions with the environment, such as by human started fires. Human predation. One major advantage of gigantism through evolutionary history has been that it protected them from predation; humans acting as an intelligent social group with culture and tools/techniques passed on between generation reduced or eliminated that advantage. But a theme through there is the need to have adapted to _fairly rapidly changing_ times, both caused by natural climate change and human induced changes both via the environment and as a new predator that changed approaches very quickly. Large mammals have fewer individuals per unit area, fewer young per generation, require more adult inputs to survive, and have longer periods of time between generations, than do small mammals. That’s just less chance to find a genetic variant that works as the world rapidly shifted. It is perhaps more useful to ask why sauropods (and only sauropods) _were able_ to produce so many examples of gigantism because pretty much they are the only group that have to that degree. As cited earlier in this thread several mammals have gotten up to 15 tons and maybe one over 20 tons but sauropods are the _only_ group of land animals that commonly exceeded 20 tons, some possibly over 100 tons. So rather than ask what stops mammals from doing so it may be more useful to explore what drove and allowed sauropods in particular _to_ do so relatively so commonly over their time on earth. They were the special case of all land animals including other dinosaur groups. Why not any others? ---
**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 12, 2017, 1:12am UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/69 "2017-08-12T01:12:21Z")
> [@md2000](#): > > Yes and no. > > Evolution is random chance combined with selection for better fitness. > > For example, the common wisdom is that we descended from trees to scavenge the plains. No, that’s not the common wisdom. The common wisdom, such as it is, was that the tress got scarcer and we had to either make a living on the plains, move where the forests were still thick, or die (or, of course, maybe something else). Some of our relatives probably “chose” different paths and we’re here because we happen to be the ones that descended from the group that stayed put and learned to liven on the plains. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [August 12, 2017, 1:17am UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/70 "2017-08-12T01:17:56Z")
Sort of agree with **igor** ’s objections and sorta not. He’s 100% correct to attack the idea of evolution having a goal. Which some folks’ lazy phraseology can be read to imply. But he throws out a chunk of baby along with the useless bathwater. As **Lemur866** said, successive generations get bigger if A) there is heritable variation and B) bigness confers relative advantage in that environment at that time. So in that sort of environment for those particular species increasing size over time is 100% definitely _caused_. What it is not, \*pace \ ***igor** , is a goal or a design point. We can look on various factors in an environment through something akin to the anthropic principle. Pre-technological humans can’t live on a planet with widespread 150F surface temps or a 1% oxygen atmosphere. So it’s not surprising we don’t find those temps & oxygen levels here. Why not? Because we’re here to see the local temps and oxygen levels. There’s a “blue-whale-thropic” principle that says the current oceanic environment _must_ be consistent with blue whales. Why? Because we see blue whales. The causation does \*not \*however run the other way: the existence of ocean conditions such as we see (temp, salinity, oxygen, food types & quantities, etc.) does not guarantee that blue whales exist or even that they could evolve from some other similar species. It definitely does not imply that blue whales \*must \*exist. The collective set of “species-thropic” principles define the playing field upon which the possible species contend for headcount with other species and for variations within those species. Including variations leading to further speciation. There is a very large size difference between the largest sauropods and the largest extant land critters. As a matter of mere logical formalism, it’s correct to say that differences in species-thropic limitations between then vs. now cannot be \*proven \*to be the cause of the size difference we see. But it’s sure the way to bet. All the more so because the evidence is not for one ancient giant species, but for a great many species with near-global distribution. Giant species went from numerous and widespread to 100% absent. The giant-thropic principle says conditions were right then. The sheer effectiveness of life at exploiting most niches strongly implies the same degree of giant-thropic conditions does not exist today. ---
