This site is not maintained. Click here for the new website of Richard Dawkins.

Single-Celled Giant Upends Early Evolution

Thanks to BanJoIvie for the link.

Reposted from:
http://dsc.discovery.com/news/2008/11/20/gromia-cambrian.html

cellNov. 20, 2008 -- Slowly rolling across the ocean floor, a humble single-celled creature is poised to revolutionize our understanding of how complex life evolved on Earth.

A distant relative of microscopic amoebas, the grape-sized Gromia sphaerica was discovered once before, lying motionless at the bottom of the Arabian Sea. But when Mikhail Matz of the University of Texas at Austin and a group of researchers stumbled across a group of G. sphaerica off the coast of the Bahamas, the creatures were leaving trails behind them up to 50 centimeters (20 inches) long in the mud.

The trouble is, single-celled critters aren't supposed to be able to leave trails. The oldest fossils of animal trails, called 'trace fossils', date to around 580 million years ago, and paleontologists always figured they must have been made by multicellular animals with complex, symmetrical bodies.

But G. sphaerica's traces are the spitting image of the old, Precambrian fossils; two small ridges line the outside of the trail, and one thin bump runs down the middle.
At up to three centimeters (1.2 inches) in diameter, they're also enormous compared to most of their microscopic cousins.

"If these guys were alive 600 million years ago, and their traces got fossilized, a paleontologist who had never seen this thing would not have a shade of doubt attributing this kind of trace to the activity of a big, multicellular, bilaterally symmetrical animal," Matz said.

"This is a very important discovery," Shuhai Xiao of Virginia Polytechnic Institute said. "The fact that protists can make traces has important implications for how we interpret many trace fossils."

The finding could overturn conventional thinking on a mysterious time in the evolution of early life known as the Cambrian Explosion. Until about 550 million years ago, there were very few animals leaving trails behind. Then, within ten million years an unprecedented blossoming of life swarmed across the planet, filling every niche with hard-bodied, complex creatures.

"It wasn't a gradual development of complexity," Matz said. "Instead these things suddenly seemed to burst out of a magic box."

Charles Darwin first noticed the Cambrian Explosion and thought it was an artifact of a poorly preserved fossil record. The precambrian trace fossils were left by multicellular animals, he reasoned, so there must be some gap in fossils between the nearly empty Precambrian and the teeming world that quickly followed. But if the first traces were instead made by G. sphaerica, it would mean the Explosion was real; it must have been a diversification of life on a scale never before seen.

Genetic analysis of the water-filled G. sphaerica cells also reveals tantalizing clues that it could be the oldest living fossil on the planet.

"There's a 1.8 billion-year-old fossil in the Stirling formation in Australia that looks just like one of their traces, and with a discoidal body impression similar to these guys." Matz said. "We haven't proved anything, but we might be looking at the ultimate living macroscopic fossil."

TAGGED: BIOLOGY, EVOLUTION, PALEONTOLOGY


RELATED CONTENT

Planet of the apes

Stephen Cave - Financial Times Comments

What we really know about our evolutionary past – and what we don’t

WALK DARWIN’S TREE OF LIFE ~ 25 - 26...

- - Ancestors Trail Walk Comments

WALK DARWIN’S TREE OF LIFE ~ 26 AUGUST 2012 - event begins on Saturday 25 August

Astrophysicists simulate 14 billion...

Liat Clark - Wired.co.uk Comments

Astrophysicists simulate 14 billion years of cosmic evolution in high resolution

Study casts doubt on human-Neanderthal...

Alok Jha - The Guardian Comments

Cambridge scientists claim DNA overlap between Neanderthals and modern humans is a remnant of a common ancestor

Why do organisms build tissues they...

- - Science Blog Comments

Why, after millions of years of evolution, do organisms build structures that seemingly serve no purpose?

New flat-faced human species possibly...

Charles Choi - CBS News Comments

Four decades ago, in 1972, the Koobi Fora Research Project discovered the enigmatic fossilized skull known as KNM-ER 1470 which ignited a now long-standing debate about how many different species of early Homos existed.

MORE

MORE BY DISCOVERY

MORE

Comments

Comment RSS Feed

Please sign in or register to comment