Death met primeval turtles during mating

Palontologists discover the first fossils of copulating vertebrates in the Messel Pit

This is one of the nine copulating pairs of prehistoric turtles found in the 47 million year old oil shale of Messel Pit; The male is on the right and is slightly smaller than the female connected to it at the edge of the shield. © Senckenberg Natural History Museum Frankfurt
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Death overtook them during sex: for the first time paleontologists have discovered fossils of copulating vertebrates. In the Messel pit near Darmstadt, they came across a total of nine pairs of primeval softshell turtles, which had died during the mating and been preserved in this position. The hind ends of their shields were pressed together and the males had partially bent their cock under the female's shell and placed it next to their mate's. This is typical of the mating position. The finding of the copulating deceased tortoises also indicates how the animals once died in the former volcanic lake. Presumably, they had sunk during mating in deeper, poisonous layers of water of the lake and died quickly there, reports the German-Swiss research team in the journal "Biology Letters". In addition to paleontologists from the Universities of Tübingen and Zurich, scientists from the Senckenberg Research Institute in Frankfurt and the Hessian State Museum Darmstadt are among them.

The Messel Pit is one of the UNESCO World Heritage Sites due to its rich fossil record. In the oil shale deposits of the former volcanic lake are numerous relics of animals and plants from around 47 million years ago. In the Messel oil shale, the researchers also found a total of 51 specimens of soft-shelled turtles Allaeochelys crassesculpta, 18 of which were kept as a pair. "This find is of great significance for the entire fossil history of the Messel pit, " say the paleontologists. Because the copulating turtle pairs speak against previous scenarios for the death of primeval animals in the former volcanic lake.

Another pair of prehistoric turtles that died 47 million years ago during mating and were conserved in the slate of the Messel Pit; The male is on the right and is slightly smaller than the female connected to it at the back of the shield. Senckenberg Nature Museum Frankfurt

Neither poisonous volcanic gases nor algal blooms as a cause of death

Previously, it was thought that the lake periodically emitted toxic volcanic gases, or that toxic algal blooms in summer poisoned the drinking water of animals living in and around the lake. However, neither of these two scenarios can explain why the turtles died in mating: "It is implausible that the turtles voluntarily swim in poisonous water to woo their partners and themselves then eventually mate there, "say Walter Joyce of the University of T bingen and his colleagues. It is therefore extremely unlikely that there was a poisonous algae blooms in the lake during the mating season of the turtles.

According to the researchers, the death of the copulating turtles indicates a very different scenario: "If a turtle males have successfully mounted a female, the pair usually remains motionless in the water for a considerable time, " explains Joyren Joyce and his colleagues. The pair may sink to considerable depths. They therefore suspect that the prehistoric turtles in the nontoxic surface water of the lake began their mating, but then sank into deeper, poisonous layers of water.

The deep water toxic by volcanic gas or organic deposits has been deadly to the animals, the researchers say. For the skin of today still alive and most likely also of the primeval softshell turtles was unarmored and relatively permeable, because these animals also breathed over the skin. At the bottom of the lake, the dead male slipped down from the backs of the females and their fossils settled side by side - as they were now found. (doi: 10.1098 / rsbl.2012.0361) Display

(Biology Letters, 20.06.2012 - NPO)