Better Article:


Fins to Limbs: New Fossil Gives Evolution Insight

John Roach
for National Geographic News
April 1, 2004


Today researchers announced their discovery of a 365-million-year-old fossil limb bone of an ancient tetrapod. Tetrapods, including humans, are four-limbed animals with backbones. The fossil was found during road construction that revealed an ancient streambed.
See an illustration of the animal and a fin-to-limb evolution chart.

Scientists say the find will help shed light on how early animals evolved limbs from fins. This crucial adaptation enabled Earth's animal life to crawl from water to land.


A 365-million-year-old fossil limb bone of an ancient tetrapod will help shed light on how ancient animals evolved limbs from fins, researchers announced today. Tetrapods are four-limbed animals with backbones.

The bone—a humerus, or upper arm or forelimb—is one of the earliest tetrapod limb bones ever found. (Tetrapods today include amphibians, mammals, reptiles, and birds, among others.)

The ancient bone shares features with primitive fish fins, but also has characteristics of a true limb bone. It bridges the gap between fish and amphibian.

"The transition wasn't all or nothing," said Ted Daeschler, a vertebrate zoologist with the Academy of Natural Sciences in Philadelphia "It's not that some animals were thrown on land. There were certainly other functions intermediate."

Daeschler and colleagues Neil Shubin and Michael Coates, paleontologists at the University of Chicago, say the fossil bone offers a window onto this intermediate stage.

The National Geographic Society Committee for Research and Exploration and the National Science Foundation supported the scientists' research. The trio describe the fossil in tomorrow's issue of the journal Science.

From Stream to Shore

"This new humerus shows some primitive features that are lost in later tetrapods but in this specimen have already begun to change their orientation into tetrapod-like configuration," said Jennifer Clack, a paleontologist at the University Museum of Zoology Cambridge, United Kingdom.

Clack, an expert on the fish-tetrapod transition, also wrote an essay on the discovery for Science.

To understand how tetrapods evolved limbs from fins, Shubin said it helps to imagine the environment that these creatures lived in. "Think of a shallow stream choked with plants, not of an open sea," he said. "At some level, these shallow streams approach a more terrestrial environment in the ways that animals would move around."

According to Daeschler, such an environment would require fish to have limblike fins to propel themselves along the surface of shallow waters, hold their position in a current, or lift their head to the water's surface to gulp air.

Push-Ups

The humerus—which the scientists say clearly belongs to a limbed amphibian and not a lobbed-fin fish—suggests that the tetrapod was an animal that had a powerful forelimb with a large area for the attachment of muscles at the shoulder. Such a muscle is associated with the ability to perform a push-up.

"The [newfound] humerus enables comparisons with fish that were not possible until now," Shubin said. "There is a large crest on the lower side of this humerus—it is where the pectoral muscle would attach. This same expanded crest is seen in fish."

The presence of a place to attach a pectoral muscle in both fish and tetrapods suggests that the ability to perform a push-up is ancient, evolving first in fish and not in terrestrial animals as was originally believed.

"The notion is that this movement is primitive," Shubin said. He believes the movement first arose in fish that required the appendages to move. That motion was akin to how creatures eventually used limbs to walk on land, Shubin said.

According to the researchers, however, fish with limblike fins had no intention of walking on land. Rather, they were adapting to their environment.

"When fish used their fins to prop themselves up on the bottom … it was a useful invention at that time" that helped fish "make a good living" feeding in their aquatic environment, Daeschler said.

Roadside Fossil Trove

The ancient tetrapod humerus is among several plant and animal fossils collected from an ancient streambed in north central Pennsylvania in 1993. Like many fossil sites in the region, the streambed was exposed as road crews cut through the bedrock in the course of constructing a highway.

"What we need are fresh exposures of bedrock. Pennsylvania has wonderful sequences of rock from this time period," Daeschler said. "But most of it is covered by forest or farmland."

So when road crews cut through bedrock, researchers make arrangements to study the fresh exposures. They often bring layers of rock back to their labs for painstaking analysis.

The research team has previously discovered fossil remains of two other tetrapods—Hynerpeton and Densignathus—from this same ancient streambed. But the significance of the new humerus went undetected for several years, since only a small portion of the bone was exposed.

In 2001 Fred Mullison, a staff scientist at the Academy of Natural Sciences in Philadelphia, excavated the bone from the rock. Only then did the fossil's import became apparent.

Daeschler and colleagues say they are unable to discern whether the humerus belongs to Hynerpeton, Densignathus, or an entirely new tetrapod species.

"We can't prove it's either or neither of them. So rather than throw another name on this thing … we're saying it is an early tetrapod humerus," Daeschler said.

