The

Puzzling Problem of the

Platypus

In 1798, an eminent zoologist at the British Museum named George Shaw received a dried and most unusual specimen from a newly-established colony in Australia. This unknown creature had many strange qualities about it: the flat tail of a beaver, the body and soft, fine fur of an otter or mole, and, most outlandish of all, the flat bill of a duck that seemed to fit quite awkwardly onto its furry head. In fact, it was so odd and so unlike anything else they had ever seen that the British scientists dismissed it as an elaborate hoax, ‘a high frolic practised on the scientific community by some colonial prankster’. They claimed that it was simply the end result of various animal body parts sewn together by some unscrupulous forger, and they weren’t best pleased with being sent such an obvious fake.

Their scepticism over the authenticity of this creature wasn’t unfounded. At the time, hoax animals were indeed being created from bits and pieces of dissimilar creatures and sold to gullible travellers, particularly in the Far East. One of the most notorious fakes was the ‘Feejee Mermaid’, an ugly, withered creature that people could fabricate by sewing the top half of a monkey or ape onto the lower half of a large fish.

So, with more and more bizarre and highly questionable specimens popping up from around the world, it’s unsurprising that George Shaw was wary about accepting this new Australian curiosity as the real deal. But upon thoroughly searching the specimen for signs of fakery and finding no stitches whatsoever, he was forced to admit that this animal – whatever it might be, and however improbable its mismatched body parts seemed – was indeed a genuine one.

Shaw gave the animal a name: Platypus anatinus. The word ‘platypus’ is derived from Greek words and means ‘flat-footed’ – a rather dull designation when one considers the animal’s many extraordinary features that might inspire a more vivid name (anatinus, Latin for ‘duck-like’, does at least reference its strange bill). In any case, Platypus turned out to be invalid for it had already been used as the name for a genus of wood-boring beetles, and the rules of nomenclature do not allow duplicates. A year later, Professor Johaan Blumenbach of Germany studied another specimen and gave it the name Ornithorhynchus, or ‘bird snout’. That is still the animal’s scientific name today, while platypus has become its common name instead.

The Egg-Laying Anomaly

Even though the scientific establishment now conceded that the platypus was a real animal, it took another 30 years before they accepted it was a mammal. True, it had fur – a unique and defining mammalian characteristic – but, unlike most mammals, the platypus had a single, all-purpose rear vent, a cloaca, like that of a bird or reptile, through which it does all its defecating, urinating, mating and birthing. To further complicate matters, no one could find those all-important mammary glands – and in any case, some scientists thought that an animal with a large, flat bill couldn’t possibly suckle.

In time, some of the mysteries of the platypus were solved. When specimens of baby platypuses reached Europe, scientists realised that they would have no difficulty in suckling because they hadn’t yet developed the bill that would otherwise have made it very awkward [1]. But it hardly mattered anyway because it was also discovered that female platypuses do not possess nipples; they simply ooze thick milk from modified pores in their skin, which the young suck from tufts of hair on their mother’s underbelly.

But one thing truly puzzled the experts. Dissections revealed that females sometimes had shelled eggs in their oviducts, although whether these were laid before they hatched or whether they hatched internally so that the young were born unshelled, nobody knew. The consensus at the time was that mammals did not – and could not – lay eggs. Even when some small, spherical eggs were found in a burrow beside an Australian riverbank that was inhabited by a platypus, many naturalists speculated that another animal, perhaps a reptile, had snuck into the platypus’s burrow and deposited them there. The native Aboriginal people insisted that the eggs did indeed belong to the platypus, but the Europeans dismissed their claims as absurd, and the argument raged for nearly a century.

The debate was only solved in 1884, more than 80 years after the first platypus specimen had been examined by George Shaw. Scottish embryologist William Caldwell found a platypus nest and shot the female that inhabited it. He discovered not only an egg already inside the nest, but also, much more crucially, another that was on the verge of being extruded from the female’s cloaca. Now there could be no doubt. Here was a mammal that did indeed lay eggs.

The Primitive Platypus?

