Prehistoric Sex?

By Jennifer Viegas

updated 6/19/2012 11:18:48 PM ET

 

A 47-million-year-old fossil of nine turtle couples in the act of mating has been found.

The turtles, described in the latest Biology Letters, apparently died in the throws of passion. While deeply engaged in copulation, they drifted into poisonous water and perished, forever preserved in their lovemaking moment. 


“Many animals enter a trance-like state when mating or laying eggs and it is possible that these turtles simply did not notice that they were entering poisonous waters before it was too late,” lead author Walter Joyce, a researcher at the University of Tübingen, told Discovery News. 

Joyce and his colleagues analyzed the fossils, found in the Messel Pit Fossil Site between Darmstadt and Frankfurt, Germany. Numerous fossilized birds, bats, fish, frogs, snakes, insects and more were also found at the site, suggesting that at least some of them too were poisoned by what was, back in the Eocene, a volcanic lake.


The turtle couples did not all die together, but instead were found at random throughout the site of the former lake. The scientists can tell that each couple consisted of one male and one female due to tail shape and length differences, body size differences and other anatomical features. Females of this turtle species (Allaeochelys crassesculpta), for example, have a hinge in their belly shields that helped them lay relatively large eggs.

It is rare for any animal to die and be fossilized while engaged in a behavior. Other famous examples include fish that choked on large prey items and were later found fossilized in that moment. Certain dinosaurs died fighting or while brooding their nests. Such discoveries are invaluable to scientists because they reveal how animals behaved in the flesh, something that is normally just speculated upon.

“Millions of animals live and die every year and many enter the fossil record through serendipitous circumstances, but there really is no reason to enter the fossil record while you are mating,” Joyce said. “After all, the chances of both partners dying at the same time is highly unlikely and the chances of both partners being preserved afterwards even less likely.”


“The Messel turtles are therefore the only vertebrate fossils known to have died while in the process of mating and this only happened because of the highly unusual circumstances of the lake in which they lived,” he added.


The turtles initiated copulation in habitable water. They then may have gone into the intense “trance-like” state while sinking deeper into the lake. At that point, their skin probably started to absorb poisons from the build-up of volcanic gases or decay of organic matter.


According to the researchers, the mating pairs from Messel are therefore consistent with a stratified, volcanic lake with mostly inhabitable waters and a deadly abyss.


James Parham is an aquatic biologist and hydrologist at the Bishop Museum. He is also president of Parham & Associates Environmental Consulting. Parham agrees with the new study’s conclusions. He told Discovery News, “This is an excellent scientific treatment of some incredible fossil specimens.”
Tyler Lyson, director and president of the Marmarth Research Foundation, also told Discovery News that he supports the new study.


“The argument is strong and the conclusions sound,” Lyson said. “We see similar sexual morphism in living turtles and the fact that there are so many pairs of turtles indicates they were copulating, sunk and died in the more toxic waters.”