Discussion

The Strangest Mammal

When in 1788 or 1789, the first pelt of a platypus arrived in England from Australia, it was initially thought to be a hoax. It seemed to be an impossible mixture of parts from other animals; a duck's bill, an otter's fur, webbed feet, and a beaver-like tail. It didn't help that at that time it was a fad among taxidermists to craft fake "mermaids" and other composite monster curiosities for sale to collectors.

This is a sketch of one such hoax, the so-called Feejee Mermaid that was shown by P. T. Barnham in his New York museum in 1842. It was made from a monkey's head and arms sewn onto a fish's body.

It took an extremely minute examination to convince experts that the platypus was a real animal. The scientific name of Platypus anatinus was promptly assigned to it, but rules of precedence overruled that. The Platypus genus name had already been assigned to a group of beetles. The scientific name for platypus was changed to Ornithorhynchus anatinus. It took some time before biologists learned just how unusual the platypus really is.

It took decades of debate for biologists to finally agree that, unlike almost all mammals, Platypuses lay eggs instead of giving live birth. It isn't the only mammal to do so. The platypus is a member of a mammal subgroup called Monotremes, all of whom lay eggs.

Platypuses are only found in eastern Australia and on the island of Tasmania. Fully grown platypuses range from 15 to 25 inches in length. Males are a little larger than females. The largest ones are found on Tasmania.

As one would normally expect, there are two platypus genders; male and female. The standard among mammals is that there are two sex chromosomes. Females have two X chromosomes, and males have an X chromosome and a Y chromosome pair. Platypuses are different. They have ten sex chromosomes. Females end up with five X chromosome pairs, and males have five XY chromosome pairs. If there are not precisely 5 of the appropriate pairs, the chromosomal imbalance is usually fatal or severely harmful to the embryo.

The platypus mating season varies somewhat by location, but it generally occurs from late July through October. After mating but before laying eggs, female platypuses weave spherical, cup-shaped nests in underground burrows using a variety of vegetative material. Two to four weeks after mating occurs, females lay one to three eggs; two are most typical.

The eggs do not have a hard shell. Instead, they have a soft, leathery, parchment-like shell similar to reptile or lizard eggs. Though the photo doesn't show it, the female incubates the eggs by wrapping her tail around them and by pressing the eggs against her stomach. Puggles (baby platypuses) "hatch" in 10 or 11 days. They are about the size of a jelly bean (the larger type) when they hatch.

The mothers have mammary glands but no teats. Milk is secreted through special ducts, much like sweat is secreted through pores. Puggles nurse by licking the milk from the mother's skin. Puggles nurse for three to four months before they are mature enough to forage on their own. Once nursing ends, platypuses leave the nest, hunt for food instinctively, and generally avoid others of their kind outside of mating season.

Platypuses are nocturnal aquatic animals who can stay submerged for at least two minutes before needing to surface for air. Their webbed feet and streamlined shape enable them to swim swiftly. Their rear feet and flat tail are used for steering.

Their fur is so thick that it is essentially waterproof, great for insulation in frigid waters. They have from 600 to 900 hairs per square millimeter depending on the source. Though platypus fur is compared to otter fur, otter fur is actually twice as dense.

Platypuses have an undercoat of hairs with a wooly texture and an outer coat of coarser guard hairs. Tiny structures called melanosomes in the cells of the guard hairs are hollow. Birds' feathers are the only other place hollow melanosomes are found. An extremely rare characteristic among mammals is that platypus fur is biofluorescent. It glows under ultraviolet light. This was just discovered in 2020. Biofluorescence is discussed further below.

The platypus "bill" resembles a duck bill, something which has led some to call them duck-billed platypuses. The bill isn't hard like a duck bill, however. It is flexible, spongy, and fleshy. Platypuses have no teeth. Instead, they have rough pads in the back of their jaws made of keratin, the same stuff that hair and horns are made from. The pads are used to tenderize food, sometimes with the help of stones which they spit out afterward. Food is often stored in cheek pouches before being further chewed and swallowed. Platypuses have no stomachs. Their esophagus leads to their small intestines where digestion occurs. Instead of having separate orifices for solid waste, urine, and reproduction, there is a single shared orifice called a cloaca like reptiles have.

The platypus diet consists mainly of insect larvae and nymphs, freshwater shrimps, worms and snails, small fish, fish eggs, and sometimes tadpoles.

Generally, when swimming under water and hunting for food, platypuses swim with their nostrils, eyes, and ears tightly closed, which leads to the question, how do they find their way around and find food? Quite well, actually. When the muscles of all living creatures contract, platypus prey included, a faint electrical field is generated. Platypus bills have over 40,000 of what are called electroreceptors that enable them to detect those fields from as much as a foot away. Timing differences from when different sensors detect the fields tell the platypus where to find the prey. Few other creatures have those receptors.

The bills also have a large number of mechanoreceptors; pressure detectors. They tell platypuses what the physical environment around where they are swimming is like. They can function quite well in murky water without being able to see with their eyes.

As can be seen in the photo above and the one below, platypuses have five toes on each of their feet. Their front feet have webbing that extends beyond their toes. It can be retracted for protection on land and for giving their claws purchase for walking and digging. Webbing on their rear feet does not extend beyond their toes.

In addition, adult male platypuses have hollow spurs on the backs of their rear feet that are filled with venom produced in glands in their thighs. The spur normally lies flat against their limb but is raised when needed.

Australia

The platypus is part of Australia's culture and has been for tens of thousands of years. Aboriginal peoples hunted the platypus for food and prized its thick tail which is rich in fats. The animal is featured in many Aboriginal creation stories and was seen as the offspring of a duck and a water rat. It was recognized as an extraordinary creature that defied strict categorization. The platypus symbolizes balance, adaptation, and the choice to stay true to one's identify rather than being claimed by a single group.

Modern Australia uses the platypus as a symbol of its identity. A platypus named Syd was the official mascot for the Sydney 2000 Olympic Games. It appears on Australian currency like this 1966 - 1984 20¢ coin.

It has often appeared on Australian postage stamps like this 1959 1-shilling stamp.

San Diego Zoo's Safari Park

The zoo's Safari Park in Escondido is the only place in the world outside of Australia where you can see a live platypus. It has one on exhibit in the Walkabout Australia section. There were originally two, a male and female pair, but the female died this past March at the ripe old age of 21. The male is about 15 years old. Because platypuses are nocturnal, the exhibit is kept darkened inside during the day so that the zoo's animal is active during humans' daylight hours. There is just enough light so that people can see well once their eyes adjust.

Biofluorescence and Bioluminescence

It was mentioned earlier that platypus fur is biofluorescent. Some confuse the difference between that and bioluminescence. Many people are familiar with fluorescence from displays of invisible ultraviolet light being shown on some kinds of mineral in a dark room. The rocks become lit up with vivid colors that are not apparent under normal light. The photo below shows an example of corundum being illuminated with ultraviolet light.

What happens is that the frequency of the invisible ultraviolet rays has been shifted to the visible spectrum when it is reflected off of the mineral. Biofluorescence is just fluorescence when the material being lit with ultraviolet light is organic, like, for example, platypus fur.

Bioluminescence is entirely different. It results from the production and emission of light by a living organism as a result of an internal chemical reaction. This midwater jelly illustrates the idea. The light comes entirely from the creature itself. It isn't a reflection. It can turn the light on or off at will. Fireflies provide another common example.