100-million-year old frog with eggs in its belly discovered in China

A snapshot of life from 100 million years ago has been captured after the fossil of a frog with eggs in its stomach was discovered.

It’s a remarkable find, especially given that fossils from the time period are rarely so well preserved.

The find was made in a fossil bed in the Jiuquan Basin of northwest China. The bed is dated from around 145 million to 100.5 million years ago, back in the Lower Cretaceous period.

The frog alone would be an insightful find, given it's the oldest frog fossil ever discovered, but the fact the female had eggs in its stomach makes it even more significant.

In fact, scanning the fossil authors of the study to confirm it was a frog from the species Gansubatrachus qilianensis.

Baoxia Du et al., Royal Society B: Biological Sciences, 2024

The researchers behind the study have also put forward a theory as to how the frog could have died. According to them, the frog may have been killed during mating.

Even rarer for fossils of this kind, this particular species of frog matured sexually before adulthood, laying eggs for males to fertilise.

The authors of the study, which is published in Proceedings of the Royal Society B: Biological Sciences, hope the discovery will lead to greater understanding of animal life cycles from the time period.

The study reads: “The primary causes of death of extant adult frogs are environmental stress, predation, starvation during hibernation, mating behaviour and old age.”

The authors then argue that “the most likely cause of death… is drowning or exhaustion in relation to mating” and that it marks “the first Mesozoic case of death linked to mating behaviour”.

It’s a remarkable discovery that brings home just how staggering the timescales of life on Earth are – home sapiens have only been around for about 300,000 years, but life has been around for 3.7 billion and even the humble frog was here more than 100 million years ago and we're learning new things about them all the time.

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