A team of Irish scientists have solved an ancient mystery to reveal from 45 million year old fossils that thousands of prehistoric frogs likely died in a swamp sex trap.
niversity College Cork (UCC) palaeontologists, led by Dr Daniel Falk and Professor Maria McNamara, were part of an international team studying fascinating fossil records from the Geiseltal area of central Germany.
The area is one of the world’s richest fossil depositories – with the ancient swamp containing the remains of over 50,000 birds, horses, bats, fish and frogs.
Hailed as a treasure trove of the middle Eocene era, the fate of thousands of frogs in the fossil layer has baffled scientists for decades.
Some 50 million years ago, the Earth was much warmer and the area of Geiseltal was a swampy subtropical forest.
As well as birds, frogs and bats, the area was also populated by an ancient ancestor of the modern horse, large crocodiles, giant snakes and lizards.
Earlier studies had indicated that the frogs died during a period of lake drying or severe oxygen depletion within the water.
However, precisely how the frogs died was a mystery.
The UCC team undertook a painstaking analysis of the bones – and came up with their sex death trap theory.
“As far as we can tell, the fossil frogs were healthy when they died, and the bones don’t show any signs of predators or scavengers – there is also no evidence that they were washed in during floods, or died because the swamp dried up,” Dr Falk said.
The Geiseltal fossil frogs were of a species that spend their lives on land, only returning to the water to breed during the mating season.
“By process of elimination, the only explanation that makes sense is that they died during mating.”
Such a sex death trap theory is not unusual for frogs who become frenzied during the short, intense mating season.
“Female frogs are at higher risk of drowning as they are often submerged by one or more males – this often happens in species that engage in mating congregations during the short explosive breeding season,” Professor McNamara explained.
“What’s really interesting is that fossil frogs from other sites also show these features, suggesting that the mating behaviours of modern frogs are really quite ancient and have been in place for at least 45 million years.”
The UCC team findings came to light following the re-opening of the Geiseltal fossil collections of the Zentralmagazin Naturwissenschaftlicher Sammlungen (ZNS) in Halle, Germany.
The Irish team worked as part of a co-operative project with researchers from the Martin-Luther-University in Halle-Wittenberg.
Full details of the study and its conclusions will be published today in the prestigious journal, ‘Paleontology.’