Mass Extinctions: 'Giant' Fossils Are Revolutionizing Current Thinking

ScienceDaily ^ | February 11, 2010 | Adapted from materials provided by CNRS

[SunkenCiv]

Large-sized gastropods (up to 7 cm) dating from only 1 million years after the greatest mass extinction of all time, the Permian-Triassic extinction, have been discovered by an international team including a French researcher from the Laboratoire Biogéosciences (CNRS/Université de Bourgogne), working with German, American and Swiss colleagues. These specimens call into question the existence of a "Lilliput effect," the reduction in the size of organisms inhabiting postcrisis biota, normally spanning several million years. The team's results... have drastically changed paleontologists' current thinking regarding evolutionary dynamics and the way the biosphere functions in the aftermath of a mass extinction event... Over the last 540 million years, around twenty mass extinctions, of greater or lesser intensity, have succeeded one another. The most devastating of these, the Permian-Triassic (P-T) mass extinction, which decimated more than 90% of the marine species existing at the time, occurred 252.6 million years ago with a violence that is still unequaled today.

In the aftermath of such events, environmental conditions are severely disrupted: the oceans become less oxygenated, water becomes poisonous, there is increased competition, collapse of food chains, etc. Until now, it has generally been accepted that certain marine organisms, such as gastropods or bivalves, were affected by a drastic reduction in size in response to major disruptions of this nature, both during and after the event. It took several million years for such organisms to return to sizes comparable to those that existed prior to the crisis. This is what scientists call the "Lilliput effect," in reference to the travels of Gulliver who was shipwrecked on the island of the same name, inhabited by very small Lilliputians.

[SunkenCiv]

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[BereanBrain]

my favorite pet theory about the predominance of gigantism in fossils is that the earth had much higher barometric pressure in the distant past. Higher pressure allows cells to grow larger since they can be oxygenated better.

So aminals had the same DNA, same number of cells, just each cell was larger.

This changed after earth’s pressure was reduced by meteor strike and/or global flood calamity.

[verity]

What would account for the giant anal orifices permeating the Obama administration? lol

[r9etb]

While the story was interesting, I confess that I was more interested by the little box at the bottom, offering a choice of citation formats.... My kids are to the point now where they’re writing papers that require references, and the article offered a couple of alternatives (APA and MLS). Pretty nifty little gadget!

[Hegemony Cricket]

Huge midgets.

[EnderWiggins]

The problem with that theory is that the largest living organisms that have ever been discovered are still alive today; Blue whales.

So apparently, higher barometric pressure is not necessary for large size.

[Nachum]

Huh. They all died at one time. Interesting. Like- there could have been a great big flood....

[yefragetuwrabrumuy]

A lot of the unknowns can be explained with two phenomena. The first is the unequal distribution of fossils. That is, fossilization is very rare, and only takes place in very limited conditions around the world. If these places become uninhabited, it seems like lots of species have disappeared. But in truth, it just means a gap until they next occupy a place where fossilization occurs.

The other phenomena is the flip side of this, called “the Lazarus effect”, where most of a species is killed off, leaving only a few small colonies behind, taking them a great length of time to repopulate regions in which they used to live.

Between the two, it is not surprising to imagine strange extinction and recovery events. We live in a very volatile world.

[SunkenCiv]

thanks bb.

[TexGuy]

Huge midgets.

$9.99 a pound under the name "Jumbo Shrimp" ...

[Fred Nerks]

Ammonite fossil.

[null and void]

The theory isn’t completely dead, It could still apply to critters without a decent circulatory system and set of lungs/gills.

Dragonflies with 3 foot wingspans come to mind.

(Side question, how much atmosphere did the Chicxulub impact blast into space?)

[EnderWiggins]

"The theory isn’t completely dead, It could still apply to critters without a decent circulatory system and set of lungs/gills.

Dragonflies with 3 foot wingspans come to mind.

A 30 inch wingspan is not the key measure. The body of the Meganeura "dragonfly" was only 18 inches long. There are walking sticks that are 13 inches long that are living today. So... yeah they were big, but not uniquely so.

The real problem though is that gigantism doesn't actually associate with specific time frames. Different organisms or types of organisms express gigantism at different times. They don't provide a pattern of generally larger to smaller over time, or as the result of a certain event where suddenly organisms generally became smaller.

Certainly, the fossil record tends to preserve larger organisms preferentially over smaller... and we also tend to emphasize in our media the extremes over the ordinary. Giant dragonflies and cockroaches of the Carboniferous get our attention... but the simple truth is that most dragonflies and cockroaches of the Carboniferous were little bitty guys, just like today.

As to your aside... it is not clear to me that the K-T event would have blasted any atmosphere into space. I certainly cannot find any references or models that would indicate it did. (Side question, how much atmosphere did the Chicxulub impact blast into space?)

[SunkenCiv]

That’s a lot of escargot. ;’)

[Ernest_at_the_Beach]

Was that found in Australia?

[wbill]

“The world’s smallest large-screen television”.

[wolfcreek]

We have these and Large-sized gastropods (up to 7 cm) (some bigger) in our backyard here in central Texas. (elevation about 990 ft.)

[Fred Nerks]

AMMONITE FOSSILS. LINK

sorry, I saved the image but not the source, and the above website that features the same ammonite doesn't say. Here's a nice one: