Evidence Found for World's Earliest Vertebrate Sex

May 29, 2008

Sex as we vertebrates know it first happened at least 380 million years ago. We're talking way back. That's when insects first emerged, and fishes, sharks and rays had only been on the scene for a short while.

The evidence for this earliest critter-with-a-backbone mating comes by way of an extinct female fish found with her embryo still connected to her body by an umbilical cord. The poor fish, called a placoderm, must have died while giving birth, and that brief moment in time has now been preserved over the millennia. It shows that advanced reproductive biology was already underway at this very early period. It was comparable to the way some modern sharks and rays still reproduce today, proving the old adage that "if it isn't broke, don't fix it."

John Long, head of sciences at the Museum of Victoria in Melbourne, Australia, made the discovery with his colleagues.

Long told Reuters, "It is not only the first time ever that a fossil embryo has been found with an umbilical cord, but it is also the oldest known example of any creature giving birth to live young. It dawned on me after studying the specimen that this was the earliest evidence of vertebrates having sex by copulation, not just spawning in water."

He added, "This is the first bit of evidence on how a complete extinct class of animals may have reproduced."

Long explained that placoderms were a large and diverse group of fishes, thought to be the most primitive known vertebrates with jaws.

Here's what the actual fossil looks like (Image credits: Museum Victoria) :

And here's a modern recreation:

Comments

[Kate]

I feel like an idiot, but I can't "see" anything in the fossil. Jen, it would be oh so helpful (for those of us not used to looking at fossils) if what we are looking for was outlined somehow.

[Jen Viegas]

Hi Kate- No need to feel like an idiot. I think only a very well trained archaeologist could decipher the jumble of bones seen in the fossil pic. Sometimes these photos come with outlines and labels, but not this particular image. You can, however, see a video (that has a brief skeletal cutaway at the beginning) as well as a labeled outline for a similar skeleton, at
http://news.bbc.co.uk/2/hi/science/nature/7424281.stm
Thanks for your note!
Jen