i also think they are more specialized is there any scholarly articles that address this issue? maybe from ecology
Thermodynamics. Surface area available for dissipating waste heat increases as the square of linear dimension. Whereas the mass of tissue creating the waste heat increases as the cube of linear dimension. In other words, if an animal grows twice as large in any one dimension, it has eight times as much heat to dispose of, but only four times a much surface area. Eventually it reaches a point where it's difficult to maintain an efficient metabolism. There's a reason that the world's largest animals were reptiles. They're cold-blooded, meaning they don't generate internal heat. The only mammalian exceptions are the whales, and they live in an aquatic environment which very efficiently conducts and convects away their waste heat. Really big mammals like hippos and elephants spend a great deal of time either in the water or pouring water on themselves. During the ice age, mammalian "megafauna" did exist, but only in the coldest latitudes. Woolly mammoths and woolly rhinoceros were all enormously larger than their present-day cousins. Size is an advantage in freezing weather, and today the largest bears (polar bears) live in the arctic.
There's a book: "Why Big Fierce Animals are Rare". Library. One way to look at it: There's only so much life support available in a given area. You can make ten elephants with it, or ninety thousand mice. More likely, one elephant and 81 thousand mice. Dinosauers. Their actual coldbloodedness is up for debate - some definitely weren't, apparently. Many dinos had large sails or fins, huge flat crests and head ornaments, etc - there's been speculation (and data) that these things were for dissipating heat.
Very persuasive argument FR, thermodynamics definitely plays a big part. I wonder what the argument about environmental restraints would be.
and larger animals require larger habitats as humans destroy animal habitats the is more pressure on larger species so they die off quicker
They're faster and harder to kill. They can have more babies. They have shorter lifespans. They eat less.
No they weren't. Common woolly mammoths were probably a bit smaller than the Indian elephant on average (after all, they had less food available); only the more ancient Imperial mammoths grew considerably larger than modern elephants. Woolly rhinos were comparable in size to the living white rhinoceros, although their horn was certainly longer (if the species had survived until modern times, that horn would have become deadlier to its bearer than to any other animal.. Please Register or Log in to view the hidden image! ). Plus, there were also megafauna in the warmer parts of the World: like the giant ground sloths of South America and the diprotodon of Australia.
There is speculation that size is the reason that Neanderthals died out and us smaller humans survived.
You have a point. You can feed a lot more people with the meat from one Bison, than 1,500 mice, so hunt Bison.
That's true. But even without humans around, the larger habitat requirement would necessarily limit the numbers of larger animals. They simply require more food, more space, more water. Baron Max
According to this site, we're both right and wrong; http://www.science-spirit.org/archive_cm_detail.php?new_id=317 But I read a couple other websites that state different. One states that climate change did it. Another states a bunch of different shit: http://www.newscientist.com/article.ns?id=dn7221 I guess we'll never know! Please Register or Log in to view the hidden image!
They grew up to be very, very big. Not all of them, but many of them man. Please Register or Log in to view the hidden image! "The giant plant-eating Turiasaurus riodevensis, recently discovered in northern Spain, measured up to 120 feet (37 meters) in length and weighed as much as 48 tons, scientists say." Please Register or Log in to view the hidden image! http://news.nationalgeographic.com/news/bigphotos/15087612.html Please Register or Log in to view the hidden image!