Video of the Day: The Largest Prehistoric Creature Ever to Roam Earth
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May 19, 2014

Video of the Day: The Largest Prehistoric Creature Ever to Roam Earth

 

      

 

John Hurt narrates the facts behind the discovery of huge nesting site in modern day Patagonia. Fossilised remains show Argentinosaurus laid tens of thousands of eggs in a 15 kilometer nesting site used for hundreds of thousands of years. The hatchlings, if they survive, will grow at an incredible rate. Over a 40 year life span Argentinosaurus can grow from 4 kg to 75 tons.

How did size of life on Earth spring from single-celled prganisms to Argentinosaurus to humans anf blue whales? "It happened primarily in two great leaps, and each time, the maximum size of life jumped up by a factor of about a million," Jonathan Payne, assistant professor of geological and environmental science at Stanford University. The world's scientific community has crunched the numbers on the animal kingdom’s sizes and shapes, and found that humans differ from each other far less than most species. The reason why is a mystery.

“We don’t have an answer. We have this interesting observation, but the explanation is an open hypothesis,” said evolutionary biologist Andrew Hendry of McGill University. In 2009, Hendry and Queens University biologist Ann McKellar combed through the scientific literature on body size and length in more than 200 species, from insects to fish to birds and, of course, humans.

They asked how humans compare to other animals in terms of body size variation. The team quantitatively compare levels of variation in body length (height) and mass within and among 99 human populations and 848 animal populations (210 species) and found that humans show low levels of within-population body height variation in comparison to body length variation in other animals. The further theorized that humans have evolved on a rugged adaptive landscape with strong selection for optimum body height variations that differ among locations.

All life on Earth all sprang from the same single-celled organisms that first populated the planet, so how did life grow in size from bacteria to homo sapiens to the blue whale?

Payne, along with a dozen other paleontologists and ecologists at 10 different research institutions, pooled their existing databases, combed the scientific literature and consulted with taxonomic experts in a quest to determine the maximum size of life over all of geological time. In addition to quantifying the enormity of the two leaps in maximum size, the researchers also pinned down when those leaps took place.

Both leaps coincided with periods when there was a major increase in the amount of oxygen in the atmosphere.

The first fossilized bacterial cells date to approximately 3.4 billion years ago, although life likely originated several hundred million years before. Between 2.7 and 2.4 billion years ago, cyanobacteria, formerly known as blue-green algae, originated and were of particular evolutionary and geological importance because they excrete oxygen as a waste product during photosynthesis. So far as science can tell, they were the first and only organisms to evolve oxygen-producing photosynthesis.

"All of the oxygen in the atmosphere ultimately exists because of the evolution of cyanobacteria," Payne said. "Plants that produce oxygen today during photosynthesis, their ability to do that is ultimately derived from cyanobacteria."

Single-celled bacteria remained the largest life form on Earth, cranking out the oxygen, until about 1.6 billion years ago. At that point, a new life form shows up in the fossil record.

"The first jump in maximum size happens when the first eukaryotic organisms show up as fossils," Payne said. "And those fossils are approximately a million times bigger than anything that had come before on Earth."

Although the first fossil eukaryotes were likely also single-celled organisms, the eukaryotes distinguish themselves by means of their internal structure and functioning. Instead of having the cellular processes of life take place by means of diffusion in the cell, eukaryotes have organized innards, with a nucleus and other cellular structures that are dedicated to specific functions in the respiratory process.

"The fossil record indicates pretty clearly that you need a eukaryotic cell to make that first size jump," Payne said. "It isn't just that the bacteria don't get there as fast, it is that bacteria still haven't gotten there 1.6 billion years later.

"Clearly, organismal organization matters," Payne said. "Not just at the time the size increase happens, but it continues to be a limitation on size.

For approximately the next billion years, life on Earth stayed about the same size, with only modest increases. Then about 600 million years ago, at the same time as another major boost in the amount of oxygen in the atmosphere, life leaped in size again.

This time, it was a million-fold size leap of multi-cellularity. Payne said there are clearly multi-cellular eukaryotes in the fossil record for several million years before this size leap, but the real explosion of size increase didn't happen until the oxygen level bumped up.

So why do the size leaps seem to hinge on the amount of oxygen in the air?

"There are a few things that could be going on," Payne said. "The first thing is that eukaryotic cells require oxygen for metabolism. So if they want to take organic matter and burn it up to have energy in their cell, they need oxygen. That sets the first and probably most important limitation."

Payne said this limitation also applies to multi-cellular eukaryotes, which likewise depend on extracting oxygen from the surrounding environment and using that in their cells to obtain energy. "There is also evidence that oxygen may mediate some other biochemical processes," he said.

As for just what triggered both the boosts in atmospheric oxygen, Payne said that isn't quite as clear. It may be that the first jump in oxygen came because cyanobacteria simply proliferated to the point that they were cranking out more oxygen than could be consumed through chemical reactions with material at Earth's surface, the only way that oxygen wouldn't have been released back into the atmosphere in the era before oxygen breathing creatures existed.

