* Astronomy

The abundant diversity of characteristics within species likely helped fuel the proliferation and evolution of an odd-looking creature that emerged from an unprecedented explosion of life on Earth more than 500 million years ago. University of Chicago palaeontologist Mark Webster reports this finding in the July 27 issue of the journal Science.

From an evolutionary perspective, the more variable a species is, the more raw material natural selection has to operate on - Mark Webster, an Assistant Professor in Geophysical Sciences at Chicago.

Palaeontologists for decades have suspected that highly variable species evolved more rapidly than others, said Nigel Hughes, Professor of Earth Sciences at the University of California, Riverside.

Various studies have approached questions pertaining to itbut this is the first to convincingly document it in any group - Nigel Hughes.

Most studies have focused on variability between species rather than within them, but in his Science paper, Webster analyzed 982 species of trilobites, ancient relatives of spiders and horseshoe crabs.

Theyre segmented little creatures, very beautiful to look at. They catch the eye of a lot of amateur collectors, and professionals like myself tend to get hooked on them very easily - Mark Webster.

Extinct for 250 million years, trilobites once were the most common creatures in the worlds oceans. Trilobites ranged in size from nearly microscopic to more than a foot long, though most of the 17,000 known species measured from one to four inches.

They were very diverse. That, in combination with their abundance as fossils, means theyre ripe for studying evolutionary patterns in very old rocks - Mark Webster.

Trilobites were among the creatures that emerged 500 million years ago, during what palaeontologists call the Cambrian explosion, or the Cambrian radiation. Before this time, life on Earth was limited mostly to bacteria, algae, single-celled organisms and only the simplest animal groups. But during the Cambrian Period, more complex creatures with skeletons, eyes and limbs emerged with amazing suddenness.

The paper is relevant to the big question of what fuelled the Cambrian radiation, and why that event was so singular - UC-Riversides Hughes of Websters study.

It appears that organisms displayed rampant within-species variation in the warm afterglow of the Cambrian explosion, Hughes said, but not later. No one has shown this convincingly before, and thats why this is so important.

Webster has hunted trilobites from the northwest highlands of Scotland to the deserts of the American Southwest. He specialises in the olenellids, the oldest, most primitive trilobite group ever to evolve. The olenellids also show a great deal of variation within species.

That led me into thinking theres something weird about these very primitive Cambrian trilobites that you dont see in other ones, he said.

The only way to verify his hunch was to conduct an analysis that combined the data compiled in previously published reports.

Its too much for one person to look at a thousand trilobite species - Mark Webster.

So for his Science study, Webster combed through 68 previously published studies of trilobites, searching for descriptions of evolving characteristics that could be incorporated into his analysis. After eliminating studies that were inappropriate for inclusion, 49 still remained.
He focused on actively evolving characteristics. The trilobite head alone, for example, displays many such characteristics. These include differences in ornamentation, number and placement of spines, and the shape of head segments. His findings: Overall, approximately 35 percent of the 982 trilobite species exhibited some variation in some aspect of their appearance that was evolving. But more than 70 percent of early and middle Cambrian species exhibited variation, while only 13 percent of later trilobite species did so.

Theres hardly any variation in the post-Cambrian. Even the presence or absence or the kind of ornamentation on the head shield varies within these Cambrian trilobites and doesnt vary in the post-Cambrian trilobites.

Palaeontologists have proposed two ideas to account for why variation within species declined through time. One is ecological. In the very early Cambrian seas, fewer organisms existed than today, which meant that they faced less competition for food.

You didnt really have to be tightly specialized to make a living in the Cambrian - Mark Webster.

But as evolution gave rise to more varieties of organisms, ecological communities became more diverse.

You had to be very fine-tuned to your particular niche to make a living and to beat out competitors for a limited resource.

The genomic hypothesis offers a second explanation for the decline of within-species variation over time. According to this idea, internal processes in the organism were the key factors. Various developmental processes interact with one another to control the growth and formation of body parts as any organism progresses from egg to adult.

Its been suggested that early on in evolutionary history, in the Cambrian Period, the degree to which these different developmental processes interacted with each other within the organism was a lot less. As a result, the constraints on what the final organism looked like were relatively low.

Both hypotheses are equally viable in light of Websters latest findings.

We need to tease apart whats controlling this pattern of high within-species variation. Theres a lot more work to do .

University of Chicago

One of the strangest mysteries of the fossil world concerns a tall, cylindrical structure dating to 420 million years ago. Some scientists have called it fungus, others a lichen, still others an alga. A new isotopic analysis has settled the debate, and has helped researchers hone their search for unknown life on other worlds.
Starting about 420 million years ago, a bizarre cylindrical life form called Prototaxites (pro-tow-TAX-i-tees) became a prominent element of the terrestrial landscape. Up to 8 metres tall, and as much as 1 meter in diameter, Prototaxites has confounded paloebotanists for nearly a century and a half.

Its large and strange, and people have debated what it was for very long time - C. Kevin Boyce of the University of Chicago, first author of a new paper on Prototaxites in Geology (May 2007).

Read more

An Oregon scientist and a Kentucky nurse have found the oldest known mushroom, entombed in a 100-million-year-old piece of amber from Burma.
A closer examination of the nine-hundredths-inch-long mushroom cap revealed that it had been infected by an ancient parasite, which a second parasite was feeding on.

"I was amazed enough with the mushroom. But then seeing the parasites was astonishing. No one has ever seen this three-tier association before" - George Poinar, a retired entomology professor in Corvallis.

Read more

New evidence that life existed on Earth as far back as 3.35 billion years has been found by a team led by a University of Western Ontario scientist.
The discovery -- fossilised tunnels made by microbes in Australia -- pushes the fossil evidence of life on the planet back to its early period.
Other evidence suggesting life on Earth existed about 500 million years earlier has been found, but that was chemical -- not fossil -- evidence, said UWO geologist Neil Banerjee.

"This is very strong evidence" - Neil Banerjee.

Read more