**Author:** ![Sailboat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sailboat/32/461_2.png) [@Sailboat](https://boards.straightdope.com/u/Sailboat)\ **Post date:** [August 12, 2017, 1:47am UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/71 "2017-08-12T01:47:14Z")
> [@CarnalK](#): > > do we have a reason to think large dinosaurs laid a lot of eggs at a time? My understanding of current theory is that sauropods (the largest dinosaurs) are believed to have laid a large number of eggs but scattered in separate nests, not all together, to mitigate the effects of nest predation (_literally_ not putting all their eggs in one basket). Some have suggested that, since young sauropods were essentially defenseless, whereas adults were extremely difficult prey, they used a “strategy” of laying many eggs so that predators could not eat all the young before a few reached giant size. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [August 12, 2017, 2:41am UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/72 "2017-08-12T02:41:52Z")
> [@LSLGuy](#): > > … the evidence is not for one ancient giant species, but for a great many species with near-global distribution. … Again, yes multiple species, but only one single suborder. None of similar size among the ornithischian dinosaurs, none among the theropods, even the close sister group prosauropods did not get over that 20 ton mark. [An article which discusses on the uniqueness of sauropod gigantism.](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3045712/) So far I’ve only read the abstract which references the advantage of the long neck allowed by a small brain and pneumatization of the axial skeleton among other drivers. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [August 12, 2017, 3:42am UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/73 "2017-08-12T03:42:39Z")
From that article as I read … > [@](#): > > … Large body size evolved very early on and remained a hallmark throughout sauropod evolution (Dodson, 1990). The discrepancy in body size between other dinosaurs and sauropods, as well as between the largest land mammals and sauropods (Figs 1, ​,2),2), has recently been highlighted … The largest representatives of all other dinosaur lineages, despite being very big in general perception, rarely exceeded the 10 t threshold and thus actually are in the size range of very large terrestrial mammals such as the fossil indricotheres (Fortelius & Kappelman, 1993) and extant and fossil elephants … > > … the long necks of sauropods allowed them to feed not only at heights out of reached of other herbivores, but also over a large volume without moving the massive body. … > > …Very large sauropod humeri (Buffetaut et al., 2002) from the Triassic of Thailand document the very rapid evolution (within a few million years after their origin) of very large body size in sauropods (Buffetaut et al., 2002; Sander et al., 2004). This rapid body size increase resulted from an evolutionary increase in growth rate compared to relatively small basal sauropodomorphs such as Plateosaurus (Sander et al., 2004). This increase in growth rate appears to be linked to the evolution of tachymetabolic endothermy in the sauropdomorph lineage (Sander et al., 2004; Sander & Klein, 2005; Sander et al., in press b; see also section II.10b). … > > … All else being equal, would an increased level of atmospheric oxygen allow the evolution of gigantic terrestrial tetrapods? … the hypothesis of Hengst et al. (1996) is superseded by the likely presence of a bird-like lung in sauropods and the current understanding that oxygen levels were significantly lower in the Jurassic and Cretaceous than today (Gans et al., 1999; Dudley, 1998; Berner, 2006; Berner et al., 2007; see also Fig. 8) or at about the same level … > > … Another hypothesis that has been advanced is that an up to tenfold higher CO2 content of the Mesozoic atmosphere than today (e.g. Royer et al., 2004; Berner, 2006; see also Fig. 8) increased plant productivity, thus allowing larger body size on the same plant resources (Paladino et al., 1997; Burness et al., 2001; Maurer, 2002). However, experiments have shown that while an increased CO2 level does increase plant productivity, the decrease in protein content and increase in levels of nonstructural carbohydrates and phenolics in sum result in a decreased food quality … we suggest that increased atmospheric CO2 levels were not a prerequiste to the evolution of gigantism in sauropods. … > > … Higher average ambient temperatures are also worth considering because they would tend to blur the concepts of endo- versus ectothermy: with high ambient temperatures, homoiothermy can be achieved in large, compact animals with a low metabolic rate (Spotila et al., 1991), whereas tachymetabolic species face overheating in the absence of effective physiological or behavioural cooling mechanisms. Thus, large size could provide the advantages of a high, constant body temperature at low cellular metabolic cost … > > … Another extrinsic biotic hypothesis is that sauropod gigantism