La llaman "Explosión de Avalon"


Scientists have known for some time that most major groups of complex
animals appeared in the fossils record during the Cambrian Explosion, a
seemingly rapid evolutionary event that occurred 542 million years ago. Now
Virginia Tech paleontologists, using rigorous analytical methods, have
identified another explosive evolutionary event that occurred about 33
million years earlier among macroscopic life forms unrelated to the Cambrian
animals. They dubbed this earlier event the "Avalon Explosion."
The discovery, reported in the January 4 issue of Science, suggests that
more than one explosive evolutionary event may have taken place during the
early evolution of animals.

The Cambrian explosion event refers to the sudden appearance of most animal
groups in a geologically short time period between 542 and 520 million years
ago, in the early Cambrian Period. Although there were not as many animal
species as in modern oceans, most (if not all) living animal groups were
represented in the Cambrian oceans. "The explosive evolutionary pattern was
a concern to Charles Darwin, because he expected that evolution happens at a
slow and constant pace," said Shuhai Xiao, associate professor of geobiology
at Virginia Tech. "Darwin's perception could be represented by an inverted
cone with ever expanding morphological range, but the fossil record of the
Cambrian Explosion and since is better represented by a cylinder with a
morphological radiation at the base and morphological constraint
afterwards."

Darwin reckoned that there should be long and hidden periods of animal
evolution before the Cambrian Explosion, Xiao said.

But paleontologists have not found such evidence, and recently scientists
have learned that biological evolution has not been moving on a smooth road.
"Accelerated rates may characterize the early evolution of many groups of
organisms," said Michal Kowalewski, professor of geobiology at Virginia
Tech.

To test whether other major branches of life also evolved in an abrupt and
explosive manner, Virginia Tech graduate students Bing Shen and Lin Dong,
along with Xiao and Kowalewski, analyzed the Ediacara fossils: the oldest
complex, multicellular organisms that had lived in oceans from 575 to 542
million years ago; that is, before the Cambrian Explosion of animals. "These
Ediacara organisms do not have an ancestor-descendant relationship with the
Cambrian animals, and most of them went extinct before the Cambrian
Explosion," said Shen. "And this group of organisms - most species - seems
to be distinct from the Cambrian animals."

But how did those Ediacara organisms first evolve, Shen asked. Did they also
appear in an explosive evolutionary event, or is the Cambrian Explosion a
truly unparalleled event"



http://www.fossilscience.com/Researc...lular_life.asp

En el circo evolucionista le están creciendo los enanos
tex.