# why did the dinosaurs not evolve back **URL:** \ **Category:** Factual Questions\ **Created:** [August 13, 2013, 3:34pm UTC](https://boards.straightdope.com/t/why-did-the-dinosaurs-not-evolve-back/666138 "2013-08-13T15:34:17Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Little\_Nemo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/little_nemo/32/3120_2.png) [@Little\_Nemo](https://boards.straightdope.com/u/Little_Nemo)\ **Post date:** [August 13, 2013, 5:03pm UTC](https://boards.straightdope.com/t/why-did-the-dinosaurs-not-evolve-back/666138/21 "2013-08-13T17:03:46Z")
Evolution is not about arriving at some destination. Animals don’t evolve until they become humans or tyrannosauri and then declare they’ve won the game. Evolution is an ongoing process of change. Animals change in random ways. If the changes are bad, the animals die and the changes disappear. If the changes are good, the animals live and breed and the changes spread through the species. ---
**Author:** ![breakneck](https://avatars.discourse-cdn.com/v4/letter/b/e99b99/32.png) [@breakneck](https://boards.straightdope.com/u/breakneck)\ **Post date:** [August 13, 2013, 5:24pm UTC](https://boards.straightdope.com/t/why-did-the-dinosaurs-not-evolve-back/666138/22 "2013-08-13T17:24:14Z")
> [@Great\_Antibob](#): > > What do you mean by “evolve back”? The descendants of (some of) the dinosaurs are still around and kicking. > > You may as well ask why human beings don’t go back to being unicellular life forms. > > Most weren’t. Most mammals aren’t elephant sized, either. > > Look at mammal fossils from 10 million years ago. We tend to put the larger specimens in museums and those are the ones we remember. It doesn’t mean 10 MYa animals were all large. > > No, and why would they have to be? Do cows eat larger plants than sheep? Do cows eat larger plants than squirrels? Or do they just eat more than their smaller counterparts? > > Also, some dinosaurs (just like some modern animals) didn’t feed on plants. > > Ask the same question for meat-eaters. Do large meat-eating animals always eat larger prey? > > The largest single creature to ever exist on planet earth is the blue whale. It’s much larger than any other creature that’s ever existed. And it exists right now and feeds on some of the smallest animals on earth: krill. > > Study up on physics and biology and get back when you have developed it further. Right now, your theory doesn’t hold up to basic facts. why would they be hundreds of feet tall to feed on plants that were 10 feet tall? ---
**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 13, 2013, 5:25pm UTC](https://boards.straightdope.com/t/why-did-the-dinosaurs-not-evolve-back/666138/23 "2013-08-13T17:25:28Z")
> [@aNewLeaf](#): > > Average size for dinosaurs was really small. No it wasn’t. No dinosaur was as small as many modern mammals. Even if you include birds as dinosaurs, the average size of non-avian dinosaurs was far larger than most modern birds. ---
**Author:** ![breakneck](https://avatars.discourse-cdn.com/v4/letter/b/e99b99/32.png) [@breakneck](https://boards.straightdope.com/u/breakneck)\ **Post date:** [August 13, 2013, 5:37pm UTC](https://boards.straightdope.com/t/why-did-the-dinosaurs-not-evolve-back/666138/24 "2013-08-13T17:37:05Z")
thank you for the replies and sharing information i wasnt aware of. i will do more reading to become beter educated on the specific eras thank you all ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [August 13, 2013, 5:45pm UTC](https://boards.straightdope.com/t/why-did-the-dinosaurs-not-evolve-back/666138/25 "2013-08-13T17:45:44Z")
> [@Stranger\_On\_A\_Train](#): > > The K-T event is neither the first nor more severe extinction event that has occurred in the history of the Earth; in fact, it was the last such major event of six or seven, and we are statistically overdue for another. I thought we were in the early stages or midst of one right now? ---
**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 13, 2013, 6:13pm UTC](https://boards.straightdope.com/t/why-did-the-dinosaurs-not-evolve-back/666138/26 "2013-08-13T18:13:58Z")
> [@bump](#): > > I thought we were in the early stages or midst of one right now? Extinction rates now are much higher than they have been in the recent past, mainly due to direct or direct human impacts, but aren’t close (yet) to the levels seen in the major mass extinction events in the past. Whether or not we reach them eventually may depend on how severe climate change and other effects become over the next couple of centuries. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [August 13, 2013, 6:20pm UTC](https://boards.straightdope.com/t/why-did-the-dinosaurs-not-evolve-back/666138/27 "2013-08-13T18:20:07Z")
