Frogs formerly coexisted with dinosaurs. The North Sea covered half of Germany 45 million years ago. It’s astounding to believe that these tiny organisms survived the annihilation of the dinosaurs. However, a lower degree of mass death did occur in what is now known as the Geiseltal region of central Germany, and the cause has long been unknown.
Hundreds of frog fossils were discovered in a mass burial in Geiseltal’s 45-million-year-old swampy coastlands, and experts have been baffled as to why they were there for decades. However, my research team discovered an explanation: they perished from tiredness when mating.
We also discovered evidence that current frog and toad mating behavior stretches back at least 45 million years, as mass grave frog fossils from other sites display similar traits on the skeletons as the Geiseltal specimens.
What we discovered
The prehistoric frog skeletons were analyzed by my Irish-German research team. We, the paleontologists, photographed, drew, and studied the fossils. We counted how many bones remained in place and which bones and joints remained linked.
With this information, we were able to figure out what occurred to the frog skeletons after they died and why. Our investigation also discovered several skeletons in a single sediment layer, indicating that the majority of the petrified frogs died in mass mortality events (recurring events during which many hundreds of frogs died in a short time).
Other scientists believed the Geiseltal frogs and toads die
d as lakes dried up and oxygen levels plummeted. However, our analysis indicated that this was improbable because the frogs could have easily found their way to neighboring bodies of water. We also discovered evidence that the frog carcasses floated in the water for a while before sinking to the lake bottom. As a result, the lake did not dry up.
When we compared Geiseltal bones to modern frog skeletons, we discovered that most Geiseltal frogs were toads. Toads live primarily on land, except when they return to ponds to breed. They mated with a large number of other toads during the very short mating season, which lasts only a few hours in certain current tropical species.
For modern toad and frog species, sex can be a death trap. People are frequently overtaken by weariness and drown. Female frogs and toads are more likely to drown because they are frequently submerged underwater by one or more males. Toad graveyards can still be seen along migration routes and around or in mating ponds nowadays. This was most certainly the case with the Geiseltal specimens.
The carcasses were carried by light currents in the swampy lakes and sunk to the bottom in the lake’s cold, deep, and undisturbed areas. The chilly temperatures (possibly around 8°C) prevented decomposition and preserved several skeletons. Even little bones, such as finger or toe bones, are highly delineated in some skeletons.
Some frogs may have died from freezing, infections, or old age. Because these three reasons for death are difficult to confirm, the frogs took this information with them to the grave. My team came to an amazing conclusion after months of researching these fossils and considering what we know about their lifestyles.
The most likely explanation for numerous groups of frogs, each numbering in the hundreds, dying practically simultaneously in various ponds is that their eager mating killed them. It explains why comparable mass graves have been discovered throughout the world.
For decades, the German Geiseltal fossil collection remained closed, but it was recently reopened to the public and experts. It’s a remarkable time capsule of over 50,000 fossils from the Geiseltal’s former lignite (brown coal) opencast mine.
Crocodiles, gigantic snakes, giant flightless birds, and dog-sized primeval horses are among the relics. Many of the Geiseltal fossils are so well preserved that they reveal amazing details such as bones, scales, skin, internal organs, and gut contents.
In the early 2000s, the mine was flooded to create a recreational area, and it is now a massive lake.
Frogs should not be taken for granted.
While mating deaths may seem excessive, humans are a far more prevalent cause of frog and toad mortality, destroying their homes, contaminating water sources, and transmitting illness.
Frogs and toads have survived multiple global temperature changes and extinction events. Some species, however, have become extinct. One of the last remaining frog species of an old amphibian lineage was pronounced certainly extinct in 2021 after not being sighted in 60 years.
According to a 2019 UN report, amphibians, particularly frogs, are among the most vulnerable to ecological disasters. If the environmental circumstances in their pond change, frogs can travel a short distance. They are, however, prone to sickness, which can be caused by human impacts on nature.
Frogs and toads can be found almost anywhere, including trees, flowers, the jungle, and the desert. Some are nearly as colorful as a rainbow, and some can even fly. Consider these creatures dining alongside a T-Rex. Any further extinctions would be a tragedy.
Daniel Falk, a Ph.D. candidate in Geology and Palaeontology at the University College Cork, wrote this paper. It is reprinted with permission from The Conversation under a Creative Commons license.