Time to study....

[OutletPass]

Fossil Illuminates Evolution of Limbs from Fins

The discovery of a 365-million-year-old forelimb is helping scientists better understand how ancient creatures made the transition from water to land. A report published today in the journal Science describes the fossil, which represents an intermediate stage in the evolution of fish fins into vertebrate limbs.

Neil H. Shubin of the University of Chicago and his colleagues recovered the bone, which was encased in a brick-size piece of red sandstone, from the side of a highway in north central Pennsylvania. The layered rocks are the remains of a stream system dating back to the Late Devonian Period. "We knew it was a humerus," study co-author Michael I. Coates of the University of Chicago recalls, "but it was an entirely different kind. We had never seen one like it before." For example, compared with the anatomy of other tetrapods of the same age there is a large space for chest muscle attachment, the scientists report. This added brawn would have enabled a motion similar to a benchpress or push-up. Based on the apparent size and extent of the muscles, the authors posit that the humerus played a significant role in the support and movement of the animal.

The findings indicate that the ability to prop up the body is more ancient than previously believed. Says Coates, "This means that many of the features that we thought evolved to enable life on land originally evolved in fish living in aquatic ecosystems." Other fossils recovered from the same site indicate that the waterway was home to a variety of plant and animal life. The forelimb would have allowed the animal to propel itself along the bottom of the riverbed or elevate its head out of the water. In an accompanying commentary Jennifer A. Clack of the University of Cambridge notes that Devonian tetrapods "probably did not walk efficiently, but their modes of locomotion certainly varied, as they adapted skeletons and sensory organs for the challenges posed by emergence from the water." --Sarah Graham

[Caliente]

Cool post.

[kingrex]

Interesting, yet rather random post. [img]i/expressions/face-icon-small-smile.gif[/img]

What is the source for this study?

[OutletPass]

Kingrex...it was carried on the Associated press....from a Science magazine article that published a study done at the university of Chicago...

Here's the most recent story.

Fossil arm holds evolutionary secrets
Friday, April 2, 2004 Posted: 11:07 AM EST (1607 GMT)

The fossil of an arm bone with characteristics of both a fish and a tetrapod as it appears on the cover of Science.


WASHINGTON (AP) -- A 365-million-year-old arm bone fossil found in Pennsylvania came from one of the first creatures able to do push-ups, an evolutionary step that was necessary for animals to move from the sea to dry land. When the animal lived, there were no vertebrates on dry land, and the oceans were a place of fierce, toothy meat eaters living a predatory life of eat or be eaten.

It was into this hostile environment that a two-foot-long animal that was more than a fish and less than a true amphibian made its brief appearance in the fossil record, said researcher Neil Shubin. The four-legged creature had a humerus, or upper arm bone. Such a bone, far different from the flipper bones of fish, gave the creature an important new ability -- it could raise its upper body like an athlete doing push-ups.

"This animal was there for just a brief moment in time," said Shubin, a paleontologist at the University of Chicago. "It was only later that we start seeing in the fossil record things that commonly walked on land." The animal's upper arm bone shows that evolution was already preparing vertebrates for their grand invasion of the world beyond the beach and the eventual appearance on land of amphibians, reptiles, dinosaurs, birds and mammals.

"It could have evolved this for a variety of reasons, including pushing its head up out of the water to breathe or to walk around in shallow water," Shubin said. "And we can't exclude the possibility that it walked on land." He said other similar tetrapods from around the same period are known to have had both gills and lungs and, thus, could breathe either under or above the water. The animal's arm bone fossil has a bony crest that formed the anchor for powerful chest, or pectoral, muscles.

"That is the muscle used when you do a push-up or a bench press," said Shubin. "And that is the muscle that is super-emphasized in this animal." Paleontologist Ted Daeschler holds the 365-million-year-old fossil of an arm bone in his office at The Academy of Natural Sciences in Philadelphia on Wednesday. He said the shoulder joint was primitive, rather like a hinge that could move the arm up and down. The human shoulder joint enables the arm to swivel and twist and turn through many degrees of motion in several directions.

"These animals had a hinge in the shoulder that allowed them to do just one thing -- push-ups," said Shubin. "That was a stage that our common ancestors went through before evolution eventually developed the classic ball-and-socket joint," as in human shoulders. Jennifer A. Clack, a researcher at the University of Cambridge in England, said the discovery by Shubin and his co-authors suggests the humerus bone could have come from a previously unknown tetrapod that needed its limbs to bear weight, as required when living on land.

Discovery of the new fossil, she said, should stimulate a closer analysis of fossils from the Pennsylvania site where the new discovery was made. The tetrapod fossil was discovered in a road cut in a part of western Pennsylvania. The road construction revealed layers of rock that were laid down as sediment when the area was covered by a vast inland sea, stretching from what is now the Gulf of Mexico deep into the heartland of North America.

Shubin said the animal, which has not been named, lived in a river delta, an area where water draining from mountains to the east joined the inland sea.Other fossils indicate that almost all of the other animals living in the area were meat-eating fish, some 15 feet (3.5 meters) long with teeth the size of railroad spikes. One of those predators may have killed the tetrapod whose fossil Shubin and his co-authors studied. He said the bone bears faint marks of what might have been tooth marks.

"It was highly hostile and predatory, so there were lots of things that could have eaten this guy," said Shubin.

Copyright 2004 The Associated Press. All rights reserved.This material may not be published, broadcast, rewritten, or redistributed.

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How the rest of us evolved