Colours of Wildlife - The Platypus
Created | Updated May 26, 2013
The Platypus
Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"
This time I have for you a crittur that is not South African: the Platypus, Ornithorhynchus anatinus. This one, in case any of you did not know, comes from our fellow southern-hemisphere country, Australia. It is sometimes called a duck-billed platypus, although there aren’t any other kinds of platypus – it is the only species.
This can’t possibly exist
When platypuses (platypi/platypodes) were first witnessed and described by Australian settlers and a pelt and sketches were sent to Britain, scientists were skeptical. The skin seemed to be several different animals patched together, with the bill of a duck added in front. George Shaw, the scientist who first described the species, had to check the skin carefully for stitches. But science soon had to concede that this little thing was indeed real. Not only westerners acknowledged the weirdness – even Aborigenes said, in one story, that it was a hybrid between a water rat and a duck and, in another,that when the animals were created and divided into groups, the platypus decided to rebel, refusing to conform to any group. Its funny outward appearance turned out to be the least of it; the various strangenesses of the platypus were only beginning to be revealed.
A Venomous Mammal?
Venom is not associated with mammals. We think of snakes, of stinging invertebrates, of jellyfish, but usually not of fluffy warm-blooded beasties being venomous. Yet, the platypus has a sting! It is in the form of a spur on its hind legs, supplied by venom glands in its thighs. Platypus venom can kill animals up to the size of a dog, but in humans it ‘merely’ produces horrifyingly excruciating pain that does not respond to painkillers. Victims can remain hyper-sensitive to pain for months afterwards. Today we know a few other kinds of mammals that have venom: shrews, solenodons (large shrew-like mammals) and slow lorises (a kind of primate), all of which have venomous bites or saliva. But this is still a very small group amongst which the platypus stands out for the power of its venom and its unique method of delivery.
An Egg-laying Mammal?!
But another aspect of the platypus is even more radical. In fact scientists argued about it: for almost a century after its initial discovery, it was still not clear or fully accepted that it did, in fact, lay eggs. It was Scottish post-graduate student William Caldwell who in 1884, with the help of some Aborigines, found a female who had just laid an egg and also had a second egg in her uterus, thus proving beyond a doubt that this mammal did indeed lay eggs!
Platypus eggs are small (11 mm/0.43” in diameter) and have leathery rather than hard shells. They are incubated inside the uterus for 28 days before being laid. A clutch contains one to three eggs. The mother then incubates them for a further ten days, curling around them to warm them with her body. The blind, naked and helpless babies hatch, and then suckle from her for three to four months.
A Highly Unique Group
Platypuses are mammals – they have characteristic mammalian features like fur, milk-gland and warmbloodedness (although their body temperature, at 32 degrees Celsius/90 degrees Fahrenheit is slightly lower than that of most mammals) – but indeed their egg-laying and other features prove them to be very distinct. Today they are classified, along with the spiny anteaters or Echidnas (also of Australia and New Guinea), as Monotremes, meaning mammals with just a single genital/excretory opening, called a cloaca. In this and other features they resemble reptiles. Monotremes also don’t have well-developed external ears like other mammals, and they have reptile-like features of their skeletons. While as noted they do produce milk for their babies, they don’t have nipples. Instead, the milk oozes from the skin and the babies lick it up.
Amazing Adapted
This doesn’t mean that monotremes are ‘primitive’. Like everything that survives today, they have proven capable of surviving … they are well-adapted to their environments, and are continuing to evolve. Platypuses are quite successful in the streams they inhabit. Although they have low-ish body temperatures, they still maintain their inner body heat even in icy cold mountain streams. Their flat, webbed feet, from which their common name comes, are very useful for paddling around. Furthermore the webbing can be folded back to leave the toes clear when a platypus walks on land. This also allows them to use their claws to excavate their sleeping and breeding burrows in the riverbanks. Although often described as beaver-like, the tail of a platypus is not exactly similar, being furry rather than naked and rubbery like a beaver’s. The tail is used, along with the hind legs, for steering underwater and also as a storage organ for fat reserves. It is also used by a platypus mom to carry soft plant material for lining her nesting burrow. Platypus fur is soft, dense and waterproof. The eyes, ears and nostrils are shut tightly when the platypus is submerged. But how, then, does it perceive its environment while it is swimming? Well …
That Remarkable Bill
The ‘duck bill’ of the platypus is in fact a very sensitive organ, and perhaps the most remarkable thing about it. Unlike the hard bill of a duck, a platypus’s beak is soft and fleshy. In the skin it contains thousands of special receptors that first of all detect touch, which alerts it to the presence of tidbits as it probes the mud of stream bottoms. But more remarkably there are receptors that detect electricity! While we don’t often think about it, indeed we and all living creatures actually run on electricity. Our muscles and nerves constantly produce tiny electric fields by their activity. And platypuses can ‘see’ these electric fields with their bills! Working closely together with the touch receptors they send an ‘image’ to the brain mapping the environment the platypus is exploring. From the electric field intensities it can judge the direction and distance to worms, shrimps and other aquatic creepy-crawlies, and home in on them. It has to eat 20% of its bodyweight in such food items each day, and typically spends half of the day foraging. A platypus wiggles its head about all the time as it swims, to sweep these sensors on its bill through the water. Today we know other animals that are also electro-sensitive, such as hammerhead sharks and a few other species of fish. Some species of dolphin may also have this sense, but apart from them, no other mammal we know of.
Evolution of the Platypus
I frequently feature in Colours of Wildlife species that are representative of highly distinct lines of evolution. The Platypus is a sterling example. Along with the spiny anteaters or Echidnas (which I also hope to feature here soon) it has diverged from the evolution of all other mammals very long ago. I’ve seen it said that they might have diverged over 200 million years ago, which would put the divergence pretty much at the very start of mammalian evolution. Personally I am not quite sure about this. The oldest presently known fossil of a monotreme is about 120 million years old, from the Cretaceous period when dinosaurs were still flourishing. But this fossil, called Teinolophos, is already quite similar to the modern platypus (although tiny) so certainly there had already been a good period of monotreme evolution going on.
It is also not clear where monotremes first evolved. Today they’re known only from the Australian region, and their fossils also predominantly come from there. But if indeed they have diverged very long ago they must have been more widespread, since in those days the continents were still connected to each other. Indeed, a platypus-like fossil has been found in Argentina, showing that the monotremes must have been present in Gondwanaland (the ancient southern continent) prior to its break-up around 167 million years ago. It would be wonderful if more fossil material can be found to tell us more of this weird and fascinating group.
