Bandicoots and bilbies are elusive in the fossil record. Not as famous as the koala or the kangaroo, fewer than 25 fossil species have been named.
The first fossil bilby ever recovered was discovered by an American palaeontologist in South Australia in 1955. It was 3.9 million years old and consisted of a single lower jaw with a few teeth and was described as a species dubbed Ischnodon australis. No other specimens of that species have been recovered since.
Despite many decades of fossil collecting around Australia, no other fossil bilbies were found until 2014. The WA Museum’s Curator of Mammals, Dr Kenny Travouillon, was researching fossils from the Riversleigh Word Heritage Area in Queensland when he spotted a few teeth, which turned out to belong to a primitive bilby.
The new fossil was about 10 million years older than Ischnodon australis. He named the new species Liyamayi dayi. Until now, that was the end of what we knew about fossil bilbies.
Reconstruction and fossil of the oldest bilby Bulbadon warburtonae. Art by George Aldridge. Photo by Kenny Travouillon.
We’ve done much better with bandicoot fossils. The first fossil bandicoot, Perameles allinghamensis, was discovered in 1976 in northern Queensland. Since then, more than 20 species of fossil bandicoots have been named, the bulk of which came from the Riversleigh area. The oldest bandicoot known to date, Bulungu muirheadae, was found in South Australia and is about 24.9 million years old.
The diversity of marsupials discovered at Riversleigh has massively increased our knowledge of their evolution.
Kenny recently spent time at the Eastern Washington University where he’d been invited to study bilby and bandicoot fossils collected in South Australia. The sites around Lake Eyre and surrounding lakes have produced some of the oldest fossil marsupials related to our modern species.
He was able to identify four new species. Two of these are the oldest known fossil bandicoot (Bulungu minkinaensis) and the oldest known bilby (Bulbadon warburtonae).
Once a new species is discovered, the next step is to work out how it is related to all other known species. This is done with a phylogenetic analysis, which produces a sort of family tree placing the most similar species close together.
Along with two colleagues, Kenny found that our oldest bandicoots were part of an ancient group of bandicoots that went extinct around 10 million years ago. In contrast, modern bandicoots have evolved more recently.
The world’s oldest bilby, however, confirmed previous genetic work showing that bilbies evolved around 30 million years ago.
Published on 12 August 2021