The possible causes of the second jump in oxygen are less clear, Payne said, but regardless of the puzzles that remain to be sorted out, the timing and magnitude of the jumps up in maximum size are clear. And Payne said the size jumps applied to a vast number of species.

"Whatever is controlling this second size increase appears to operate across many different groups. It is not something limiting one group alone," he said. "There also appears to be an increase even in the maximum size of groups of organisms like multi-cellular algae, so the size increase doesn't appear to be limited just to animals."

One other question remains to be answered: Can we look forward to another great leap in size? "We've speculated on that a little bit, just sort of thinking about what if you went up another step," Payne said.

"The next level of organization, going along this kind of theme, presumably would be something like insect societies, where you have individual multicellular eukaryotes that specialize in terms of what kind of function they carry out in a larger organization of these individuals. Something like an ant colony or a human society would be in some ways the next organizational level.

"But, if you look at human society as an example, we use so much of the gross primary productivity on Earth, it doesn't appear there would be room for a lot of species at that next level of organization and maximum size. At that point you're actually getting towards the physical size limits just imposed by the size of our planet."


The Daily Galaxy via www.mcgill.ca and stanford.edu

Comments

‘The world's scientific community has crunched the numbers on the animal kingdom’s sizes and shapes, and found that humans differ from each other far less than most species. The reason why is a mystery.’
Using natural selection as a base line, size, for humans, was not an important trait as it was for sauropods. The human species survived because of brain development. Brain development requires a significant investment in energy, so differences in body size became secondary, except in low calorie environments where diminished size is important.
Just a thought.

I honestly dont understand what the article was trying to say in the first paragraph comparing different animals (either by the superorder, family, genus or subspecies level) but i guess what i can get out of it is that dont expect major size differences on one species in a miniscule amount of time, but only modest size diff. corralated with envirnment, like say the leopard (Panthera pradus) subspecies, to an entire archosaur superorder known as the Sauropoda, u just can't really make the comparison, if i can remotely get the jist of what those 2 paragraphs where, i think trying to say. sauropods differed in so many sizes, oviously, the superorder existed to the entire jurassic, rite to the end of the cretaceous, and they were many families, too, so yea....

As for the argentinosaurus, being the biggest land animal EVER..... WWWWWWWRRRRRRRROOOOOONNNNNNGGGGGGGGGGGGGGGGG! i can't believe, in this day and AGE, this type of ignorance is going completely unchecked... sigh, i expected better from the Daily Galaxy, it makes me sad :-(... c'mon, serio, well i have to do justice on that matter. Have they not heard of Amphicoelias? (i simple vertification wouldn't kill them) I can't believe my eyes of the extreme ignorance when it comes to hard-in'd paleo information, that i know magnitudes more than the researchers mentioned here..

Amphicoelias is totally valid - in the sense of it being a valid genus with valid type material. However the type material (Amphicoelias altus) is from an animal no bigger than Diplodocus.

Amphicoelias fragillimus, the near-mythical giant vertebra that got lost, was only about 40% of the vertebra (if the published drawing can be believed) but based on that a 2m+ tall reconstruction has been drawn for the full bone by both Cope and Ken Carpenter.

For being a bone that no longer exists, it's definitely extremely popular. But the fact is, this isn't the biggest dinosaur we have currently existing fossil proof for. If more bones are ever found, it may actually need its own genus separate from Amphicoelias, the proportions are a bit different from A. altus, but not enough to definitively erect a new genus. The problem with this animal is not so much its validity (the bone is no longer around to analyze) but the fact that it's so poorly documentes (a single paper from Cope, and it isn't even the main focus of the paper). Cope could have made a scaling error, or a typo. The discovery was so obscure that for nearly a century nobody paid it any attention in major paleo-journals. So the real issue is that it wasn't really a big deal until the 1990s (and until the 1980s even PhDs thought there was nothing bigger than Brachiosaurus, despite larger and more massive sauropods (some still as yet undescribed) being known from Argentina since the 1920s (and possibly even since the late 1800s).

That said, there are some footprints scattered around the planet that could have been made by an A. fragillimus-sized creature. None of them are in the Morrison, but that doesn't rule out their discovery. But when you scale off of footprints, you really run into some serious problems. Unless you can scale a bigger animal from the same family off of bones, I'd avoid scaling from footprints, just don't do it! There's too much margin of error either way, either from splaying of the heel pads, or conversely from prints with caved-in edges that are too eroded to tell if they caved in. (for Breviparopus, I kept in mind that "Brachiosaurus" nougaredi can actually be scaled to a larger size based on a pretty huge partial sacrum, so Breviparopus is not a record-breaker even in Brachiosauridae - or even if you put it in another family.)


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