why did the dinosaurs not evolve back? why were they so massive? does that mean the plants they fed on were massive too? why didnt the large plants re evolve ? why were they so large ? I have a theory about this and i wanted to see if i was anywhere close. ok the dinosaurs went extict because the metoer that impacted the yucatan penn. . The dinasurs were so large because the plants they ate were too . why? well before the major impact i think the earhs axis of orbit was something much different . Because of this the ice caps would have melted and refroze every half year making ocean levels rise and fall hundreds of feet. so plants adapted to this at least species in lowlieing regions by being very tall with tough bark stems and strong roots like seaweed and soft fiolage on top so they could survive the floods the dinosaurs were huge in high to be able to feed on these and keep heads out of the water . the smaller creatures would run for higher grounds as well as the smaller meat eater dinosuares that fed on them and the floods would reside and the cycle would repeat. then metorite hits kills of dinosuars , changes earths axis to wheere it is now . no floods . no need for plants to adapt . no need for dinosaurs to adapt. i would like to know the real answer to this question thank you for your time
Welcome. Good question.
thank you i hope there someone to shed some light on it im very excited to know
They didn’t evolve back because they evolved forward and became birds, some of which were pretty big . Not dinosaur big, but bigger than people.
After the extinction event, competition went in a different direction, and intelligence became a major factor in the predator-prey race.
Is my opinion.
The dinosaurs did “evolve back”, if by that you mean “evolve to smaller size”. The largest dinosaurs alive today max out at about 150 kg, and most of them are less than a kilogram.
You’ve got to understand how evolution works. It’s not a choice between evolving or going extinct: In fact, extinction is one of the major mechanisms by which evolution works. At the end of the Triassic era, you had a wide variety of dinosaurs, some huge, some small. Then the environment changes, in such a way that being huge is suddenly a disadvantage. All the huge dinosaurs die off, but some of the small ones survive. Now all of the dinosaurs that are left are small.
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.
There are likely a few “real” answers and and boatload of speculation. 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. If you are asking why we don’t have large land animals roaming the planet anymore it may be because the climate changed enough that it couldn’t support the development of the old order and that smaller mammals were able to develop to a point that they successfully kept them from redeveloping.
There were very large mammals in North America until humans arrived. Giant Sloths, Uintatheres, all kinds of huge crazy animals.
Please try using paragraphs and capitalization. It makes reading your questions much easier.
The environment that they evolved in had changed. There were different conditions, different food sources, and different competitors. And as already said they evolved right along with the different conditions and we see them today as birds.
The evidence doesn’t support this, and ice caps don’t melt and refreeze that quickly.
Plants during the age of the dinosaurs were no larger than the largest modern ones. During the Mesozoic there was a shift in dominance between gymnosperms (conifers and others) and angiosperms (flowering plants), but this happened in the Cretaceous, in the middle of the dinosaurs’ dominance.
It’s an open question of why dinosaurs got so much larger in the Mesozoic than mammals did during the Tertiary. Changing levels of carbon dioxide (which could have increased plant productivity) or oxygen (which could have permitted greater activity) could have had something to do with it, but these changed throughout the Mesozoic and this can’t be a general explanation.
Sauropods may have been able to get so big because of their highly efficient feeding apparatusand their physiology. Mammals by happenstance have not been able to duplicate this system. The largest carnivores may have evolved to exploit the large sauropods. Dinosaurs in other groups were generally within the range of size reached by the largest mammals, such as Paraceratherium (Indricotherium).
The asteroid strike that killed the dinosaurs did not change Earth’s axis. The most recent ice ages did not start until about 2 million years ago, most likely due to changes in oceanic currents triggered by the closure of the isthmus of Panama. There were no ice caps on Earth at any time during the time dinosaurs were dominant, although there had been ice ages before dinosaurs evolved.
If any floods would have yearly covered the earth, we would have seen that in the fossil records. You can tell if a soil is dry land, marsh-like, a lake, shallow sea, a sea with big fluctuations, or deeper sea. You can tell by the tiny fossils of plants and animals that drift down and make up the soil.
Your scenario of big floods every half year has never been found anywhere.
As for the larger size of insects, that has been linked to the higher levels of oxygen in the air. As Colibri said, the largest tree-like plants back then were the same size they are now.
I don’t know anything offhand about biannual flooding, but I’m sure they would have seen something like that in the fossil record if it really happened. (and it seems unnecessarily complex).
As I understand it, the main reasons dinosaurs got so big were 1) they could, and 2) keeping up with the Joneses.
They could grow big because their hollow bones had good strength for their weight, and because (unlike lizards and amphibians) their legs were positioned directly under their mass, which helped support their weight better. Earth’s higher oxygen content may have played a part too.
The most likely reason they did grow big was because of competitive advantage with each other. Really big animals are relatively safe from predation – even huge predators will hesitate to fight something that can hurt them back. Current evidence implies individual dinos grew really fast – they were probably racing to get big enough to deter predators.
Regarding “evolve back” – evolution is not directional; there’s no forward and backward. Furthermore, it’s not purposeful – creatures don’t evolve for a purpose. It’s more a process of elimination; some of them die and some don’t. A change in conditions that kills some of them before they pass on their genes but permits the survivors to pass on their genes can lead to the evolution of a new species…IF the survivors survived because of some heritable trait, not just random luck.
Some dinos did survive. Birds are dinosaurs – most likely they survived because they were small. Apparently, when the Chicxulub meteor hit, every land animal on earth heavier than twenty pounds died. All of them.
