A team of Irish scientists has solved an ancient mystery to reveal from 45 million-year-old fossils that thousands of prehistoric frogs likely died in a swamp sex trap.
paleontologists from niversity College Cork (UCC), led by Dr Daniel Falk and Professor Maria McNamara, were part of an international team studying fascinating fossils from the Geiseltal area of central Germany.
The area is one of the world’s richest fossil deposits – with the ancient swamp containing the remains of over 50,000 birds, horses, bats, fish and frogs.
Hailed as a mid-Eocene treasure trove, the fate of thousands of frogs in the fossil record has baffled scientists for decades.
About 50 million years ago the Earth was much warmer and the Geiseltal area was a swampy subtropical forest.
In addition to birds, frogs, and bats, the area was also populated by an ancient ancestor of the modern horse, large crocodiles, giant snakes, and lizards.
Previous studies had shown that the frogs died during a period of lake drying or severe oxygen depletion in the water.
How exactly the frogs died, however, was a mystery.
The UCC team conducted a painstaking analysis of the bones — and came up with their death-of-death theory.
“As far as we can tell, the fossil frogs were healthy when they died, and the bones show no signs of predators or scavengers — nor is there any evidence that they washed up during floods or died because the swamp dried up,” he said. Dr Falk.
The Geisel Valley fossil frogs were of a species that spent their lives on land, returning to the water to breed only during the mating season.
“Through the process of elimination, the only logical explanation is that they died while mating.”
Such a death-of-death theory is not uncommon for frogs going mad during the short, intense mating season.
“Female frogs are at greater risk of drowning because they are often submerged by one or more males — this often happens in species that mate during the short explosive breeding season,” explains Professor McNamara.
“What’s really interesting is that fossil frogs from other sites also exhibit these characteristics, suggesting that the mating behavior of modern frogs is really very old, dating back at least 45 million years.”
The UCC team’s findings came to light after the reopening of the Geiseltal fossil collections of the Zentralmagazin Naturwissenschaftlicher Sammlungen (ZNS) in Halle, Germany.
The Irish team worked as part of a collaborative project with researchers from Martin-Luther University in Halle-Wittenberg.
The full details of the study and its conclusions are published today in the prestigious journal “Paleontology.”