Friday, February 27, 2009

Prehistoric fish fossil find in Australia

Fish fossil points to origin of sex.

Yes, study of the 365 million-year-old prehistoric placoderm fish fossil from western Australia provides enough clues to the origin of sex. A pregnant fish fossil, the placoderm armor-plated variety that vanished from earth long back had a five-centimeter-long embryo. This embryo was earlier believed to be the remains of a meal by London's Natural History Museum, but now it is reported to be tiny bones of a young fish from two adult species of arthrodires (Incisoscutum ritchiei) in the womb of its mother. This finding now leads the scientists to believe that this fish might have reproduced by internal fertilization as against the earlier belief among the scientists that this placoderm created babies by mixing sperm and eggs in water. Reproduction, internal fertilization and live births had occurred often and earlier than previously thought. The pelvic fins of the fish had large claspers, which are intermittent erectile organs to assist the male to grip the female during mating. In most vertebrates including humans, the pelvic girdle supports the hind legs, but in fish it supports the pelvic fin, which helps stabilize them in the water. Placoderms are among the most primitive jawed vertebrates; they became extinct by the end of the Devonian or the “The Age of Fish” succeeded in evolution by the tetrapods.
Another live birth of a placoderm fossil from the Gogo formation of western Australia was reported last year.

Source: BBC News

Image: BBC News

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