> [@bump](#): > > I thought we were in the early stages or midst of one right now? I was distinguishing between the anthropogenic species extinction and those resulting from natural cataclysms. By paelontoligical standards, the current rates of extinction are currently less than what is estimated for historical biotic crises, but the _rate of increase_ of extinctions gives a trend that may be on par with events like the K-T or Triassic-Jurassic extinction event. And it should be noted that we are still actively classifying new species, so actual rates of extinction may be higher than observed. Stranger ---
**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 13, 2013, 6:21pm UTC](https://boards.straightdope.com/t/why-did-the-dinosaurs-not-evolve-back/666138/28 "2013-08-13T18:21:28Z")
> [@breakneck](#): > > why would they be hundreds of feet tall to feed on plants that were 10 feet tall? No dinosaur was “hundreds of feet tall.” [Sauroposeiden](http://en.wikipedia.org/wiki/Sauroposeidon), possibly the tallest, may have reached 56 feet. Many trees probably reached hundreds of feet tall in the Mesozoic, and it is speculated that tall sauropods used their long necks to browse on these trees. However, other sauropods probably browsed on low growth. Their necks in general were an adaptation for gathering food over a wide area with minimal effort, rather than for browsing tall trees. ---
**Author:** ![Great\_Antibob](https://avatars.discourse-cdn.com/v4/letter/g/e47c2d/32.png) [@Great\_Antibob](https://boards.straightdope.com/u/Great_Antibob)\ **Post date:** [August 13, 2013, 6:23pm UTC](https://boards.straightdope.com/t/why-did-the-dinosaurs-not-evolve-back/666138/29 "2013-08-13T18:23:57Z")
> [@breakneck](#): > > why would they be hundreds of feet tall to feed on plants that were 10 feet tall? Are you being entirely serious? No dinosaurs were “hundreds” of feet tall. The longest sauropods could probably have reasonably reached up somewhere under 100 feet, which is not a problem for most forests, including the forests that existed back then. ETA: along the same lines, why aren’t more current animals hundreds of feet tall to feet on trees? Why are elephants so large when they don’t need to feed on tall trees to survive. The size of the animal is not tightly correlated with the size of its food source. That’s true now, and based on everything we’ve discovered so far, it was true in the age of dinosaurs as well. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [August 13, 2013, 6:24pm UTC](https://boards.straightdope.com/t/why-did-the-dinosaurs-not-evolve-back/666138/30 "2013-08-13T18:24:36Z")
> [@Si\_Amigo](#): > > Compared to dinosaurs I would label them as medium-large sized animals and the ones we see today as medium-small. Huge yes, dinosaur huge, not really. The _Baluchitherium_ aka _Paraceratherium_, aka _Indricotherium_ weighed in at up to around 16 tons and 16’ tall. This comes in there with about the average dinos lumped as Brontosaurus . (I hate the term Apatosaurus, they can suck it 😛 ) Trust me, if you saw one of them lumbering towards you, you’d think it was a huge as a dino. ---
**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 13, 2013, 8:25pm UTC](https://boards.straightdope.com/t/why-did-the-dinosaurs-not-evolve-back/666138/31 "2013-08-13T20:25:54Z")
> [@breakneck](#): > > why would they be hundreds of feet tall to feed on plants that were 10 feet tall? The long-necked sauropods–that is, brontosaur type creatures–were only one type of dinosaur. And we think that only some of them used their long necks to feed on trees. Some of them used their long necks to stand still and eat acres of ground cover while only moving their heads. And have you ever been to a museum to see dinosaur skeletons? They were really big, but not hundreds of feet. We used to have the idea that the big sauropods were aquatic or semiaquatic like hippos, but now we know that they lived on dry