Skip to navigation | Skip to content

Penis evolved millions of years ago


The colour image of the fossil (top), with the penis protruding from its underside. The fossil looks remarkably like its modern counterpart (bottom) (Science)

The penis evolved at least 425 million years ago, according to a new report of the world's oldest unequivocally male fossil found exquisitely preserved in the U.K.

The rare fossil of the small sea creature, a sort of cross between a shellfish and a prawn, known as an ostracode, retains very fine details. These include soft body parts, such as gills and a "stout" copulatory organ, according to a report in today's issue of the journal Science.

"The whole animal is amazing," said Professor David Siveter, the University of Leicester palaeontologist who led the study. "We've got something we could only dream about."

The researchers named the previously unknown species as Colymbosathon ecplecticos, Greek for "amazing swimmer with large penis". They found the fossil in Silurian-age rocks derived from fine volcanic ash, in Herefordshire.

The researchers used a way of looking at the fossil that had only been used a few times, and never before on such an ancient animal.

Researchers progressively shaved layers from the fossil and photographed them. They stored each photograph in a computer and later electronically assembled them to produce a sharp and detailed three-dimensional fossil image.

The image revealed fossilised soft appendages protruding from the animal's hinged shell and also from its internal structures.

The researchers identified its entire disgestive tract; limbs used for sensing, feeding, and swimming; a grasping appendage probably used to gather food; and six pairs of gills.

The also found its penis, confirming that these animals, and presumably others at the time, reproduced sexually.

The find pushes back the earliest described evidence for the soft-tissue anatomy of this important group of living crustaceans by almost 200 million years.

Fossil ostracode shells are so common and diverse that geologists use them to date and analyse ancient rocks.

Modern ostracodes are found in most aquatic environments worldwide and mostly scavenge dead organic matter. Few Silurian-age animals survived and even fewer have living relatives.

The scientists also realised that although this particular species has long been extinct, the five-millimetre fossil was remarkably similar to some living ostracodes, with a basic body plan that has changed very little over time. Its organs and other body structures are easily recognisable in its modern-day counterparts.

This past-and-present likeness suggests an extremely low rate of evolutionary change over the last 425 million years, a rarity in itself.

"I was flabbergasted," said Dr Koen Martens, a zoologist at the University of Amsterdam in the Netherlands, in a related news report in the journal.

"This is a demonstration of unbelievable stability," said Dr Tom Cronin of the U.S. Geological Survey in Reston, Virginia, in the same article. Whereas ostracodes have diversified into some 33,000 living and extinct species, "these guys have just been plodding along totally unfazed".

The Herefordshire specimens may reveal other long-lost evolutionary blueprints, said Dr David Horne of Queen Mary College in London.

"The probability that they will find similarly preserved representatives of other ostracode lineages, and of other arthropods, is both high and extremely exciting."

Tags: science-and-technology, archaeology, palaeontology