Researchers studying fossils unearthed in northwestern Queensland have discovered a new family of carnivorous marsupials that lived 15 million years ago. They enjoyed ancient escargot thanks to a massive shell-cracking tooth, according to findings published in Scientific Reports this week.
The "unusual hammer-toothed" marsupial Malleodectes mirabilis was first described in 2011 based on a partial left upper jaw (or maxilla). Its dental adaptations suggested that it crushed hard snail shells: thick enamel and a dome-like crown on its enormous P3 premolar that worked like a pestle or a ball-peen hammer.
"Uniquely among mammals, it appears to have had an insatiable appetite for escargot – snails in the whole shell," Mike Archer from the University of New South Wales said in a statement. "Its most striking feature was a huge, extremely powerful, hammer-like premolar that would have been able to crack and then crush the strongest snail shells in the forest." While it appears to be related to marsupial carnivores like Tasmanian devils or extinct Tasmanian tigers, it was never clear which, if any, known family it belonged to.
Now, a new Malleodectes mirabilis specimen (QM F57925) has been discovered in middle Miocene deposits of the Riversleigh World Heritage area at a 14.64-million-year-old cave site called AL90. The original entrance to the cave acted as a natural pit-fall trap, and there’s nothing left of the cave now except a limestone floor containing the bones of thousands of animals that had fallen in.
Maxilla of the young malleodectid found at Riversleigh. Because this is a juvenile, the massive premolar is still unerupted below the tooth row. Karen Black and Suzanne Hand/UNSW
The new fossil includes part of a skull, a fragmentary maxilla, and several teeth belonging to a juvenile that would have weighed an estimated 896 grams (2 pounds). Archer’s team examined the specimen using a micro-CT scanner. This juvenile was still teething, and its massive premolar was about ready to erupt.
Based on details of the canine, premolar, and molar teeth, the team allocated the marsupial to a new family they call Malleodectidae. The name is derived from the genus name Malleodectes, which combines "malleo," Latin for hammer, with "dectes," Greek for biter.
And while the new specimen still supports those previous shell-crushing interpretations, the team realized that the molars are far more substantial than originally thought. Some were even equipped with vertically-shearing blades. That means it’s possible that these marsupials enjoyed a wider diet that also included small vertebrates with bony skeletons.
"Malleodectes mirabilis was a bizarre mammal, as strange in its own way as a koala or kangaroo," Archer added. They occupied a niche in Australia’s Miocene rainforests that no other mammal group has managed to occupy since.