lots of plants
July 31, 2006 8:10 AM   Subscribe

back when the world was relatively new, it seems like the world could support much much more life. why not now?

im not talking about time since industrialization and the impact of humans/fossil fuels.

have a look at this guy >> http://news.nationalgeographic.com/news/2006/07/060728-giant-dinosaur.html
(115 to 131 feet (35 to 40 meters) long and weighed between 88 and 110 tons (80 and 100 metric tons))

now imagine a pod of these guys, eating their weight in vegitation each day. How was the planet able to replace that much vegitation? Everything was bigger too - foot long mosquitos etc.

from what i understand, animals which arrive on an island slowly shrink because the scant available resources favor animals who consume less. I can only conclude that the immense size of the old animals were enabled by *INSANE* amounts of resources.

since the meat eaters eat the plant eaters, and the plant eaters eat the plants, i guess my question is: what was so fundementally different that allowed plants to thrive to this degree?
posted by Tryptophan-5ht to Science & Nature (17 answers total) 2 users marked this as a favorite
I'm not a palentologist or a geologist, but the temperature could have been higher, humidity could have been higher and there could have been more CO2 in the atmosphere, all of which would probably accelerate the growth of certain kinds of plants.

My museum trips lead me to believe that the plants that grew when dinosaurs were areound were different than what we see today.

Alternately, if you believe Larry Niven, it's because The Magic Goes Away.
posted by GuyZero at 8:30 AM on July 31, 2006

Dr. Octave Levenspiel did research into atmospheric pressure during the mesozoic age, noting other research that suggested levels of carbon dioxide were several hundred-fold higher. In addition to "air" pressure having a theoretical affect on animal physiology, it could have conceivably provided the atmospheric constitution for terrestial plant life to flourish.
posted by Blazecock Pileon at 8:31 AM on July 31, 2006

I'm under the impression (perhaps mistaken) that the entire global climate was different then. Different species of plants grow at different rates, and I guess a lot of the species that thrived under that climate were very quick at replacing biomass?

Perhaps global warming will eventually be self-correcting because higher temperatures and CO2 concentrations will result in a greener Earth. Of course, humans may well be extinct by then, but that's how things go, I guess.
posted by JMOZ at 8:32 AM on July 31, 2006

Also, there were more large mammals around fairly recently in earth's history (example) until humans showed up to kill and eat them. We're quite good with teamwork and weapons.
posted by clarahamster at 8:39 AM on July 31, 2006

Two things to consider:

First, dinosaurs and other pre-Cenozoic animals were HUGE, but there were relatively fewer of them, by all accounts I've heard. The lower number relieves some of the perceived stress on the environment. Plants themselves were also much larger, too.

Second, what came after the mass extinctions 65 mya is all predicated on what survived the extinctions. The ancestral mammal, pater familias to everything from us to monkeys to dogs to bears to cows to lions to etc, was a small rodent-like creature, about the size of a rat or squirrel. Some large mammalian Pleistocene megafauna that evolved from this ancestor existed as recently as 10-20 thousand years ago, but they died out due to uncertain factors (some think overhunting by humans, others disease, others climate change, etc etc), so we have no idea as to a limit to their size. They only had ~65 million years to evolve to the sizes they were at the time of extinction, as opposed to nearly 200 million years in which dinosaurs evolved if we assume they "began" at the Permian-Triassic transition.

The point is not that megafauna could not exist in today's environment, it's that there just simply are not any in existence due to both genetic and epigenetic factors.

On preview: I really have to take issue with ClaraHamster's proposal of humans causing the New World megafauna to die off. The timing of human movement into the New World just doesn't jibe with the timing of the extinctions.
posted by The Michael The at 8:44 AM on July 31, 2006

from what i understand, animals which arrive on an island slowly shrink because the scant available resources favor animals who consume less

I recall from that most great authority, David Attenborough shows, that it goes the other way. Island animals tend toward giantism. IIRC in no small part because of reduced predation, which allows them to get big and clumsy.

For warm-blooded animals anyway, larger animals are more efficient. An elephant eats less than an elephant's-mass of mice does, because it has less work to do keeping up its internal temperature as its surface area/mass ratio is lower.

I am not a biologist of any kind. I certainly don't know if anyone has attempted to guesstimate the total biomass of Earth at different points in history.
posted by ROU_Xenophobe at 9:59 AM on July 31, 2006

The kinds of huge dinosaurs you're talking about died out in the early Cretaceous period, about the time the big bipedal carnivores appeared.

You find that kind of thing again and again in the history of life. So the reason why there aren't any huge creatures now is because mammals make such good predators.

[And just in passing, the largest animals who have ever lived, completely dwarfing the largest dinosaurs, are alive now.]
posted by Steven C. Den Beste at 10:12 AM on July 31, 2006

Blue whales don't count. Well, ok, I'm assuming the OP meant land animals. I mean, anyone could get huge if bouyancy meant you were essentially weightless and you were immersed in food twenty-four hours a day. That is so totally cheating.
posted by GuyZero at 10:36 AM on July 31, 2006

Warmer and wetter. Better for plant life, therefore better for the beasties. More of the biomass was on the surface, instead of being burried deep underground, slowly being changed into oil.
posted by blue_beetle at 10:50 AM on July 31, 2006

I'm curious whether there might be a temporal component to this. Dinosaurs were around for over 200 million years, and generally grew bigger and bigger over that time. I think the big Pleistocene mammals followed a similar pattern. Perhaps it just requires a lot of time for big animals (who tend to be much more delicate and fragile per pound) to evolve, and since they are usually the first ones to go when conditions change, they only appear after long periods of environmental stability.
posted by bjrubble at 11:28 AM on July 31, 2006

We're in the middle of a global cooling period -- for a large portion of the earth's history, there have been no glaciers. The most recent ice age reached its peak about 13,000 years ago and has been receding ever since. We're helping to speed that up. When dinosaurs were around, the earth was warmer, and the land mass (pangaea) was closer to the equator. As you may have noticed, equatorial ecosystems provide quite a bit more biomass and diversity than do polar ecosystems.

