Features Thursday, October 23, 2014 - 05:30
The News Minute | October 20, 2014 | 2.25 pm IST Sexual intercourse was pioneered not by man but, by a group of long-extinct fish about 385 million years ago in Scotland, Australian scientists have reported. After studying the fossils of these ancient armoured fish called placoderms - which gave rise to all current vertebrates with jaws - the researchers found that their descendants switched sexual practices from internal to external fertilisation. "This was totally unexpected. Biologists thought that there could not be a reversion back from internal fertilisation to external fertilisation. We have shown it must have happened this way," said John Long, palaeontologist at the Flinders University in Adelaide, Australia. Male fish had bony, L-shaped genital limbs called claspers which transferred sperm into the female, a more effective way of reproduction compared to spawning in the water, News Now reported. The females, for their part, developed small, paired bones with which they locked the male organs in place in order to copulate. The researchers had previously shown that one placoderm species was the earliest animal known to have engaged in penetrative sex. But latest research reported by the journal Nature shows that an even earlier group of placoderms called antiarchs also used this method of fertilisation. "The finding is significant because antiarchs are considered the most basal (meaning those closest to the roots of the animal family tree) jawed vertebrates, and so it suggests that all placoderms reproduced through internal fertilization using claspers," Long added. But the implications of this finding are even more penetrating. According to Long, the oldest bony fishes which followed placoderms in the evolutionary tree show no evidence for internal fertilisation. "Thus, at some point, early fishes must have lost the internal fertilisation method seen in placoderms, before some of their descendants 're-invented' organs with a similar function - ranging from similar claspers in sharks and rays today to the penises of modern humans," the authors concluded. With IANS

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