Monday, April 16, 2012

Another 17,000,000 Years on the Coelacanth Timeline

"Skull Confirms Older Origin for 'Living Fossil' Fish"
Wynne Parry, LiveScience (April 10, 2012)

"A group of ancient fish, called coelacanths, have changed so little over time they are known as "living fossils." Now, the remains of a skull found in the Yunnan Province of China, confirms these creatures have been around, largely unchanged, for more than 400 million years.

"Once thought to have died out at roughly the time the dinosaurs disappeared, the first living coelacanth was discovered in a fishing net in 1938 off the eastern coast of South Africa. Since then, others have turned up elsewhere along the coasts of the Indian Ocean. [Image Gallery: Freaky Fish]

"While it's clear their history goes way back, the fossils they left behind have been scarce so far. A lower jawbone, more than 400 million years old and discovered in Australia, hinted at the earliest known emergence of coelacanths whose appearance matched the two species alive today. This small fossil has been described as the oldest coelacanth, but the authors of the recent research write that it offers so little information that it cannot be reliably placed within the fishes' family tree...."

Fascinating as they are, coelacanths are not particularly pretty fish. But, although some folks say they're an "endangered species," these critters were around before those dragonflies with two-and-a-half-foot wingspans flitted around. And they're still here.

(Alberto Fernandez Fernandez, via Wikipedia, used w/o permission)
"Preserved specimen of chalumnae (Also known as Coelacanth [1]) in the Natural History Museum, Vienna, Austria."

Ancient, and Apparently Durable

"...The discovery reinforces what was already suspected about coelacanths: After a period of rapid diversification long ago, these fish have remained pretty much the same over hundreds of millions of years, according to Matt Friedman, a lecturer in paleobiology at the University of Oxford, who was not involved in the research.

" 'It makes their sort of anatomical conservation, this lack of major change over geological time, much more impressive,' Friedman said.

"In fact, the discovery extends the record for coelacanths with modern-looking bodies back by about 17 million years, according to the researchers, led by Min Zhu of the Chinese Academy of Sciences...."

So far, coelacanths have survived assorted ice ages, asteroid impacts, and mobs of volcanoes that make the Mount St. Helens eruption look like a kitchen spill. Maybe they're not quite as delicate as they're supposed to be.

Pushing "coelacanths with modern-looking bodies back by about 17 million years" probably won't help American taxpayers who are struggling with tax forms while hoping that their request for an extension got processed. But the Lemming is fascinated by ugly fish that haven't changed much in 400,000,000 or so years.

Coelacanths, you see, are lobe-finned fish: which apparently led to tetrapods, critters with four limbs they use for moving around. Also lungfish, some of which 'walk' underwater, which suggests that walking started in the water.

Still awake?

The Lemming's noticed that peoples' eyes tend to glaze over pretty fast during these verbal meanders. And that's another topic.

Intermittent Ice Ages, Asteroid Impacts, and the Occasional Massive Volcanic Event

There may be planets where not much happens. Earth isn't one of them.

Some critters, like the koala, panda, and Bee Creek Cave Harvestman spider, require very special conditions. Change the environment, and they die.

Other critters, like rats, cockroaches, and - apparently - coelacanths, aren't quite as easy to kill off. Which is just as well, under the circumstances:
  • 225,000,000 years BP (before present)
    • Asteroid hits Earth
  • 200,000,000 years BP
    • Heavy volcanic activity starts
    • Pangea breaks in two
      • The gap got called "The Atlantic" recently
  • 199,400,000 years BP
    • Heavy volcanic ends
      • Elapsed time: 600,000 years
      • Crurotarsans are extinct
        • Leaving room for dinosaurs
  • 65,000,000 years BP
    • Asteroid hits Earth
      • Dinosaurs are extinct
      • Leaving room for mammals
        • And, eventually, humans
    (Adapted from March 24, 2010)
One of the critters that didn't make the cut, about a half-billion years back, was opabinia regalis: the thing shown in that sketch. It had five eyes, and isn't quite like anything that's alive today.

Recent Events: The Last 700,000,000 Years

The observable universe and been around for 13,730,000,000 years, give or take 120,000,000. That's a recent estimate by astronomers, cosmologists, astronomers, and physicists, anyway.

This timeline covers part of Earth's history, picking up the story around the time that glaciers reached the equator. By that time, single-celled critters (and maybe bigger) were leaving tiny (and rare) fossils.
  • -700,000,000 - 799,999,999 years BP
  • -600,000,000 - 699,999,999 years BP
  • -500,000,000 - 599,999,999 years BP
  • -400,000,000 - 499,999,999 years BP
    • -445,000,000: Lots of volcanoes; about 60% of marine invertebrates become extinct
    • -400,000,000 or so: Coelacanths show up
  • -300,000,000 - 399,999,999 years BP
  • -200,000,000 - 299,999,999 years BP
  • -100,000,000 - 199,999,999 years BP
    • -199,999,999 or so: lots of volcanoes for 600,000 years; Pangea cracks
    • Coelacanths still around
  • -0 - 99,999,999 years BP
  • Now
    • Coelacanths still around
These days, delicate critters teetering on the brink of extinction get a lot of attention. As important as that might be, the Lemming is also interested in why distinctly indelicate critters don't die out: and keep on not dying out. Sometimes for hundreds of millions of years.

Like coelacanths.

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