An ancient swamp was a deadly sex trap for fossil frogs

An ancient swamp was a deadly sex trap for fossil frogs

An ancient swamp is a deadly sex trap for fossil frogs

Well-preserved skeleton of a fossil frog from the Geiseltal collection. The frog probably died while mating in a swampy environment and broke into two pieces due to currents on the bottom of the lake. Credit: D. Falk.

University College Cork (UCC) paleontologists have discovered why hundreds of fossil frogs died in an ancient marsh 45 million years ago: It happened during mating.

The aquatic death trap in the Geiseltal region of central Germany claimed the lives of more than 50,000 ancient beasts, including birds, horses, bats, fish and hundreds of frogs. Due to its unique geological features and thousands of fossils, the former Geiseltal coalfield in Saxony-Anhalt is considered a scientific treasure trove, providing a unique window into the evolution of Earth’s plants and animals over the of millions of years.

Nearly 50 million years ago – the Middle Eocene – the Earth was much warmer and the Geiseltal region was a swampy subtropical forest whose inhabitants included ancestors of the horse, large crocodiles, giant snakes, lizards, land birds and many anurans, which are frogs and toads.

Previous studies have suggested that Geiseltal frogs died when lakes dried up and/or oxygen in the water was depleted. But what killed these creatures has long been a mystery, until now.

By studying the bones of fossil frogs, the UCC team was able to narrow down the options. “As far as we can tell, the fossil frogs were healthy when they died, and the bones show no signs of predators or scavengers – there is also no evidence that they were taken away during the floods or that they died because the marsh dried up,” said Daniel Falk, a UCC researcher and leader of the study. Furthermore, most of the fossil frogs in the Geiseltal are species that spend their lives on land and only return to water to reproduce. “By process of elimination, the only explanation that makes sense is that they died during mating.”

  • An ancient swamp is a deadly sex trap for fossil frogs

    The frog skeleton shows exceptional completeness and articulation (false colors). 1 credit

  • An ancient swamp is a deadly sex trap for fossil frogs

    Geiseltal frog taphonomy at a glance. 1 credit

This phenomenon is common among frogs today. “Female frogs are at a higher risk of drowning because they are often overwhelmed by one or more males – this often occurs in species that engage in mating congregations during the short explosive breeding season,” said lead author, Professor Maria McNamara. “What’s really interesting is that fossil frogs from other sites also show these characteristics, suggesting that modern frog mating behaviors are really quite ancient and have been in place for at least 45 million years. years.”

The research has been published in Articles in paleontology.

A long history of European geckos

More information:
Falk et al, “Skeletal taphonomy of anurans from the Eocene Geiseltal Konservat-Lagerstätte, Germany: overview of controls on the preservation of fossil anurans”, Articles in paleontology (2022). DOI: 10.1002/spp2.1453

Provided by University College Cork

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