First biofluorescent egg-laying mammal

The platypus (Ornithorhynchus anatinus) is the world's first-known biofluorescent species of egg-laying (monotreme) mammal. The fur of this species appears brown when viewed in normal, visible light. However, in October 2020 a study published in the scientific journal Mammalia revealed that when a research team shone invisible ultraviolet (UV) light with a wavelength of 200–400 nanometres (nm) upon three museum specimens of platypus, their fur glowed green or cyan, with a wavelength of 500–600 nm – a classic yet hitherto-unknown mammalian example of biofluorescence.

Biofluorescence is where visible light being re-emitted by these animals' fur had a longer wavelength (and shorter frequency) than the UV light that had been shone upon them.

After reading this paper just a few weeks after it had been published, curators at the Western Australian Museum illuminated their own preserved platypuses with UV light to see what would happen, and they obtained the same result, thus corroborating those from the Mammalia study. The Western Australian Museum team also found a selection of other mammals exhibited biofluorescence, including the common wombat (Vombatus ursinus).

The only other monotremes alive today are the echidnas or spiny anteaters, so once the biofluorescent ability of their platypus relative was discovered, they too were tested in the same way. What was duly discovered was that their long spines shone a bright gleaming white, as if they had been dipped in correction fluid. So too did the spines of hedgehogs and porcupines, even though these three types of spiny mammal are all only very distantly related to one another. This demonstrates that biofluorescence has evolved independently across the spectrum of mammalian taxonomic groups, rather than in just one or two closely related ones.