By Jonathan Amos
BBC News science reporter
A sculpted and polished phallus found in a German cave is among the earliest representations of male sexuality ever uncovered, researchers say.
The 20cm-long, 3cm-wide stone object, which is dated to be about 28,000 years old, was buried in the famous Hohle Fels Cave near Ulm in the Swabian Jura.
The prehistoric "tool" was reassembled from 14 fragments of siltstone.
Its life size suggests it may well have been used as a sex aid by its Ice Age makers, scientists report.
"In addition to being a symbolic representation of male genitalia, it was also at times used for knapping flints," explained Professor Nicholas Conard, from the department of Early Prehistory and Quaternary Ecology, at Tübingen University.
"There are some areas where it has some very typical scars from that," he told the BBC News website.
Researchers believe the object's distinctive form and etched rings around one end mean there can be little doubt as to its symbolic nature.
"It's highly polished; it's clearly recognisable," said Professor Conard.
The Tübingen team working Hohle Fels already had 13 fractured parts of the phallus in storage, but it was only with the discovery of a 14th fragment last year that the team was able finally to put the "jigsaw" together.
The different stone sections were all recovered from a well-dated ash layer in the cave complex associated with the activities of modern humans (not their pre-historic "cousins", the Neanderthals).
The dig site is one of the most remarkable in central Europe. Hohle Fels stands more than 500m above sea level in the Ach River Valley and has produced thousands of Upper Palaeolithic items.
Some have been truly exquisite in their sophistication and detail, such as a 30,000-year-old avian figurine crafted from mammoth ivory. It is believed to be one of the earliest representations of a bird in the archaeological record.
Female forms, such as the 30,000-year-old Venus of Willendorf are more common
There are other stone objects known to science that are obviously phallic symbols and are slightly older - from France and Morocco, of particular note. But to have any representation of male genitalia from this time period is highly unusual.
"Female representations with highly accentuated sexual attributes are very well documented at many sites, but male representations are very, very rare," explained Professor Conard.
Current evidence indicates that the Swabian Jura of southwestern Germany was one of the central regions of cultural innovation after the arrival of modern humans in Europe some 40,000 years ago.
The Hohle Fels phallus will go on show at Blaubeuren prehistoric museum in an exhibition called Ice Art - Clearly Male.