The platypus already seems determined to keep zoologists busy.

It is a mammal that lays eggs. It has a broad bill, webbed feet and dense fur. Males possess venom-delivering spurs on their hind legs. A perfectly ordinary afternoon in Australian natural history.

Then the fossil record adds teeth.

In 2013, researchers described Obdurodon tharalkooschild from a distinctive fossil molar found at Riversleigh in Queensland. The tooth belonged to an extinct platypus relative with a much more substantial chewing apparatus than the living species.

Adult modern platypuses lack teeth, processing food with tough pads in their mouths. Obdurodon retained functional teeth into adulthood.

The researchers estimated that this extinct animal may have reached about a metre in length. That reconstruction rests on limited material, so we should picture a plausible giant rather than a neatly measured museum specimen.

Its powerful tooth suggested a diet that could have included crustaceans and small vertebrates. Fish, frogs and small turtles were among the possibilities proposed by the team—not a confirmed list of fossil stomach contents.

The discovery also complicated an older picture of platypus evolution as a simple progression towards smaller bodies and reduced teeth. Here was evidence of a substantial side branch: a large animal with well-developed teeth, unlikely to have been the immediate ancestor of the living platypus.

That is one of the pleasures of palaeontology. A familiar animal becomes stranger as we learn more about its relatives.

The living platypus has plenty of surprises. Its fossil cousin arrived with extra chewing equipment.

Sources and Further Reading

• Giant extinct toothed platypus discovered — UNSW (2013).
• Platypus — Australian Museum.