Saturday, March 19, 2011

Fossil sex

Time for some fossils - and there is some interesting news to report! Oozing sap preserved 2 mites in the act of having sex 40 million years ago (1st image). The Baltic amber fossil has been analyzed by Pavel Klimov of the University of Michigan and Ekaterina Sidorchuk of the Russian Academy of Sciences. Their study shows that while today's male mites dominate the act of mating, the females of their extinct ancestors Glaesacarus rhombeus had the upper hand, so to speak. What they had, actually, was a special pad-like structure used to hold the male in place (and what he lacked was the clinging structure he now uses to keep the female in position). This gave the girl mites an evolutionary advantage by being able to choose superior males for mating partners and to avoid harassment by "losers."

Last month, analysis of a 160-million-year-old pterosaur fossil by Junchang Lü of Beijing's Institute of Geology and David Unwin of the University of Leicester revealed some new difference between the sexes of the Darwinopterus. The new Chinese fossil (4th image) shows a female pterosaur that suffered a broken wing and fell into a lake, where it was preserved beneath the sediments after gases caused by its decomposition expelled an egg. This allowed the scientists to determine that the small flying reptiles laid leathery eggs like turtles rather than hard-shelled eggs like birds. In addition - because they are certain this fossil is female - they can state that only the males sported large head crests, making them the "peacocks of the Mesozoic."

In an earlier post about frisky fossils, I noted that in 2010 paleontologists had identified fish as the first creatures to engage in sex for pleasure. Well, back in 2008 they determined that Funisia dorothea (2nd image), tube-like organisms that lived on the sea floor in flocks 570 million years ago, were the first to engage in the act at all, rather than reproducing asexually like everything else. "I don't think they would wind around each other. But I could be wrong - I would like to think they enjoyed it," said researcher Mary Droser of the University of California Riverside.

Just days after the mating mites made headlines, University of Cincinnati geology professor Carlton E. Brett revealed his assessment of large trilobite gatherings, preserved often in the fossil record (example, 3rd image), as opportunities for molting and mating. As he put it, "It's an orgy."

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