BEIJING, Aug. 2 (Xinhuanet) -- A 400 million-year-old
fossilized coelacanth fin is providing insight into how fins evolved into limbs
for walking on land because the arrangement of bones within the fin match the
patterns found in living ray-finned fishes, not present-day coelacanths.
Scientists found the 4-inch-long (10-centimeter-long)
specimen at Beartooth Butte in northern Wyoming and have named the fish
Shoshinia arctopteryx after the Shoshine people and the Shoshone National
Forest. When alive, the fish would have been about 18 to 24 inches (46 to 62
centimeters) in length
Until now, scientists had assumed the living
coelacanths and their relatives, the lungfish, served as accurate models of
their ancestors dating back hundreds of millions of years ago.
"Two living fossils, coelacanths and lungfishes, are
in fact not primitive," said lead author Matt Friedman of the University of
Chicago. "They are specialized, and they are not particularly good models for
understanding the origin of limbs."
Actually, living coelacanths are adapted for
deep-water environments off the coasts of India and Africa where they use a
specialized organ in their nose to detect weak electrical signals from prey
buried in the mud along the seafloor.
Unlike fins on living coelacanths and lungfishes, the
fossil fin has an asymmetrical pattern in which there are more bones on the
front of the central shaft than the back. It has more in common with the anatomy
of four-limbed vertebrates, called tetrapods, and even humans than it does with
the anatomy of living coelacanths.
The discovery of the new fossil means scientists can
no longer make inferences about the evolution of limbs based on living
coelacanths and lungfishes.
"To understand the developmental evolution of the
limbs of tetrapods, we shouldn't be looking at the fins of our nearest living
fish relatives ¡ª lungfishes and coelacanths ¡ª because they're far too
specialized," said co-author Michael Coates, a University of Chicago
biologist.
(Agencies)
