Apple #333: The Platypus

I cannot remember now how this came up, but it did. I was e-mailing a friend and I mentioned a platypus. There was a reason; I think I was making a joke, but I can't recall anything further than that. (No, it was not a dirty joke! Sheesh.)

But I wound up looking up information about the platypus. And there are so many strange facts about this animal, I just had to share them with you.


Print of the platypus, by John Gould, from 1863. Goofy-looking, aren't they?
(Image from Wikimedia Commons)


Nobody agrees what the plural should be.

• Most of the time, words that end in -us, as platypus does, are Latin words. Usually, to make the plural of these kinds of words is to change the -us to an -i. So lots of people think that the plural of platypus is platypi.

• Not so.

• Platypus is actually derived from Greek, not Latin. Specifically, it comes from πλατύς ("platys", flat, broad) and πους ("pous", foot), meaning "flat foot" (see the section below on webbed feet).

• So the plural of platypus technically should be platypodes. But who in the world ever says platypodes?

• Some people avoid this difficulty and go for platypuses. But that sounds really awkward, doesn't it?

It's an egg-laying mammal.

• For an animal to be a mammal, it must give birth to live young, that is, not in an egg the way a chicken or a fish does. But the platypus, a mammal, lays eggs.

• The platypus also has fur, is warm-blooded, feeds its young with milk produced in mammary glands, has a single bone in its lower jaw, and has three middle ear bones -- all the other characteristics required of mammals.

• (By the way, five species of mammals lay eggs. The platypus is one, and four species of echidnas make up the rest.)

It has a bill like a duck.

• But this duck bill is covered in a skin that some describe as leathery, others call rubbery.

• The nostrils are at the end of the bill, which allows the platypus to breathe even while swimming.

• But the platypus dives underwater a lot to look for food and dig its burrows, and the fact that its nostrils can be closed off comes in very handy.

Platypus, showing off its amazing bill
(Photo from The Complete Platypus)

• And this bill -- which really is not that much like a duck's -- is a sensory organ in and of itself. That's right,

It can sense electrical fields caused by muscular movements of its prey.

• In the skin of the bill are all sorts of receptor cells -- nerve endings, if you like. They can sense touch, like our skin does, hot and cold, etc.

• But there is also a row of a different kind of receptors -- about 850,000 of them -- that sense electrical impulses.

• Here's how it works. Say some little animal is trying to hide out in the sandy riverbottom and thinks it's being all sneaky, but then maybe it flinches or even moves slightly. When it does that, its muscles generate an electrical pulse which the platypus can sense with its super-sensitive bill, and then snap! the platypus catches the animal.

• (It doesn't eat what it's caught right away, but stores the food in cheek pouches. When the pouches get full, the platypus surfaces and crunches -- well, does not crunch since a platypus has no teeth, only grinding pads -- grinds up its food.)

• Scientists think that, when it is swaying its bill back and forth and rooting around in the sand, the platypus is using those electroreceptors to pick up electrical activity.

• In fact, this is probably how the animal "sees" underwater at all. Because while the platypus swims, its eyes and ears are shut.

Platypus swimming for the bottom, its eyes and ears shut
(Photo from The Complete Platypus)

• Only the platypus and a few species of fish have this electroreceptor ability.

It has webbed feet.

• The platypus lives in rivers, streams, and coastal lakes in Australia.

The green patch indicates where the platypuses live in Australia.
(Map from Unique Australian Animals)

• It has to eat 20%-25% of its body weight each day, and since it eats worms and crayfish and frogs and things like that that live in the water, the platypus spends a lot of time swimming around.

• So, webbed feet are definitely an asset.

• Even though its feet are webbed, the platypus doesn't rely on the webbing to make it go faster, but for steering. I'm not sure how the researchers know that, but that's what they say. I guess the platypus mainly kicks, sort of, to get around in the water.

It has a tail like a beaver's.

• The platypus uses its flat, paddle-like tail, not for propulsion, but as a rudder while swimming.

Here you can see how wide the platypus' tail is.
(Photo from a MySpace page called the Metaphysical Platypus)

• Like the beaver, the platypus also uses its tail to push soil around when digging burrows in the sides of riverbanks.

