Tuesday, October 12, 2010

Fossil fish fooled around

My stepfather Del (pictured below after filleting the 30lb black drum he caught this summer) spotted this fish story in the weird news yesterday. Fossils of Late Devonian ptyctodontid and arthrodiran placoderm fishes discovered in Western Australia suggest that these fish, which were similar to modern sharks, were the 1st animals to have sex for pleasure. This achievement, rather than merely spawning, occurred in the early Devonian Period (400 to 410 million years ago) theorizes John Long of the L.A. County Natural History Museum and his colleagues: "Our finds show that these extinct armored fishes, the placoderms, had intimate copulation with males inserting claspers (a structure that is part of the pelvic fin) inside the female to deposit sperm."

Just 2 years ago, Long - then at Museum Victoria in Melbourne - announced another extraordinary discovery from the same fossil formation. He found a 10" female placoderm with an embryo and umbilical cord inside her body. "I think this is one of the most extraordinary fossil finds of all time, as it is the first time in history we have a maternal feeding structure preserved in any fossil. When I first saw the embryo inside the mother fish my jaw dropped, I was silent, stunned like a mullet. I realised that in my hands was the oldest known vertebrate embryo," said Long. It was the earliest evidence of an animal giving live birth, and pushed the known record of such reproduction back by some 200 million years. An embryo inside its mother indicates that placoderms must have copulated to produce offspring, instead of laying eggs and fertilizing them outside the mother's body.

After the discovery of the embryonic fish, other museums reexamined their placoderm fossils to assess whether smaller fish found inside their bodies were food they had eaten or young they were gestating. I have trouble visualizing all of this from the fossil, which is why I appreciated the artists' renditions above.

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