Echidna Ancestors: How Ancient Aquatic Lifestyles Shaped These Unique Creatures, Revealed by New Research

Platypuses and echidnas, found only in Australasia, are unique creatures. They’re the last surviving egg-laying mammals on Earth. While they share some traits, they’re quite different in how they live and thrive.

The platypus thrives in water, often spending 20 hours each day swimming to hunt for food like small invertebrates. In contrast, echidnas are terrestrial, mainly roaming Australia and New Guinea, and feast on ants, termites, and earthworms.

So, how did these differences come to be? Some scientists suggest that echidnas may have evolved from a water-loving ancestor resembling the platypus. This theory stems from their genes and anatomy but has faced skepticism due to a lack of fossil evidence—until now.

Recent research, published in PNAS, has uncovered new information from a bone dating back 108 million years. This humerus belonged to a species named Kryoryctes cadburyi, discovered at Dinosaur Cove in Victoria, Australia. It provides pivotal insight into the evolutionary journey from aquatic to terrestrial living.

Kryoryctes existed during the Mesozoic Era when monotremes were more prevalent. Today, we mostly find their fossils in the form of teeth and jaws, making this limb bone extraordinary and revealing.

To explore the evolutionary ties of Kryoryctes, researchers compared it to a comprehensive dataset of 70 fossil and modern mammals. The study revealed Kryoryctes is an ancestral monotreme. Interestingly, while its external bone structure resembled echidnas, its internal structure showed it shared features with the platypus.

These interior features imply that the arm bone belonged to a semi-aquatic creature, confirming the hypothesis of a semi-aquatic lineage for monotremes.

This discovery suggests that all living monotremes, including the platypus, may have originated from an ancestor that thrived in water over 100 million years ago. It seems the platypus has held onto its aquatic lifestyle, while echidnas returned to land more recently, adapting along the way.

Echidnas showcase several unique adaptations, such as lighter bones and changes in their physical features like a narrower beak and less webbing between their toes, likely a response to their return to land.

However, the timeline for when these changes occurred remains unclear, pending further fossil discoveries. The habitats of monotremes are increasingly at risk due to climate change, habitat destruction, and human interaction, particularly affecting the platypus population.

Understanding how these ancient animals have adapted is crucial for their survival, ensuring we protect their unique place in nature.