• The tail is also a great place to store fat. That extra fat comes in handy if the platypus has trouble finding food for a time, or if the platypus is a female and needs to incubate her eggs (more about the eggs below).

Its legs attach in a weird place.

• In other types of mammals, the legs attach underneath the body. That's true of your body, for example. That's also true of other mammals, like a dog or a horse or a cat: the legs extend down from below the body.

• In a platypus, though, the hips and shoulders attach on the side of the body. This is another characteristic, like egg-laying, that is more reptilian than mammalian.

See how the shoulder joint kind of sticks out sideways?
(Painting by Rod Scott, sourced from jameswatkins.com)


That's very similar to what this Italian wall lizard's shoulder joints are doing.
(Photo from Zooillogix)


It's venomous.

• The platypus has a long talon, called a spur, on the ankle of its hind legs. Actually, the spurs fall off the females after they're a year old, so in adult platypodes, only the males have ankle spurs.

Ankle spur on a male platypus
(Photo from Wikimedia Commons)

• These spur contains venom. It can kill small animals up to the size of a dog. Though the venom isn't strong enough to kill a human, it can cause you enough pain that you couldn't do much more than writhe around. And the venom can work itself into your immune system so that you feel pain at the slightest stimulus for a long, long time afterwards. The only other substance known to have this effect? Really strong opiates that people abuse for years.

• The males only produce this venom during the breeding season, and platypuses are shy and will probably run away from you, but even so. Watch out for them platypi!

It growls.

• Male or female, if a platypus doesn't like what you're doing and wants you to go away, it will growl. Apparently, the growl sounds like that of a puppy's.

The whole reproductive process is odd in many ways.

• Researchers have recently discovered that the platypus has 10 different sex chromosomes. Some of them are typical of mammals, some typical of birds.

• The female platypus has two ovaries, as most female mammals do, but only the left ovary actually works. This business of having a single working ovary is common in birds.

A platypus egg.
(Photo from Geneva Schools)

• After fertilization, the female incubates usually 2 eggs internally -- is pregnant with them, so to speak -- for about 28 days. Then she lays the eggs and keeps them warm externally for about 10 days.

• A chicken, by comparison, incubates internally for 1 day and externally for 21 days.

• While a chicken sits on her eggs, the platypus swims around with hers, the eggs curled up under the fattest, warmest part of her tail.

The word for "baby platypus?" Puggle, of course.


The female produces milk, but not through teats

• When a cat, or a pig, or a cow has babies, they line up to suck at their mother's teats to get the milk, right?

• When a platypus has babies -- or when the platypus eggs hatch -- they climb onto her abdomen.

• There, the mother's mammary glands produce milk, but the milk leaks out through the pores of her skin and collects in grooves. The young puggles lap up the milk from the grooves.

• When the mother is lactating, she has to consume 90% to 100% of her bodyweight in food each day.

(Photo from Curious Animals)

No wonder, when the first people from England saw drawings of the platypus, and even when they saw the actual animal itself, they thought it was a hoax.


Probably the reason the platypus seems so strange is that, as scientists now know, its genetic map is part bird, part reptile, and part mammal.


Diagram showing the various characteristics of the platypus and which general animal group's genes they come from.
(Diagram by Zina Deretsky of the National Science Foundation)


One scientist, Michael White, has a lot to say about this characterization of the platypus as 1/3 this and 1/3 that. He says, it's all platypus, and it's all mammal. He feels quite strongly about this too.

Who knew the platypus could arouse such passion?


Sources
The Complete Platypus
Unique Australian Animals, Platypus
Geneva, Ohio Area City Schools, The Duck-Billed Platypus
ABC Australia, Scribbly Gum, Platypus Spurred to Action, July 2004
Online Etymology Dictionary, platypus
Onelook, platypus
Wikipedia, Platypus
Discovery Channel News, "Study: Platypus Retains Bird Sex Link," and Platypus: Lots of Sex Chromosomes, October 25, 2004
Jeanna Bryner, "Scientists decode mixed-up platypus genome," MSNBC Live Science, May 12, 2008