"On preview: I really have to take issue with ClaraHamster's proposal of humans causing the New World megafauna to die off. The timing of human movement into the New World just doesn't jibe with the timing of the extinctions."

Perhaps you could point to some documentation of this. One can grudgingly accept that there is a debate as to whether humans had an influence on the disappearance of megafauna worldwide, but it's hard to overlook the speartips found in the fossils of mammals in North America, or the fact that the great animal extinctions seem to occur very close to the estimated arrival time of humans, from the South Pacific (50% of bird species just happen to disappear as humans appear on each of the islands) to North America, to South America. Granted, the climate changed at the same time (allowing for human migration), thus perhaps putting strain on colder-climate animals (wooly mammoths), but the plains animals in North America differ from plains animals of central Africa only in their lack of co-evolution with humans. In my mind, the debate is over. But I hear there are some old-school scientists who won't accept it.
posted by one_bean at 11:57 AM on July 31, 2006 [1 favorite]

BJRubble, the dinosaurs didn't grow larger and larger the entire time they existed. The largest dinosaurs lived during the Jurassic. At the end of the Jurassic, the Allosaurs appeared, leading to a long and successful line of big bipedal predators, and after that the size of the largest dinosaurs got quite a lot smaller.

At the end of the Cretaceous, there were three main strains of large herbivorous dinosaurs: the ankylosaurs, the duckbills, and the ceratopsians. None of them were remotely as large as the big sauropods like apatosaurus.
posted by Steven C. Den Beste at 11:58 AM on July 31, 2006

One_bean, there have been other cases of mass exitinctions of large fauna which weren't related to humans, though I have no doubt at all that humans were responsible for quite a few.

One of the really big ones happened when plate tectonics finally created a land bridge between North America and South America. At that time there were a lot of big ground-living herbivores in South America, but little in the way of big, efficient predators. North America had a plentiful supply (particularly big cats) and once there was a way to get there, they laid a bloody swath through the South American fauna, making all the big ones extinct.

(Of course, South America got its revenge by sending possums and armadillos north. So there.)
posted by Steven C. Den Beste at 12:04 PM on July 31, 2006

This was just mentioned in a book I read...what book...thinking, thinking...it might have been "Is the Temperature Rising? The uncertain science of global warming" by George Philander, or it might have been some other book on climate. But I was interested to learn that one reason there were so many huge insects in prehistoric times was that there was a lot more oxygen in the atmosphere, which made it possible for even animals that are not efficient at pulling oxygen out of the air (like bugs) to grow really big.
posted by not that girl at 2:06 PM on July 31, 2006

From Discovery Channel:
In the past, researchers have assumed that the 35 percent-oxygen atmosphere of the Carboniferous Period (compared to today's 21-percent oxygen) made it easier for insects to get bigger. But the size and the oxygen levels may not be related, he said.
Somehow high oxygen may allow animals to get bigger but I don't know by what mechanism.
posted by MonkeySaltedNuts at 2:21 PM on July 31, 2006


2003 Grayson DK and Meltzer DJ. "A Requiem for North American Overkill." Journal of Archaeogical Science 30: 585-593. [link to PDF]

from the article: "Yet despite this popularity, Martin's position [the overkill hypothesis] gains virtually no support from the North American late Pleistocene archaeological and paleontological records. As a result, it gains almost no support from the scientists who specialize in these records. Here, we provide a brief historical background to Martin's argument, and then turn to the empirical record that shows it to be incorrect." (p. 585)

It's quite the opposite from how you characterize it, actually. Overkill was first theorized in the 1860s, was formally formulated by Martin in the 60's, and now it's the old school archaeologists that refuse to give it up. I'm the last person to want to resort to argument by authority, but Grayson and Meltzer aren't exactly no names in the field, either.

Fiedel and Haynes respond:

2004 Fiedel S and Haynes G. "A Premature Burial: comments on Grayson and Meltzer's 'Requiem for Overkill'." Journal of Archaeological Science 31: 121-131 [link to PDF]

and Grayson and Meltzer counter:

2004 Grayson DK and Meltzer DJ. "North American Overkill Continued?" Journal of Archaeological Science 31: 133-136 [link to PDF]

Much of both is typical archaeological-article posturing and name-calling, but Grayson and Meltzer's arguments are, for my money, on the mark. The "speartips found in the fossils of mammals in North America" that you reference refer to a dozen or so Clovis sites with mammoth remains. Most megafauna species were long gone by the time Clovis begins. Pre-Clovis occupation and hunting are a definite possibility, but we're going to need a hell of a lot more evidence of big game hunting than a few possible sites (Monte Verde, Meadowcroft, Topper) with crude tools.

Some other things to read:
Survival by Hunting by George Frison, about the realities of early hunting endeavors.

2004 Schurr TG. "The Peopling of the New World: Perspectives from Molecular Anthropology." Annual Review of Anthropology 33: 551-583 [link to PDF] A good review of current molecular and archaeological evidence for New World migration. I couldn't tell exactly, but it seemed like you were indicating that the peopling of the New World came from the Pacific Islands, which is not likely the case.
posted by The Michael The at 2:30 PM on July 31, 2006

No, merely that a totally separate (and much later) human migration out through the islands of the South Pacific resulted in the exact same thing: complete destruction of non-human animals.

Thanks for the references.
posted by one_bean at 10:38 PM on August 26, 2006

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