land and ate land plants. As for the notion of yearly global floods, think about it. How does a polar ice cap form? When snow falls in the winter, and doesn’t melt in the summer. If the snow melts in the summer you don’t have an ice cap, you have winter snow. So even if there’s a lot of snow in one winter, you’re not going to have enough snow to lower global sea levels, and cause floods when that winter’s snow melts. And besides, the current evidence is that the world was generally much warmer in the age of Dinosaurs than it is today. That means that there were no polar ice caps–even at the north and south poles you’d have bare ground (or sea) in the summer. Dinosaurs lived in Antarctica, which was forested at the time. Sea levels were higher because of the absence of polar ice caps, what is now the American great plains was a shallow inland sea during the Cretaceous. ---
**Author:** ![Spectre\_of\_Pithecanthropus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/spectre_of_pithecanthropus/32/12343_2.png) [@Spectre\_of\_Pithecanthropus](https://boards.straightdope.com/u/Spectre_of_Pithecanthropus)\ **Post date:** [August 13, 2013, 8:48pm UTC](https://boards.straightdope.com/t/why-did-the-dinosaurs-not-evolve-back/666138/32 "2013-08-13T20:48:11Z")
IANA paleontologist, but couldn’t one reasonably argue that evolving into birds, as it were, was the long-term survival tactic of those small dinosaurs that survived the great extinction? Though early mammals were generally small as well, and primitive in comparison to their descendants, they must have been far better equipped to compete and reproduce. Developing feathers and taking to the treetops and the air was a good solution if the small-animal ground-dwelling niches were being taken over by mammals. Of course, I do realize that birds and mammals didn’t just appear at the end of the Mesozoic, so I’m not suggesting there was a simple changeover to mammals and birds at that point. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [August 13, 2013, 9:08pm UTC](https://boards.straightdope.com/t/why-did-the-dinosaurs-not-evolve-back/666138/33 "2013-08-13T21:08:31Z")
> [@Spectre\_of\_Pithecanthropus](#): > > IANA paleontologist, but couldn’t one reasonably argue that evolving into birds, as it were, was the long-term survival tactic of those small dinosaurs that survived the great extinction? Though early mammals were generally small as well, and primitive in comparison to their descendants, they must have been far better equipped to compete and reproduce. Developing feathers and taking to the treetops and the air was a good solution if the small-animal ground-dwelling niches were being taken over by mammals. > > Of course, I do realize that birds and mammals didn’t just appear at the end of the Mesozoic, so I’m not suggesting there was a simple changeover to mammals and birds at that point. Umm, no. Altho there is still some dissent on whether or not birds came directly from dinos (some think they just had a common ancestor), they split off around the late Jurassic, 160 some odd millions of years ago or about 100 million years before the KT event. The first “true birds” (and of course this is the subject of some disagreement) occurred about 120 mya. The KT event occurred about 66 mya. ---
**Author:** ![Rucksinator](https://avatars.discourse-cdn.com/v4/letter/r/898d66/32.png) [@Rucksinator](https://boards.straightdope.com/u/Rucksinator)\ **Post date:** [August 13, 2013, 9:17pm UTC](https://boards.straightdope.com/t/why-did-the-dinosaurs-not-evolve-back/666138/34 "2013-08-13T21:17:52Z")
> [@Si\_Amigo](#): > > … One is that some of them evolved into what we now know as birds; so they are really not “gone”. Monitor lizards are still around as well… Side question: I hear comments like the one above quite often, but I never hear people say that alligators or crocodiles, et al, are dinosaurs. Are they not considered dinosaurs? Or is it just so obvious that nobody (that I recall reading, anyway) mentions it? ETA: I did read this part below, but I wanted to ask anyway: “The only things that lived were things that were small and could burrow under debris and things that could live a long time without food (like crocodiles).” ---