While it’s true that famine (presumably from an “impact winter”) hits large animals harder than small ones, the speculation I’ve heard that makes the most sense to me is that large animals do not tend to burrow (too much work). The meteorite is widely believed have set off worldwide fires, and some experts have said it set earth’s atmosphere on fire; burrowing only a few inches underground would have protected an animal from this heat. it may be that ONLY burrowing animals survived (and of course some sea life, although sea life in general also took a big hit).
Some birds burrow today (burrowing owls, for example) and thus might have lived to “radiate” out into all the birds we know today.
I read the OP as asking why dinos have not evolved “back” to their pre-extinction numbers and variety, based on the few surviving species (not backward evolution). I think the emergence of the mammals exploiting previously occupied niches created competition where there was none before - which prevented re-emergence of large dinosaurs.
My other thought is that the dinosaurs have been gone for only 65 MY, but they existed from about 250 MY ago up until then. Give it some more time and we may see something like them return, depending on how well they compete.
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.
First of all, it wasn’t just dinosaurs which experienced extinction around the Cretaceous-Tertiary (K-T) boundary; nearly all large animals across the entire kingdom went extinct over an approximately 800,000 year period. There is some evidence that mass extinctions were occurring even before the date of the bolide impact at Chicxulub (and similar large impacts in other locations), and extinctions continued to occur long after the transient climate conditions from the impact should have subsided, indicating that there were more factors than simply dust or soot occluding sunlight. 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.
Second, dinosaurs didn’t “evolve back” because evolution doesn’t work that way. Although there are sometimes a tendency for highly divergent species or even clades to evolve similar mechanisms such as eyes (referred to as convergent or parallel evolution) there is no directed flow of development in evolution, and phenotypical characteristics are selected based upon the ultimate reproductive fitness of the carrier. Evolution sometimes produces regressive phenotypes, such as cave fish losing eyesight, but there is no directed change or modification to return to a particular state, and the record is rife with examples of different species evolving wildly different mechanisms to adapt to similar conditions.
Although we generically lump the dinosaurs into a single clade, Dinosaura, a more careful examination of fossil evidence indicates that there was enormous diversity in basic characteristics such that if we were starting to classify them today we would divide them into separate clades. One particular group of dinosaurs which survived the event and evolved into modern Aves (birds). Others declined precipitously and their ecological niches replaced by presumably more adaptable mammals. Specifically while mammals took over and grew to such enormous sizes (most of the mammalian megafauna have subsequently become extinct or were hunted to extinction) is a point of active research and debate. Very large animals do have some significant advantages in terms of competition and protection from predation, but also come with an evolutionary cost that would seem to be prohibitive, so exactly how they evolved is not well understood.
There is no indication that a bolide impact shifted the Earth’s axis significantly, and in fact an impact with sufficient force to do so would likely cause the mantle to erupt over the entire surface of the Earth virtually wiping out all life. The rotational characteristics of the Earth do change over time (by approximately 1° per million years) but there is no indication that it has shifted by such dramatic or rapid change in the geological history since the Cambrian Explosion. It is more likely than an impact or some other event would disrupt ocean currents which would in turn alter the climate of the Earth.
There are a large number of holes in the hypothesis of the o.p., but rather than address them in detail I would recommend obtaining a more thorough layman’s knowledge of paleontology and evolutionary processes. The popular science works of the late paleontologist Stephen J. Gould (Ever Since Darwin, The Structure of Evolutionary Theory, The Richness of Life, Ontogeny and Phylogeny) is an excellent place to start learning about the depth and breadth of evolutionary theory and paleontology.
Stranger
Blue whales are more massive than any dinosaur that ever lived. There is a reasonable case for a dino that is as long or longer than a Blue Whale.
Average size for dinosaurs was really small.
Well I didn’t consider surf vs turf. 
One reason we know there wasn’t periodic flooding caused by the melting ice caps is that at times there wasn’t any polar ice. Throughout most of the “dinosaur” era, the earth’s average temperature was around 20 to 22 deg C, significantly warmer than it is now (about 14 deg C).
65 million years ago, a hunk of rock slammed down in southern Mexico hard enough that debris from the impact landed as far north as Tennessee and Kentucky. All around the world there’s a layer of carbon from the event, indicating that the entire world burned. 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).
After that, the world went through a cooling phase, eventually dropping all the way down to an average temperature of 12 deg C or so. This is a drastically different climate than what the dinosaurs evolved in, which is why dinosaur-like creatures didn’t evolve as the earth recovered from its extinction event as they had after previous extinction events.
While the K-T extinction gets the most focus in schools and elsewhere, it is far from the only extinction event that the earth has faced. Each extinction event has made drastic changes to life on earth. It’s just that in all of the previous ones, you had dinosaur-like creatures before the extinction and dinosaur-like creatures evolved to replace them after the extinction. If you take a closer look at what was alive during those times though, you can see that there were pretty drastic changes during those other extinction events as well.
How species evolve is due to millions of factors. If you were to start with two planets, identical in absolutely every respect, plunk a proto-dinosaur pair on each, the chances are they would evolve with major differences between each planet’s animals.
It’s a little like the “butterfly flapping its wings in Brazil causing a hurricane in Florida.” Ecological systems are chaotic and impossible to predict over long periods of time.
So even if the planet was the same when 98% of the dinosaurs were extinct as 100 million years before (it wasn’t), the chances of the remaining 2% returning to their roots is highly unlikely.
This principle explains why we have such a diversity of life. Even though all life may have come from one original organism, no two species evolve in the same way, and over time, become more divergent.