A 30-year-old bone discovery in southeastern Australia has sparked a new perspective on the evolution of echidnas and platypuses. The UNSW-led analysis of the Kryoryctes cadburyi humerus, found at Dinosaur Cove, suggests that ancient echidnas lived in water, contradicting the long-held theory that they evolved from land-dwelling ancestors.
According to lead author Emeritus Professor Suzanne Hand, there are about 30 instances where mammals transitioned from land to aquatic lifestyles, such as whales and dolphins. However, it’s extremely rare for mammals to evolve from semi-aquatic to terrestrial creatures. The researchers believe echidnas may have started as semi-aquatic animals that later adapted to life on land.
The analysis of the fossil revealed an internal structure more similar to platypuses than echidnas, indicating that Kryoryctes cadburyi was likely a semiaquatic mammal. This finding adds weight to the idea that stem-monotremes began as semi-aquatic animals and later transitioned to terrestrial environments.
The researchers also discovered other unique features in modern echidnas that could be linked to their semi-aquatic past, including sensitive receptors on the platypus bill and reversed hind feet similar to those of platypuses. A study of a respiratory protein called myoglobin in mammals suggests that echidnas may have had a semi-aquatic ancestry.
To further investigate this ancient mystery, the researchers plan to examine the microscopic anatomy of Kryoryctes using powerful scanning techniques. This research has implications for our understanding of monotreme evolution and highlights the importance of continued investigation into Mesozoic opalized fossils.
Source: https://phys.org/news/2025-04-extremely-rare-event-bone-analysis.html