(Malleodectes (left) aka “Hammer-Biter” and the pink-tongued skink (right) are examples of convergent evolution, suggesting both were highly-specialized snail-eaters; Credit: Rick Arena and Scott Hocknull)
Meet “Hammer-Biter,” a newly discovered marsupial that lived 10 million to 17 million years ago and had hammer-like teeth similar to those seen in modern skinks, according to a paper in the latest issue of the journal Proceedings of the Royal Society B.
(Pink-tongued skink foaming at the mouth while crunching a snail; Image copyright: Steve Wilson)
Fossils for the “bizarre, lizard-like” prehistoric snail-eating marsupials (Malleodectes) were found in a field in the Riversleigh World Heritage area of Queensland, Australia.
“Hammer-Biter” possessed an enormous blunt tooth in each side of its upper jaw, according to study lead author Rick Arena.
“At first, the function of these teeth was a mystery because we were unaware of any other mammal that had hammer-teeth like this,” Arena, of the University of New South Wales Evolution of Earth & Life Systems Research Group, was quoted as saying in a press release.
(Excavating fossils at the Riversleigh World Heritage fossil area in north-western Queensland; Credit: Henk Godthelp)
Scott Hocknull of the Queensland Museum, however, noticed striking similarities to the modern pink-tongued skink, an Australian reptile.
“This rainforest skink has an almost identical giant, hammer-tooth in its dentition and in this case we know what it’s used for: crushing the hard shells of snails, one of the main foods of this rainforest skink,” said Hocknull.
Arena added, “It appears Malleodectes evolved millions of years ago to exploit the ecological niche occupied today by these specialised lizards.”
(A forest at Riversleigh in prehistoric Miocene times; Artist: Dorothy Dunphy)
The sync exemplifies evolutionary convergence. This is when species independently evolve comparable solutions to similar challenges. Despite the millions of years difference, the goal was the same in this case for each animal: to crush and swallow tasty snails.
While there are many examples of evolutionary convergence, Arena and his team say this is the first time a marsupial has been found with dental adaptations most closely resembling those of a lizard.
Malleodectes eventually bit the dust, becoming extinct 10 million years ago when the Australian continent experienced rapid climate change.
“It’s possible that species of Malleodectes may have survived for a bit longer in rainforest communities in eastern Australia and here found themselves in competition for snails with the similarly-specialized ancestors of the pink-tongued skinks,” said coauthor Mike Archer. “If this did happen, clearly, for whatever reason, these extraordinary mammals lost out to the lizards.”