The oldest known penis-like structure has been discovered in a 400 million year old fossilized fish by a team of scientists led by paleontologist Doctor John Long.

The clasper, as it is called, was actually discovered in Western Australia in 2001, but was thought to be part of the pelvic girdle, partly because it was thought that ancient fish fertilized their eggs outside of the female.

But when two fossilized female fish were found carrying embryos earlier this year, the pelvic girdle was re-examined, and discovered to be a penis.

“It's a pretty big find because placaderms were the dominant fish for 70 million years, but we knew nothing about their reproduction,” says Long.

Sperm funnels through the clasper, made of actual bone, while the male placoderm uses an extra fin to grip onto the female. This is similar to how modern sharks copulate, suggesting the placoderms had very advanced reproductive systems.

Study author and paleontologist Kate Trinajstic added that scientists could now identify the sex of ancient fish, something they could not do before.

Regarding the clasper itself, “We were surprised because it's so big," says Trinajstic. "We were expecting something smaller.”

http://www.abc.net.au/science/articles/2009/07/14/2621203.htm

http://www.manolith.com/2009/07/15/john-longs-ancient-fish-penis/

http://dsc.discovery.com/news/2009/07/14/oldest-male-organ.html

http://au.news.yahoo.com/a/-/newshome/5724099

http://dsc.discovery.com/news/2009/02/25/fish-sex-evolution.html