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Study shows primitive fish had genetic wiring for limbs

Primitive FishPrimitive fish already may have possessed the genetic wiring needed to grow hands and feet well before the appearance of the first animals with limbs roughly 365 million years ago, scientists said on Wednesday.

University of Chicago researchers were seeking clues behind a momentous milestone in the evolution of life on Earth -- when four-legged amphibians that descended from fish first colonized dry land. These first amphibians paved the way for reptiles, birds and mammals, including people.

They studied one of the most primitive types of fish on Earth -- the long-snouted paddlefish Polyodon spathula -- and found the fish that predated the first land vertebrates may have possessed genetic underpinnings for limb development.

Paddlefish, found in freshwater locales in the United States and China, are early "ray-finned" fish. Their fleshy fins are structurally similar to fish predating the first land creatures. Their fins contain cartilage thought to correspond to the upper arm bone of land vertebrates.

While paddlefish are ancient, they did not exist at the time of the vertebrate conquest of land, but are seen as an evolutionary offshoot of some fish around at that time.

Shubin and other scientists last year announced the discovery of the remains of a creature called Tiktaalik dating back to 375 million years ago and seen as a missing evolutionary link between fish and the first land vertebrates.

It had fish-like characteristics, but it boasted a skull, neck, ribs and parts of limbs resembling the first amphibians such as Acanthostega that arose 5 to 10 million years later.

"So it seems like you had the genetic tool kit (for limbs) for a long period of time," Shubin said. "And then, when the new ecosystems appear at around the time of Tiktaalik and slightly before, that's when forms started to use that to make true fingers and toes and stuff like that."

Link & Image: Yahoo News
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