The research team hopes further excavations will reveal more tetrapod fossils and provide more insights into a key evolutionary milestone—fins to limbs—of life on Earth.

http://news.nationalgeographic.com/...apodfossil.html

___________________
Retro ...

THE EARTH IS SIX THOUSAND YEARS OLD!

DARWINISM IS A THEORY! A THEORY!!!! EVOLUTION IS A THEORY. NOT A FACT!!!

"Evolution has not been proven," said Taylor, who joined the debate over what should be taught in Cobb schools after reading about the ACLU lawsuit. "There are a growing number of scientists who are skeptical about Darwinism."

God, Cobb County and most of the radicals are a bunch of retards, Creationism/"Intelligent Design" != Science










cool stuff occrider

quote:

Originally posted by occrider Better Article: Fins to Limbs: New Fossil Gives Evolution Insight John Roach for National Geographic News April 1, 2004[/url]

April Fools

Better start going to church

quote:

Originally posted by occrider Fins to Limbs: New Fossil Gives Evolution Insight John Roach for National Geographic News April 1, 2004

ahh you see, it's from 1st april, doesnt that say you anything

edit: ooooops, too slow answering there... hehe... good article btw =)

Oh Occ, Jesus didnt have fins! LOL




OMG|

___________________
'That's like telling a Kodiak bear to stop fcking older men.'

nice find occ

newscientist equivalent:

http://www.newscientist.com/news/news.jsp?id=ns99994843

it's interesting seeing the humerus equivalent of this animal in a fish and a human

here are two other recent articles on evolution if anyones interested:

http://www.newscientist.com/news/news.jsp?id=ns99994840
Rat genome reveals supercharged evolution

http://www.newscientist.com/news/news.jsp?id=ns99994786
No Moon, no life on Earth, suggests theory

More news from the evolution newsfront. Perhaps we should have a sticky for all the evolution news? It's only going to grow with time .

Penn State Study Finds Origins of Snakes

By DAN LEWERENZ
Associated Press Writer

STATE COLLEGE, Pa. (AP) -- Using DNA evidence, two Penn State University researchers think they have answered a long-standing question among scientists: Did snakes evolve from land-based lizards, or did they come from the sea?

In an article for the May 7 issue of the journal Biology Letters, Penn State biology professor Blair Hedges and postdoctoral scholar Nicolas Vidal write that the genetic evidence strongly suggests that snakes evolved from land-dwelling lizards.

It's a conclusion that confirms a general trend in evolutionary biology, but bucks more than 100 years of thinking about reptiles, Hedges said.

The first tetrapods, or four-legged creatures, migrated from the oceans onto land 365 million years ago. Many animals later returned to the sea, including the ancestors of modern dolphins and whales - their arms and legs evolved into fins.

Herpetologists, though, have been divided about the origin of snakes. Some thought snakes evolved from land-based lizards, losing their legs to better squeeze through small holes and crevasses close to the ground. Others thought aquatic lizards, such as mosasaurs, made a second migration onto land as snakes.




Evidence for the aquatic theory came largely from physical similarities between monitor lizards such as the Komodo dragon - the closest living relatives of mosasaurs - and snakes.

"Monitors have these long, forked tongues like snakes, and not many other lizards have similar tongue morphology," Hedges said. "The body shape of a monitor is very long and snakelike. The jaws are very large and tending toward the snake's jaw type. So there were several lines of evidence, morphologically, that point toward a snake-monitor relationship."

To test that theory, Vidal and Hedges compared the DNA from 17 of the 25 known families of snakes to DNA from all 19 families of lizards. They found snakes to be much more similar to land-based lizards than they were to monitors, providing strong evidence for a terrestrial evolution.

"In the last five or so years, people looking at gene sequences have claimed that they found support for a monitor-snake relationship in the sequence data," Hedges said. "But in all cases, they were missing many families of lizards, so I guess you could say the didn't have all the data to really say that for certain.

"When we had all of the families' data, it clearly showed there was no snake-monitor relationship."

Although the evidence contradicts the strongly held beliefs of some herpetologists, Nancy J. Berner, associate professor and chair of biology at the University of the South, said the DNA comparison would be strong evidence for those looking strictly at physical similarities.

"The thing that really caught my attention, and that I think is really significant, is that the investigators were looking at genetic relatedness as opposed to anatomical structures," Berner said. "What this does is it's taking the new technology that's out there and applying it to an old question, really testing old theories. I would say that they're really on to something here."

Although their research leads Hedges and Vidal away from the monitor lizards and the aquatic theory, they still haven't determined exactly where snakes began to separate from the lizard family tree.

"Now we need to identify the closest relative of snakes. We don't have it yet," Vidal said. "We can exclude monitors - that's statistically supported, strongly - so we know their origin is not marine. But all of the other lizard lineages are terrestrial, so we have to find which one."

http://customwire.ap.org/dynamic/st...EMPLATE=DEFAULT

___________________
Retro ...