An incredibly preserved fossilized frog, dating to over 100 million years ago, has been discovered in China. Not only is it the oldest such frog ever found, but it still has a belly full of eggs, offering palaeontologists a fascinating snapshot in time and a rare glimpse into the species’ life history.
The team behind the discovery believe the unfortunate amphibian may have met its untimely end during mating, perhaps being drowned by an amorous male.
The frog was found in a fossil bed in the Jiuquan Basin of northwest China, which has been dated to the Lower Cretaceous period some 145 million to 100.5 million years ago. The find is especially impressive given that frogs from this era are rarely found in the fossil record, particularly those with soft tissues or eggs preserved.
Reconstructing the frog’s body using computed tomography (CT) scans of the fossils, the researchers determined that it likely belonged to the species Gansubatrachus qilianensis.
Despite being skeletally immature, the frog had egg masses in its body and eggs in its oviduct, which means that sexual maturation occurred before adulthood, something that, while common in non-avian vertebrates, is scarcely documented in the fossil record. Bettering our understanding of early frogs' reproductive strategies with findings like this could shed some light on their evolutionary history, lead author Baoxia Du told Live Science.
Frogs in this state, with a batch of eggs ready to be laid, are known as “gravid”. Since they don’t get pregnant, they will eventually lay the eggs, which are then fertilized by a male. However, in this case, things didn’t get that far.
The ill-fated amphibian expired before her eggs could be laid – but why?
“The primary causes of death of extant adult frogs are environmental stress, predation, starvation during hibernation, mating behaviour and old age,” the authors write in their study. However, they add, there were no signs of predation or advanced age, and the presence of multiple eggs suggests that the frog was neither hibernating nor starving. They also ruled out environmental factors as unlikely.
Instead, they conclude, “the most likely cause of death [...] is drowning or exhaustion in relation to mating,” which would make this “the first Mesozoic case of death linked to mating behaviour”.
She wouldn’t be the first amphibian to give up the ghost in the throes of passion – who could forget the ancient sex swamp death trap that took the lives of hundreds of horny frogs in Germany 45 million years ago?
If only she’d faked her own death, she might have lived to croak another day.
The study is published in Proceedings of the Royal Society B: Biological Sciences.