was made possible by some or all of the plant groups of the pre-angiosperm flora, such as cycads, ginkgoes, conifers, and ferns, being more nutritious than the plant groups preferentially ingested by modern herbivores, namely grasses and dicot leaf browse … While some Mesozoic plants were both highly nutritious and abundant, there is no evidence from fermentation experiments to explain sauropod gigantism through more nutritious food. In addition, even if Mesozoic forage was more nutritious than modern forage and would have made gigantism possible, one would have to explain why this led to the unique gigantism of sauropod … > > … We now want to explore evolutionary innovations that may have made more resources available to the individual, leading to gigantism in sauropods (Figs 6, ​,8).8). The most important of these is the hallmark of sauropod anatomy, the long neck. Potential selective advantages conferred by the long neck can be framed as two hypotheses. The first hypothesis is that the long neck allowed adult sauropods to exploit food resources beyond the reach of other large herbivores or smaller individuals of the same sauropod species, e.g. plant matter high above the ground. The second hypothesis is that a long neck and the resultant large feeding envelope would have conveyed a considerable energy savings in feeding as opposed to moving the whole body while feeding. … > > … We posit that the long neck of sauropods was central to the energy-efficient food uptake of sauropods because it permitted food uptake over a large volume with a stationary body. > In the Late Triassic and Early Jurassic (210–175 million years ago), the combination of biological properties listed above led to an evolutionary cascade in the sauropodomorph lineage characterized by selection for ever larger body size, mainly driven by predation pressure from theropod dinosaurs. … FWIW. _No other_ land animal has, apparently had a similar combination of environment and specific features possible within their biology. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [August 12, 2017, 4:32am UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/74 "2017-08-12T04:32:07Z")
> [@](#): > > … Another extrinsic biotic hypothesis is that sauropod gigantism was made possible by some or all of the plant groups of the pre-angiosperm flora, such as cycads, ginkgoes, conifers, and ferns, being more nutritious than the plant groups preferentially ingested by modern herbivores, namely grasses and dicot leaf browse … While some Mesozoic plants were both highly nutritious and abundant, there is no evidence from fermentation experiments to explain sauropod gigantism through more nutritious food. In addition, even if Mesozoic forage was more nutritious than modern forage and would have made gigantism possible, one would have to explain why this led to the unique gigantism of sauropod … One item briefly mentioned on was grass. IIRC the reason for so many great dino fossils was that they were constantly being buried in mudslides and heavy sediment movement. Grass root matte has reduced much of that erosion. Plus grass grows thinner and shorter than the listed growth in the quote - so there is substantially less food source - good or bad - in grasslands. As has been mentioned, grazers eating grass full time seem to have an upper limit in size, based on how much nutrition they can consume. My impression from articles and illustrations is that the plant environment of the dinosaur era was a lot of large ferns, palms, and other giant-leaf plants presenting a much greater volume of food for any animal that could reach it. The bigger examples today - such as elephants and giraffes - seem to exist in a borderland between forest and grassland where there are plenty of trees big enough to feed off, but spaced widely enough to not impede the passage of oversized beasts. The biggest grazer I can think of in North America might be the moose or bison; the former is semi-aquatic and tends to live in swamps and an area with small trees it can often push its way through. The latter basically seems to have been instrumental in preventing much tree growth in its prairie range. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [August 12, 2017, 12:04pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/75 "2017-08-12T12:04:15Z")
