The platypus and echidna, often regarded as some of the most peculiar animals on Earth, may be hiding a far more complex evolutionary story than scientists initially believed. Recent findings from a groundbreaking study have unveiled new insights into these enigmatic creatures.
The Fascinating World of Monotremes
Native to Australia and New Guinea, the platypus and echidna are two of the only remaining monotremes—mammals that lay eggs instead of giving live birth.
These creatures exhibit strange characteristics that set them apart from other mammals. The platypus, an amphibious animal, has a bill and webbed feet like a duck.
The echidna, known for its spiny exterior, is a strictly terrestrial creature, spending its days burrowing in the ground and feeding on ants and termites.
Both animals produce milk, but rather than using nipples, they secrete it through their skin, where their young (called puggles) lap it up.
Dr. Guillermo W. Rougier, a professor of anatomical sciences at the University of Louisville, notes, “They are one of the defining groups of mammals. The typical mammal from the time of dinosaurs probably shared a lot more biology with a monotreme than with a horse, a dog, a cat or ourselves.”
The Groundbreaking Fossil Discovery
The turning point in this new understanding came from a long-lost fossil. In 1993, a single bone—a humerus (upper arm bone)—was discovered at Dinosaur Cove, a remote site in southeastern Australia.
While the fossil initially seemed to resemble that of a land-dwelling ancestor of the echidna, closer analysis revealed something far more intriguing.
By utilizing advanced 3D imaging techniques, the research team uncovered features inside the fossil that suggest a semi-aquatic lifestyle.
The internal structure of the fossil bone was thicker and had a smaller central cavity, traits that are typically found in aquatic animals to help them dive and stay submerged.
“By using advanced 3D imaging approaches, we have been able to illuminate previously unseen features of this ancient bone, and those have revealed a quite unexpected story,” said Dr. Laura Wilson, an associate professor at Australian National University and co-author of the study.
These findings support the idea that Kryoryctes cadburyi, the ancient ancestor from over 100 million years ago, may have been a common ancestor for both the platypus and the echidna.
Evolution from Water to Land
The study, published Proceedings of the National Academy of Sciences, challenges the conventional understanding of the platypus and echidna’s evolution.
“Our study indicates that the amphibious lifestyle of the modern platypus had its origins at least 100 million years ago,” said Suzanne Hand, a professor emeritus at the University of New South Wales and lead author of the study. “And that echidnas made a much later reversion to a fully terrestrial lifestyle.”
The echidna’s backward-facing feet, which have always been an oddity, could be a result of its ancient aquatic past.
According to Dr. Hand, these feet may have evolved from an ancestor that used its hind legs as rudders for swimming, an adaptation that carried over even when the echidna became a land-dwelling creature.
Monotremes: A Glimpse Into Mammalian Evolution
Monotremes offer a fascinating glimpse into the early evolution of mammals. These creatures represent a branch of the evolutionary tree that diverged from other mammals more than 180 million years ago.
Dr. Rougier explains, “Monotremes are these living fossils from a very long distant past. You and a platypus probably had the last common ancestor over 180 million years ago.
There is no way to predict the biology of this last common ancestor without animals like monotremes.”
The findings also raise questions about the broader evolutionary patterns of mammals.