We now know that the platypus sits (along with that other egg-laying mammal, the echidna) in the monotreme order (from the Greek monos, ‘single’ and trema, ‘hole’, in reference to its cloaca). One man, John Price, saw the platypus in 1880 and was clearly unimpressed; he described it as ‘helpless, deformed and monstrous.’ But he was wrong – the platypus is a highly adapted, specialised creature.

Take that characteristic duck-like bill, for instance. Unlike the hard beak of a real duck, the platypus’s bill is soft, rubbery, and very sensitive. The platypus lives in and around the rivers of eastern Australia and is an excellent swimmer, paddling with its webbed forefeet and steering with its hind. But since it closes its eyes and ears when it dives underwater, it becomes temporarily blind and deaf and must use another sense to find its food: electroreception. Although this ‘sixth sense’ is used by many species of fish (including the electric eel, which we’ve already explored), within the mammalian world it is possessed only by the monotremes (and possibly a few dolphin species; the jury is out on that).

The extraordinary snout of the platypus, which is covered with up to 40,000 electro-sensitive receptors, is swept from side to side like an underwater metal detector, picking up the minute, almost imperceptible, electrical impulses generated by muscular contractions of its prey, even if they are buried under silt. This sophisticated system allows the platypus to determine the distance and direction of potential prey and creates a vivid three-dimensional picture of its underwater world. In fact, far more of the platypus’s brain is devoted to the bill than to the eyes, ears, nose, tongue and rest of the skin combined, highlighting how important this sense is to the animal.

Worms, aquatic insects and small shrimps that are caught are stored in the animal’s cheek pouches until it surfaces a minute or so later. Then it mashes them up, not with teeth – for, like the echidna, it has none – but with horny, grinding plates on its tongue and palate. Strangely, the platypus also doesn’t have a stomach – its oesophagus connects directly to its intestines. Why evolution has eliminated the platypus’s stomach remains unclear, although it may be because a diet of soft invertebrates doesn’t require much internal processing.

On land, the flaps between its toes fold away to allow the platypus to use its front claws for burrowing into the riverbank. It is, in fact, a superb and industrious digger, constructing tunnels in the bank that can be 30 metres long. This earned it the name ‘watermole’ among early British settlers in Australia. A mother platypus cannot carry her babies around with her in her groove-like pouch while swimming, so she leaves them in an underground nest chamber as she looks for food, often plugging the mouth of the burrow with soil to keep them safe while she is away.

The platypus shows us what early mammalian offshoots, having branched out from the reptile lineage, might have looked like some 200 million years ago. And, indeed, the platypus seems to have retained some of its ‘reptilian’ features: a single orifice for all its urogenital functions; a waddling, lizard-like gait; undefined mammary glands; and, of course, the ability to lay eggs. Its endothermy, or warm-bloodedness, also seems to be incompletely developed, for whereas nearly all mammals keep their bodies at temperatures between 36 and 39°C, the platypus has an average body temperature of only 32°C – and even then, it fluctuates wildly.

So at first glance, it seems as though the platypus is a primitive kind of creature, the likes of which were superseded by more ‘advanced’ mammals in other parts of the world. It might even be tempting to describe the platypus as a transitional species, halfway between reptile and mammal. But it is, unequivocally, a true mammal, and a remarkable one at that. Yes, it possesses a bizarre mix of characteristics that today we might call primitive and rudimentary, especially compared with the more conventional mammals seen in the rest of the world, but it has retained those ancient ancestral features throughout its long evolutionary history. Clearly, they have stood the test of time and are still useful today.

The platypus is an animal that breaks most of the established rules. But to call it an ancient mammalian prototype that was later abandoned in favour of more ‘mainstream’ mammals is hugely disparaging to the platypus. It’s not so much an evolutionary freak as it is a biological rebel. And for that, it should be applauded.

^{_{[1] There is no universally accepted plural form of ‘platypus’, although most scientists use platypuses and you will note that is what I also use. Platypi, though often colloquially used, is technically wrong because platypus comes from two Greek words, not Latin. The linguistically correct Greek plural for platypus is platypodes, though this is considered rather pedantic and usually avoided.}}