A 45 million-year-old mystery involving the death of hundreds of fossil frogs has finally been solved.
Paleontologists from University College Cork (UCC) in Ireland made the discovery after studying the bones of the fossil frogs, which revealed that the ancient amphibians had died during mating. The phenomenon, which still occurs today for aquatic species, occurred in the Geiseltal Eocene conservation deposit in central Germany.
Where the ancient frogs lived
The area, once home to swampy forest, was a site of now-extinct plants and animals that inhabited Earth between 48 and 41 million years ago. According to the study, little is known about the area despite its rich flora and fauna.
A warmer climate made the area an ideal home for over 50,000 species, including ancestors of the horse, large crocodiles, giant snakes, lizards, birds, and anurans — frogs and toads.
Previous studies had developed various hypotheses about the death of the frogs, including desiccation of lakes, water oxygen depletion, poisoning by algal blooms, freezing, and starvation.
However, the study — led by Dr. Daniel Falk and Professor Maria McNamara in partnership with Martin- Luther- University Halle- Wittenberg— found that the frogs were healthy when they died, and concluded that the probable cause of death was drowning during mating.
What do the findings mean?
"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," explained Falk. "By process of elimination, the only explanation that makes sense is that they died during mating."
A female frog may drown when a male is on top of her, according to the study. Death can be the cause of sheer exhaustion from the physical labor that mating in water requires.
What are some other theories?
Another theory, dubbed “explosive breeding,” occurs when many males gather and compete for female mates in very short windows of time — sometimes being reduced to only a couple of hours a year.
These findings — which are among the first new discoveries made since the reopening of the Geiseltal fossil collections open to the public — help explain phenomena which is still common in frogs today.
“What’s really interesting is that fossil frogs from other sites also show these features, suggesting that the mating behaviors of modern frogs are really quite ancient and have been in place for at least 45 million years,” said McNamara.
“What’s really interesting is that fossil frogs from other sites also show these features, suggesting that the mating behaviors of modern frogs are really quite ancient and have been in place for at least 45 million years.”
Professor Maria McNamara