Long before the platypus, 100 million years ago, several species of egg-laying mammals inhabited Australia. This is the finding of a new report published in Alcheringa: Australian Journal of Paleontology. The study reveals six types (three of which are completely new to science) of fossils found at Lightning Ridge.
Information refers to a period that was called the “Age of Monotremes.” Currently, these egg-laying mammals have been almost completely replaced by marsupials and placental mammals. Only two families survive: the platypus and the echidna, and they are restricted to Australia and New Guinea.
The fossils have been in the Australian Museum’s collection for decades, but have only now been properly classified and studied.
As a result, the six types of monotremes identified by archaeologists are:
- Opalius is great
- Steurtodon elizabeth
- Collicodon Richie
- Stereopodon galmanii
- Parvobalus cleitiii
- Daragara dawn
“There are four species known from a single specimen, indicating that the diversity is still underrepresented. This discovery adds more than 20% to the previously known diversity of monotremes,” say the archaeologists.
The species is monotreme
One of the newly discovered species, Opalius is amazing! It shares characteristics with both echidnas and platypuses. It was placed in a new family called Opalionidae.
Another, called Daragara dawngained fame due to a jaw very similar to that of the modern platypus.
One of the great mysteries of monophyletic evolution is when exactly platypus and echidnas diverged from a common ancestor. Genetic evidence suggests this happened about 50 million years ago.
Mammals that lay eggs
The oldest evidence we have of platypus ancestors is 60 million years old. And all thanks to the geological formation of Argentine Patagonia.
Monotremes come from a very ancient lineage of mammals. They share characteristics with early mammals and reptiles, having inherited this ability to lay eggs.
This characteristic is an ancestral trait dating back to the first amniotes, the common ancestors of reptiles, birds and mammals.
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