Australia's short-beaked echidna looks nothing like the platypus, but a new DNA analysis suggests that echidnas may have rapidly evolved from a platypus-like animal between 30 and 15 million years ago.
Credit: Wikimedia
SYDNEY: New research suggests that the echidna may have evolved from a platypus-like animal, sometime in the last 30 million years. The discovery may explain a confusing lack of echidnas in the fossil record.
Monotremes were thought to be "remnant, relic survivors from the past" that have evolved little in over 100 million years, said lead author Matthew Phillips, a molecular biologist at the Australian National University, in Canberra. But we now have evidence that this is not at all the case, he said.
Turning a theory upside down
The study is published this week in the U.S. journal the Proceedings of the National Academy of Sciences (PNAS).
In 2008, a reanalysis of platypus-like fossils that were over 100 million years old suggested that the platypus and echidna lineages had diverged before that time. The new study may turn this theory on its head.
To make the analysis, Phillips and his team used DNA sequences from both the modern platypus (Ornithorhynchus anatinus) and Australia's short-beaked echidna (Tachyglossus aculeatus).
Using an analytical method called the 'molecular clock' they were able to compare the rate of change in these DNA sequences over time and estimate when the animals last shared a common ancestor.
Not a living fossil
With this method they found evidence that the species last shared an ancestor as recently as around 30 million years ago (with a range of 19 to 48 million years ago). This animal was similar to the modern-day platypus, Phillips told Cosmos Online. "It's interesting because since then the platypuses have gone on being platypuses whereas echidnas have evolved rapidly into a different ecological niche."
Therefore, "monotremes are not just living fossils as they've been thought to be," he said, but instead continued to evolve despite having to compete with marsupials who first appear in the Australian fossil record around 60 to 70 million years ago.
The findings also explain the perplexing problem of why echidna fossils do not appear in the record until 15 million years ago.
"An entirely unique body for the echidna must have evolved relatively rapidly within the fifteen-million years interval", said Gavin Prideaux, a palaeontologist at Flinders University in Adelaide, South Australia, who was not involved with the research.
