If birds were once dinosaurs, then why dont they dominate the planet today? The vast majority of bird species are just small flyers who eat bugs and small animals. You dont see giant grazing birds or large bird carnivores anymore (though there were some not too long ago, as in the terror birds). Why dont you see birds today that are like the raptors (as in the dromaeosaurs). Why have the never re-evolved the features that some dinosaurs had? A raptor-like bird isnt really out of the question, considering the relatively recent terror birds, who only went extinct like 2 million years ago (more than 60 million years after the dinosaurs died out), if i’m not mistaking.
Yeah, you have some large birds like ostriches and emus (who are probably the most dinosaur-like birds that exist today), but all the large carnivores on this planet are mammals (lions, bears, tigers, wolves), with the exception of crocodiles and komodo dragons. There are no large carnivorous birds anymore. Come to think of it, reptiles are mostly small animals too. The only giant-sized animals since the dinosaurs vanished have all been mammals. Why can’t birds achieve the sizes of the dinosaurs, or fill the same niches as the dinosaurs once did?
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Why Are Birds So… Undiverse As Far As Survival Tactics Go?
Posted on August 20, 2012.
“Why are birds so… undiverse as far as survival tactics go ?”
They are not. The bare fact of 10,000 extant species, each with their own niche is testament to this. A niche is a collective range of survival tactics, to use your wording. Survival in practice means finding ways of staying alive and by extension, striving to reproduce. A niche, in other words. That they are ubiquitous in most terrestrial areas and found over and on water too is further confirmation of their wide-ranging success.
“If birds were once dinosaurs, then why dont they dominate the planet today ?”
Birds evolved from dinosaurs, indeed they are considered dinosaurs by some quarters. A catastrophic extinction event occurred about 65 mya that all but finished the dinosaurs off. Now, early mammals had already come on the scene when dinosaurs prevailed, they coexisted for a long time. They were mostly small and secretive, playing out a discrete nocturnal existence in the shadow of their formidable neighbours. When this extinction event was all said and done, there were many available niches left to fill, those left behind by the dinosaurs. Birds also coexisted with dinosaurs (or ‘other’ dinosaurs). They branched off on their own evolutionary path and took to the air. As the dominant ground dwelling animal, the mammals naturally radiated out to fill said niches and diversified vastly into all (eventually) that we see today. They became the dominant group on land, birds, the sole dinosaur survivors, were already taking to the skies. This is not to say mammals dominate the planet, far from it, I am just explaining why birds do not dominate land.
“You dont see giant grazing birds or large bird carnivores anymore………”
Read above, large carnivorous niches were filled by mammals.
“Why have they never re-evolved the features that some dinosaurs had ?”
Evolution does not, and cannot plan and foresee the future. Birds had already diverged on their evolutionary path. Some of the features you are surely talking about (huge teeth, claws etc.) were features evolved by mammals to deal with the emerging mammalian herbivores. Again, the niches that could have made use of such characteristics were taken.
I think the above answers your second paragraph.
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Cal – I have read several of your previous answers that promote the view you present here regarding bird evolution. I find it disingenuous that you state so confidently your position as though it were close to unchallengeable fact. Indeed, yours is a minority hypothesis within the biological and paleontological community. The overwhelming consensus among the experts, and that is certainly not me, is that birds evolved from a theropod ancestor. Something you know very well (as an alternative point of view that is, not as a fact in your eyes).
You also seem to be doing something similar in brushing aside the idea of endothermic dinosaurs. This, despite the relatively recent insights and research that may show endothermy in at least some dinosaur lineages. More generally, there may well have been a spectrum of homeothermic physiology utilised by some species.
My point in these observations is to highlight the cavalier attitude you have when it comes to these 2 concepts. Really, you are acting with disingenuous disregard for the bigger picture and consensus view.
Birds almost certainly did not evolve from a dinosaur. The most likely ancestor of birds is a small reptile that lived in the trees and glided. There are a number of gliding reptiles in the Mesozoic, and most of them glided with pieces of skin that were stretched between different body parts. Only one of these gliders had feathers. This feathered glider was Longisquama insignis, which lived in Central Asia in the late Triassic, some 75 million years before Archaeopteryx. A fossil feather that resembled Longisquama feathers, but dated later than Longisquama, is named Praeornis. Praeornis is also found in Central Asia. That shows that feathers like those found on Longisquama persisted and evolved.
That said, birds did escape the end of Cretaceous extinction that killed all of the dinosaurs. However, birds did suffer major losses as well. The dominant land birds of the Mesozoic were the enantiornithine birds, which were also completely wiped out. Not a single species of enantiornithine birds survived. The only survivors were the shorebirds, which belong to the same group as all living birds. If we count diversity, or how many species of birds, then birds are not “undiverse” at all. There are about 10,000 species of living birds, but only about half that many species of mammals. Reptiles and amphibians are not more diverse either, because there is no single group of reptile or amphibian that has as many species as the birds. In fact, the turtles and crocodilians are the least diverse among reptiles, besides the tuatara, which is limited to one of two species.
If you are measuring disparity, however, the mammals do seem to be more disparate, as there are mammals as small as a Naked mole rat and as large as the blue whale. There are flying mammals, gliding mammals, bipedal and quadrupedal mammals, and even mammals that have no hindlegs. There are naked mammals, but hardly any birds that have no feathers. Nevertheless, some birds did evolve gigantism and they apparently did fill the niche left by the meat eating dinosaurs. They were the terror birds, which survived until a couple million years ago, not long after the great faunal interchange between placental mammals from Asia and the marsupials from South America. The terror birds may have been outcompeted by the stronger and faster carnivores such as the big cats. The reason birds cannot achieve the size of, say, T. rex, is because they are endotherms. The larger an animal is, the smaller the amount of surface area in proportion to its volume. That means large endotherms like birds and mammals have more trouble losing heat than small ones. That works out great for the emperor penguin, because it can survive in the Antarctic, while its smaller cousin, the king penguin, cannot. But this limitation means that birds simply cannot become too large or else they could easily suffer heat strokes, unlike the ectothermic dinosaurs. Of course there are paleontologists who romanticize about “warm-blooded” dinosaurs, but they do that when they are not wearing their thinking cap. Instead, they are wearing dunce caps when they think that dinosaurs were endotherms.
Perhaps the main reason birds have not been able to evolve as wide a range of body forms as mammals is because they are way too specialized. All birds, for example, are bipeds by the time the dinosaurs became extinct, and all of them had hands that were tied up in a pair of wings, and all of them had thighs that are fixed in place so that they can breathe through their air sacs. Therefore evolution simply had fewer options and less room to work with when dealing with a bird’s body than with a mammalian body.
The last dinosaurs who died closest birds was the Terra bird about the size of an ostrich or emu, and these small meat eating birds about the size of a weaver bird. It is believed there were no flowers or mammals back then when the dinosaurs were around. Without flowers no fruit, without fruit no seeds for the birds so they had to eat something. Mammals are able to adapt faster than any animal except for fish. Plus we would die out long long before birds will because even though we adapt faster they are able to adapt to to things we can’t adapt to.