{{Infobox
| title = Platypus
| binomial = Ornithorhynchus anatinus
| order = Monotremata
| electroreceptors = about 40,000
| stomach = none
| sex chromosomes = 10
| glows under UV = yes
}}

'''The platypus''' (''Ornithorhynchus anatinus'') is a semiaquatic, egg-laying mammal endemic to eastern Australia and Tasmania, and the animal most often accused of being a forgery.

== Accused of being a hoax ==
When the first specimen reached Britain in 1799, the naturalist George Shaw examined the pelt for stitches, on the reasonable assumption that somebody had sewn a duck's bill onto a mole.<ref>George Shaw, ''The Naturalist's Miscellany'' vol. 10 (1799), plate 385.</ref> The cuts he made while checking are still visible on the specimen held at the Natural History Museum.

The platypus was not a fraud. It was, however, the strongest circumstantial evidence for fraud that anyone in London had ever been handed.

== Hunting with its eyes shut ==
A platypus closes its eyes, ears and nostrils underwater and hunts entirely by electroreception, using about 40,000 electroreceptors in its bill to detect the electrical fields of muscle contractions in shrimp and insect larvae, cross-referenced against mechanoreceptors that sense the pressure wave from the same movement.<ref name="pettigrew">John D. Pettigrew, "Electroreception in monotremes", ''Journal of Experimental Biology'' 202 (1999), pp. 1447-1454.</ref> The delay between the two signals gives the distance, so the animal is effectively echolocating with somebody else's twitching.<ref name="pettigrew" />

It has no stomach: the oesophagus connects more or less directly to the intestine, a trait shared with about a quarter of fish species and almost nothing else with fur.<ref>Jaime Castro et al., "Recurrent gene loss correlates with the evolution of stomach phenotypes in gnathostome history", ''Proceedings of the Royal Society B'' 281 (2014).</ref>

== Venom ==
Males carry a spur on each hind leg connected to a venom gland, which becomes most active in the breeding season. The venom is not lethal to humans but produces pain that does not respond well to morphine and can last for weeks or months.<ref>P. J. de Plater et al., "The venom of the platypus", ''Toxicon'' 33:2 (1995), pp. 157-169.</ref> It is one of very few venomous mammals, and the only one whose venom delivery is seasonal, on the hind foot, and reserved mainly for fighting other males.

== Other features that sound invented ==
* Lays eggs, then feeds the young on milk that seeps through the skin, as it has no nipples.<ref>Frank Grutzner et al., "In the platypus a meiotic chain of ten sex chromosomes shares genes with the bird Z and mammal X chromosomes", ''Nature'' 432 (2004), pp. 913-917.</ref>
* Has ten sex chromosomes arranged in a chain at meiosis, some of which resemble bird chromosomes more than mammalian ones.<ref>Grutzner et al. (2004).</ref>
* Fluoresces blue-green under ultraviolet light, for reasons nobody has established.<ref>Paula Spaeth Anich et al., "Biofluorescence in the platypus", ''Mammalia'' 85:2 (2021), pp. 179-181.</ref>

The genome was sequenced in 2008 and contains a working mixture of reptilian, avian and mammalian genes.<ref>Wesley C. Warren et al., "Genome analysis of the platypus reveals unique signatures of evolution", ''Nature'' 453 (2008), pp. 175-183.</ref> The platypus is not a mistake or a committee decision; it is a lineage that split from ours roughly 187 million years ago and kept the features we discarded. We are the ones who dropped electroreception.

== See also ==
* [[Wombat]]
* [[Mantis shrimp]]

== References ==
{{reflist}}

[[Category:Animals]]
[[Category:True but improbable]]