A groundbreaking discovery has emerged from an international collaboration of Earth scientists, evolutionary biologists, and paleontologists: the unearthing of an ancient frog carrying a belly full of eggs, marking the oldest find of its kind. Published in Proceedings of the Royal Society B, the team's paper sheds light on the frog's characteristics, its origin, its estimated age, and its place within the frog family tree.
Previous studies have revealed that female frogs bear eggs in their bellies, eventually laying and fertilizing them with the help of males. In this latest investigation, the researchers stumbled upon a fossilized frog nestled within the Zhonggou Formation of the Hanxia outcrop. Dating techniques pinpointed its origin to the Lower or Early Cretaceous period, suggesting an existence roughly 100 million years ago, amidst the reign of dinosaurs.
Employing advanced CT scanning, the team scrutinized the fossil, uncovering its identity as Gansubatrachus qilianensis. Surprisingly, despite being not yet fully mature, the frog harbored a clutch of eggs within its abdomen, some of which were in the midst of being laid—a revelation unprecedented in ancient amphibians.
The X-ray examination confirmed the frog's reproductive capability, despite its skeletal immaturity, marking a significant finding in evolutionary biology.
The researchers ruled out natural causes such as old age or environmental disturbances in the water source as factors contributing to the frog's demise. With few other frog fossils found in the vicinity, environmental crises were also discounted.
The team speculated that the frog's demise may have been attributed to suffocation, potentially induced by the relentless behavior of a male companion. Previous studies have shown that male frogs engage in prolonged amplexus, embracing females to prevent them from moving, thus ensuring fertilization. In some instances, this embrace can last for hours or even days, exerting excessive strain on the female, leading to exhaustion or suffocation.
The findings offer a glimpse into the ancient reproductive behaviors of frogs and provide invaluable insights into the evolutionary journey of these fascinating amphibians.