> [@DSeid](#): > > From that article as I read … > > FWIW. _No other_ land animal has, apparently had a similar combination of environment and specific features possible within their biology. The theory that the long neck was all about minimizing moving the body makes me think of modern dragline or bucket-wheel mining machines with their ponderous body and relatively nimble and outstretched scoop. The connection to Fred Flintstone’s job at the quarry operating a bronto-crane is satisfying somehow. Overall an excellent cite. Clearly something was different about the environment. Or more accurately, several somethings. Which ones mattered and helped feed the positive feedback loop on size and which ones were merely coincidental is still a big Q. Side item: As you’ve cited, that one suborder of sauropods were the only truly huge dinos. At the same time there were (it seems) a greater preponderance of biggish beasts then versus now. IOW dozens of unrelated species of roughly elephant sized critters. The same mid-scale giantism seems to have infested the early seas such as [Plesiosaur - Wikipedia](https://en.wikipedia.org/wiki/Plesiosauria) Evolution is not goal directed. But in the presence of competition, critters become more highly fitted over time to their environment whatever it is. In the presence of a long term more or less static environment, the critters get “better”, and a species from e.g. 100K years earlier wouldn’t compete successfully against species from e.g. 100K years later even if the rest of the physical and plant environment was unchanged. I wonder how much we can think of bigness as a crude “v1.0” approach to surviving predation pressure or augmenting food availability? Later methods such as herding, speed, keen sight or smell, more specialized feeding techniques, more intensive nest guarding or young nurturing, etc., might be more sophisticated “v2.x” innovations that achieve the same survival advantage at less raw metabolic cost? It takes time, and lots of it, for these design innovations to first occur then mature. Perhaps, like DOS, giantism is simply a now-obsolete solution to inter-species fitness. ---
**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 12, 2017, 1:02pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/76 "2017-08-12T13:02:09Z")
The theropods might never have reached the size of the largest sauropods, but they did get significantly larger than the largest current land animals, somewhat larger than the largest land mammals ever, and significantly larger than any non-theropod land carnivore ever. On blue whales, remember that the blue whale is the largest animal ever _that we know of_. Maybe the remains of the precursors to their niche are all buried under the ocean floor (that is, the part that’s still ocean floor), and so we’ve never stumbled upon them. Maybe those precursors were invertebrates, and so left very little in the way of remains at all. We can’t be completely certain that there was never anything else of blue whale size, or larger. ---
**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 12, 2017, 1:02pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/77 "2017-08-12T13:02:16Z")
> [@md2000](#): > > Plus grass grows thinner and shorter than the listed growth in the quote - so there is substantially less food source - good or bad - in grasslands. Grass grows thin and short in grasslands where that there is some limiting factor that doesn’t allow anything bigger to grow. Grass can develop [tall species](http://homeguides.sfgate.com/fastest-tallest-growing-ornamental-grasses-45363.html) in areas that can support it. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [August 12, 2017, 3:12pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/78 "2017-08-12T15:12:11Z")
> [@md2000](#): > > The bigger examples today - such as elephants and giraffes - seem to exist in a borderland between forest and grassland where there are plenty of trees big enough to feed off, but spaced widely enough to not impede the passage of oversized beasts. They don’t just “seem to exist” in that ecotone- they (at least, the elephants) actively [make it so](https://www.youtube.com/watch?v=XlGGjIKxBvk). ---
**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 12, 2017, 3:16pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/79 "2017-08-12T15:16:50Z")
Unless you happen to be a [forest elephant,](https://en.wikipedia.org/wiki/African_forest_elephant) which is now considered to be a distinct species. ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [August 12, 2017, 3:49pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/80 "2017-08-12T15:49:51Z")
> [@LSLGuy](#): > > the evidence is not for one ancient giant species, but for a great many species with near-global distribution. Giant species went from numerous and widespread to 100% absent. The giant-thropic principle says conditions were right then. The sheer effectiveness of life at exploiting most niches strongly implies the same degree of giant-thropic conditions does not exist today. > [@DSeid](#): > > Large mammals have fewer individuals per unit area That reminds me of another hypothesis: that the continental masses as they were configured in the Mesozoic formed a single enormous ecosystem large enough to support a stable population of animals with larger body masses than today. However I don’t know how well that holds up; hadn’t the proto-Atlantic already begun forming by the Cretaceous? [Previous page](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226.md?page=3) [Next page](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226.md?page=5)