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 In an important discovery in the evolutionary history of sexual
reproduction, the scientists found that male fossils of the
Microbrachius dicki, which belong to a placoderm group, developed
bony L-shaped genital limbs called claspers to transfer sperm to
females.
Females, for their part, developed small paired bones to lock the
male organs in place for mating.
Placoderms are the earliest vertebrate ancestors of humans.
"Placoderms were once thought to be a dead-end group with no live
relatives, but recent studies show that our own evolution is deeply
rooted in placoderms and that many of the features we have -- such
as jaws, teeth and paired limbs -- first originated with this group
of fishes," said John Long, a paleontologist at Flinders University
in South Australia who led the research.
This new finding, he added, shows that "they gave us the intimate
act of sexual intercourse as well".
Matt Friedman, a paleobiologist from Britain's Oxford University who
was not involved in the research, described its findings as "nothing
short of remarkable" and said they suggested much more could be
learned from the fossil fishes.
Long, whose study was published in the journal Nature on Sunday,
discovered the ancient fishes' mating abilities when he stumbled
across a single fossil bone in the collections of the University of
Technology in Tallinn, Estonia, last year.
The research then involved scientists from Australia, Estonia,
Britain, Sweden and China, who analyzed fossil specimens from museum
collections across the world.
These demonstrate the first use of internal fertilization and
copulation as a reproductive strategy known in the fossil record.
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Measuring about 8 centimeters (3 inches) in length, Microbrachius
lived in ancient lake habitats in Scotland, as well as parts of
Estonia and China.
Long explained that "Microbrachius" means little arms, but said
scientists have been baffled for centuries by what these bony paired
arms were actually there for.
"We've solved this great mystery," he said. "They were there for
mating, so that the male could position his claspers into the female
genital area."
In one of the more bizarre findings of the study, Long said the
fishes probably copulated from a sideways position with their bony
jointed arms locked together -- making them look more as if they
were square dancing than having sex.
"This enabled the males to maneuver their genital organs into the
right position for mating," he said.
(Editing by Ruth Pitchford)
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