The first skin sent to London in 1799 was suspected of being a hoax sewn together from other animals (1799)
George Shaw took scissors to the pelt looking for stitches before describing it
Science · Biology
Platypus
Described 1799
Biology — monotremes and electroreception
The platypus is a semi-aquatic Australian mammal so improbable that the first specimen sent to London in 1799 was suspected of being a fraud stitched together from parts of other animals. With the echidnas it makes up the monotremes, the only mammals that lay eggs, and the female suckles her young not from teats but from milk oozing onto patches of skin. The soft, rubbery bill is a sensory organ: hunting with its eyes, ears and nostrils shut, the animal finds prey entirely by pressure receptors and tens of thousands of electroreceptors that pick up the faint electrical fields of a twitching shrimp or worm. Males carry a venomous spur on each hind ankle, making it one of very few venomous mammals; the venom is not fatal to humans but causes agonising pain that morphine barely touches.
How to spot them
- ▸A duck-like bill, webbed feet and a beaver-like tail on an egg-laying mammal
- ▸The first specimen in London in 1799 was thought to be a taxidermist's hoax
- ▸Hunts with eyes, ears and nostrils closed, locating prey by electroreception
- ▸Males have a venomous spur on each hind ankle
- ▸With the echidnas, one of only five living species of monotreme
Key facts
One of only five living mammal species that lay eggs
The other four are echidnas; the eggs are leathery and about 17 mm across
The female has no nipples — milk seeps through the skin onto patches of fur for the young to lap
Monotreme milk is unusually rich in antimicrobial proteins
It hunts with eyes, ears and nostrils sealed shut, finding prey by the electric fields of their muscles
Thousands of electroreceptors and push-rod mechanoreceptors line the bill
The male's hind ankle carries a venomous spur fed by a modified sweat gland
The crural gland's venom is agonising but not lethal to humans; it peaks in the breeding season
It has ten sex chromosomes, and a genome carrying reptilian, bird-like and mammalian genes (2008)
Five X and five Y chromosomes that link together in a chain during meiosis
Its Greek name means 'bird-snout', and the specific epithet means 'duck-like'
Shaw's original genus name, meaning 'flat-foot', was already taken by a beetle
Key ideas
- Electroreception in mammals: the bill combines electroreceptors with pressure receptors, and the tiny lag between the electrical pulse from a prey animal and the slower water-borne pressure wave may let the platypus judge distance, like counting the seconds between lightning and thunder.
- Monotremes split from the line leading to marsupials and placentals well over 150 million years ago, which is why they keep egg-laying and a single cloacal opening — 'monotreme' means 'one hole' — alongside fur, milk and warm blood.
Quick-fire facts
- •Ornithorhynchus anatinus (Shaw, 1799); the only living species in the family Ornithorhynchidae
- •Order Monotremata, which also contains the four echidna species
- •Males are about 40–63 cm long and up to 3 kg; females are smaller; Tasmanian animals are the largest
- •It has no stomach: the oesophagus runs almost straight into the intestine, and it has no teeth as an adult, grinding food between horny pads with grit scooped from the streambed
- •Eggs are incubated for about ten days after a gestation of around three weeks; young suckle for three to four months
- •The bill carries pressure receptors and electroreceptors, commonly quoted as about 40,000 of the latter
- •It has ten sex chromosomes; the sex-determining system resembles a bird's Z/W arrangement more than the mammalian X/Y
- •It appears on the Australian 20-cent coin, and is the emblem of New South Wales
- •Its fur biofluoresces blue-green under ultraviolet light, reported in 2020
- •The English plural is platypuses; 'platypi' is a false Latin plural for a Greek-derived word
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Sources
- Australian Museum — Platypus
- Wesley C. Warren et al., Nature 453 (2008) — Genome analysis of the platypus reveals unique signatures of evolution