The dinosaurs were wiped out by a catastrophic event, not by a lack of adapted traits. So why is there not anything as big as the larger dinosaurs today? I want to know why there is a definite lack of huge reptiles (or huge anything–save for elephants and whales) stomping around.
Specifically, what changed in the Earth’s environment that precluded the re-evolution of dinosaurs or other very large animals from recurring?
Big animals need lots of food. In the days of the dinosaurs, there were a lot more plants.
There are a lot of large species remaining – principally in Africa and in southern Asia.
Impacts resulting from climate change, the spread of a competitive species, etc., can wipe out a megafauna and have done so several times in the past. The most recent event of this sort was towards the end of the Ice Age – in the period 25,000 to 10,000 years ago, the greater number of the world’s large animals became extinct. We’re in the process of recovering from that at present – much like the earliest Triassic and Paleocene, large animals are scarce.
Your question doesn’t really make much sense.
The blue whale is the bigest thing (that we know of) that ever lived. Bigger than any dinosaur.
Why ask “(or huge anything----save for elephants and whales)”, when elephants and whales are the hugest things around today?
My last sentance could have been worded a bit better.
It sounds like you’re asking, “why aren’t there huge things, (apart from the huge things)”.
actually, there are a lot of factors when deciding how big an animal can potentially get. food is one, but available oxygen is another (as in insects). sure oxygen levels as is are more than adequate for an insect one or 2 inches big, but the same insect at 20 feet tall would need substaintally more.
available living space can also hinder growth. if you spend most of your time underground, or in a tree, evolution is going to keep you small.
The amount of protein in your diet also has something to do with how large you can become.
Dem-- I think the Q is, “why aren’t there nearly as many huge things now as there have been in the past?”
Just so happens that before coming on-line I had just put down a book by E.O. Wilson titled The Diversity of Life. Here is a quote from that book I read not 10 minutes ago -
Whales, elephants, rhinos, hippopotami, giant squid, giraffes, anacondas, whale sharks, …
I guess the only thing (size-wise) we’re lacking is land animals in the sauropod range.
Weren’t mammals evolving in the direction of gigantism before man the hunter arrived and wiped most of the large species out?
Non-human predation would seem to favor evolution of ever-larger animals, since a predator isn’t likely to attack an animal big enough to seriously injure said predator. Unless the predator evolves to be larger…and so on…
Can’t find a cite right now, but I had read a theory that suggested that humans were the reason for the extinction of many larger animals, at least in North America. They were apparently tempting hunting targets.
Just 15,000 years ago there were many more large mammals. North America was drastically different…giant ground sloths, giant running bears, mammoths, mastodons, giant glyptodons, steppe bison, two species of musk oxen, saiga antelope, sabertooth cats, dirktooth cats, lions, american cheetahs, camels, horses, dire wolves, giant badgers, giant beavers, giant wolverines. Many of our current large mammal species were larger during the Pleistocene. Or perhaps it is more proper to say that many large mammal species exist today only in dwarfed forms.
Compared to the Pleistocene, our current mammals are smaller and less diverse. Coming into an interglacial period like we are in now probably hit them hard, but the Pleistocene is full of interglacial periods and the megafauna survived them. Some combination of rapid climate change combined with human pressure are the current theories, although it is controversial which should be given more weight.
here is some illustrated material that compares the larger dinosaurs to today’s beasts. No land animal today is remotely close to the size of a brachioasaurus.
I have often wondered why scientists are so tentative about naming humans as an almost certain cause. Too many coincidences, even in the relatively modern era (700 AD or so) the Moa (gaint, flightless bird) went extinct just as the Maoris arrived in New Zealand. Seems to happen again and again.
It seems that you are really aksing “why were the dinosaurs so big”, rather han why there are no bog creatures today. As other shave pointed out, we do have big creatures today. Before the arrival of man every continent teemed with huge mammals. They all disappeared slightly after humans arrived. That seems to be the most liely answer to your quetsion. We don’t have big animals because people find them very easy to eat, and becase big animals have a very hard time coping wiht the rapid environmental change produced by people.
Now if your question is 'why didn’t mammals ever reach the size of the larger dinos before the arrival of people, that is another question, and it is really just ‘why were dinos so big’ rephrased. Dinosaurs were atypical. No land creatures before or after them ever recahed the same size. It is the dinosaurs that are odd, not the mammals.
Politics in at least some cases. If the ‘native peoples’ have wrought massive environmental damage and if the 'natural environment is no more natural than a cornfield, then the case for both environmental legislation and indigenous rights are thought by some to be weakened. They aren’t of course, but it does become much more complex, and complexity is rarely seen to be a good thing in politics.
I believe that this has been proposed by reputable scientists. I am trying to remember the book in which I read this, and I think it may have been the well-known “Guns, Germs and Steel” by Jared Diamond. Whoever it was, he also cited the extinction of most large mammals in North America shortly after the arrival of homo sap. The large mammals in Africa escaped extinction because they evolved alongside of humans; The only ones that survived were those fierce or skittish enough to escape the skilled and spear-carrying predator. Many in Eurasia survived longer because the large east-west land mass along a common latitude gave them someplace to escape to. In the islands and the continents with north-south axes, they had less room to escape.
Wait a minute, Blake. If we are talking about vertibrates (and I assume we are), we only have reptiles, mammals, and birds. You seem to imply that there are many other choices of land vertibrates of which reptiles are only one.
I know you said “dinos” and not “reptiles” but dinos are just a subset of reptiles as elephants and whales are a subset of mammals.
As has been pointed out, the post-Cretaceous land animals just haven’t been as big as the dinosaurs. The question is why. I can’t think of any answers that make sense.
The closest I can come is that it takes a certain amount of time for evolutionary pressures to drive large herbivores up to sauropod sizes. Maybe the African and American megafauna were headed for sauropod and carnosaur sizes, but they just didn’t have time enough what with the ice ages and then humans wiping them out. Now it’s all they can do to stay alive anywhere, what with poachers and development.
IIRC there were several waves of dinosaurian evolution, with each new wave bringing along a larger megafauna. But I’m not sure. T-rex and brachiosaurs were Jurassic animals, not Cretaceous. And the Jurassic was the middle period of the dinosaur era, not the last one. I think the dinosaurs were around for 225 million years, so they had more time overall to evolve, but did it take all that much time for the dinosaurs to evolve to large size? How big did the camarosaurs start out, and how fast did they get to brontasaur (excuse me, apatosaur) size?
I dunno. But an interesting question.
Doubtful. At least with regards to the Mammoth/Mastadon extinctions. A friend of mine is a Paleo-Indian archaeologist and says there are only a handful of finds that show conclusivly that they had been hunted by humans. I’d have to check with him on the evidence regarding scavaging of the beasts. The drastically changing environment from the end of the ice age is a more likely culprit.
Of course humans showed up here as the ice was retreating and the climate changing.