London: Turtles, who were killed as they were having sex and then fossilised in their position, have been described by scientists.
The remains of the 47-million-year old animals have been discovered in the famous Messel Pit near Darmstadt, Germany.
The animals were found as male-female pairs. In two cases, the tails of the males were tucked under their partners’ as would be expected from the coital position.
Researchers believe that the turtles had initiated sex in the surface waters of the lake that once existed on the site, and were then overcome as they sank through deeper layers made toxic by the sudden release of volcanic gases.
The animals, still in embrace, were then buried in the lakebed sediments and locked away in geological time.
“We see this in some volcanic lakes in East African today,” the BBC quoted Dr Walter Joyce of the University of Tubingen, as saying.
“Every few hundred years, these lakes can have a sudden outburst of carbon dioxide, like the opening of a champagne bottle, and it will poison everything around them,” he said.
The turtles, who belong to the extinct species Allaeochelys crassesculpta, are about 20cm in length; the females are slightly bigger than the males.
Their nearest living relatives are probably the pig-nosed turtle (Carettochelys insculpta), a much bigger species that swims in waters around Australia and Papua New Guinea.
A. crassesculpta is just one of thousands of exquisitely preserved fossil creatures pulled from Messel Pit, which has Unesco World Heritage status due to its palaeontological significance.
Nine pairs of turtles have been uncovered at the site over the past 30 years.
In most of the couples, the individuals were discovered in contact with other. For the pairs that were not, the individuals were no more than 30cm apart.
“People had long speculated they might have died while mating, but that’s quite different from actually showing it,” Dr Joyce said.
“We’ve demonstrated quite clearly that each pair is a male and a female, and not, for example, just two males that might have died in combat.
“This fact combined with the observation that their back ends are always orientated toward one another, and the two pairs with tails in the position of mating - that’s a smoking gun in our view,” he added.
It is apparently the only example in the fossil record of vertebrates being preserved in the act of having sex.
Details are carried in the Royal Society journal Biology Letters.