**Author:** ![aNewLeaf](https://avatars.discourse-cdn.com/v4/letter/a/ac91a4/32.png) [@aNewLeaf](https://boards.straightdope.com/u/aNewLeaf)\ **Post date:** [August 13, 2013, 9:27pm UTC](https://boards.straightdope.com/t/why-did-the-dinosaurs-not-evolve-back/666138/35 "2013-08-13T21:27:17Z")
Dinosaurs were closer to birds than reptiles. They were an advanced branch that split off from early crocodiles, then developed warm-blooded metabolisms. ---
**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 13, 2013, 9:39pm UTC](https://boards.straightdope.com/t/why-did-the-dinosaurs-not-evolve-back/666138/36 "2013-08-13T21:39:24Z")
Define “dinosaur”. If you mean anything big and scaly and extinct, then crocodiles aren’t dinosaurs because they aren’t extinct. If you mean any organism that evolved from the last common ancestor of a sparrow and a triceratops (a common cladistic definition), then crocodiles aren’t dinosaurs because their ancestors had split off before that creature existed. The classic definition to qualify as a dinosaur you have to belong to the order Ornithischia or Saurischia, which are thought to be sister groups. And crocodiles are not part of either group. Check out this tree that outlines the current consensus view: [![](https://ucmp.berkeley.edu/museum/events/bigdinos2005/images/dino_tree.gif) ](https://ucmp.berkeley.edu/museum/events/bigdinos2005/images/dino_tree.gif) ---
**Author:** ![Rucksinator](https://avatars.discourse-cdn.com/v4/letter/r/898d66/32.png) [@Rucksinator](https://boards.straightdope.com/u/Rucksinator)\ **Post date:** [August 13, 2013, 10:44pm UTC](https://boards.straightdope.com/t/why-did-the-dinosaurs-not-evolve-back/666138/37 "2013-08-13T22:44:44Z")
OK. Thanks for the answers. But there is more ignorance to be fought… > [@Lemur866](#): > > … > Check out this tree that outlines the current consensus view: > [http://www.ucmp.berkeley.edu/museum/events/bigdinos2005/images/dino\_tree.gif](http://www.ucmp.berkeley.edu/museum/events/bigdinos2005/images/dino_tree.gif) The way I’m reading this chart it’s saying that birds evolved from theropods, who evolved from “(lizard-hipped dinosaurs)”; and not that they evolved from bird-hipped dinosaurs. Am I not reading this right? ---
**Author:** ![AndrewL](https://avatars.discourse-cdn.com/v4/letter/a/3d9bf3/32.png) [@AndrewL](https://boards.straightdope.com/u/AndrewL)\ **Post date:** [August 13, 2013, 10:56pm UTC](https://boards.straightdope.com/t/why-did-the-dinosaurs-not-evolve-back/666138/38 "2013-08-13T22:56:37Z")
> [@Rucksinator](#): > > The way I’m reading this chart it’s saying that birds evolved from theropods, who evolved from “(lizard-hipped dinosaurs)”; and not that they evolved from bird-hipped dinosaurs. Am I not reading this right? You are reading that correctly. Birds evolved from “lizard-hipped dinosaurs”. I suspect that the two branches of dinosaurs were named before it was known for sure that birds had evolved from dinosaurs, and the resemblance of the hips of “bird-hipped dinosaurs” to the hips of actual birds was coincidental or a case of convergent evolution. ---
**Author:** ![Rucksinator](https://avatars.discourse-cdn.com/v4/letter/r/898d66/32.png) [@Rucksinator](https://boards.straightdope.com/u/Rucksinator)\ **Post date:** [August 13, 2013, 11:56pm UTC](https://boards.straightdope.com/t/why-did-the-dinosaurs-not-evolve-back/666138/39 "2013-08-13T23:56:34Z")
Years ago I was looking through a book my nephew had on dinosaurs and it said that there were 2 types of dinosaurs: Those with a wish-bone, and those without. (I would not have been allowed to read a book that referenced evolution when I was a child.) I assumed that birds evolved from those with a wishbone, and when I saw that chart I assumed that the “-hipped” part referred to the wish-bone. (I really don’t know what the wishbone is.) Could someone clarify the wishbone thing? ---
**Author:** ![DrFidelius](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/drfidelius/32/3447_2.png) [@DrFidelius](https://boards.straightdope.com/u/DrFidelius)\ **Post date:** [August 14, 2013, 12:02am UTC](https://boards.straightdope.com/t/why-did-the-dinosaurs-not-evolve-back/666138/40 "2013-08-14T00:02:49Z")
Wishbones are fused clavicles (collar bones). [Previous page](https://boards.straightdope.com/t/why-did-the-dinosaurs-not-evolve-back/666138.md?page=1) [Next page](https://boards.straightdope.com/t/why-did-the-dinosaurs-not-evolve-back/666138.md?page=3)