Are Platypuses Mammals?

Few animals on earth are as intriguing and confusing as the platypus. There have been countless debates about the taxonomical status of these unique creatures since they were first discovered. Because they have fur, they were considered mammals. Given that they lay eggs rather than have live births, this was disputed. When it was discovered that the females do indeed produce milk to feed their young, they were once again classified as mammals. So are platypuses actually mammals?

This small semi-aquatic mammal can be found in the freshwater rivers and estuaries of eastern Australia and Tasmania. It belongs to an order of animals called monotremes. Despite some eccentric characteristics born from its different evolutionary path, the platypus bears all the hallmarks of mammalian ancestry. This article will explore the six major characteristics that the platypus shares in common with most other mammals. Some of the similarities are expected, but a few of them might be surprising.

The Platypus Has Mammary Glands

Perhaps the most important mammalian feature is the milk-producing mammary glands that the female platypuses possess. The name “mammal” is a testament to the importance of these glands in the classification and identification of the entire mammalian class. However, the reproductive behavior of the platypus is so much stranger than that. Whereas most other groups of mammals give birth to live young, the monotremes are distinguished by their ability to produce eggs instead. The name monotreme itself means “single opening.” This refers to the single duct through which it urinates, defecates, and reproduces.

The first part of the reproductive process is similar to a reptile. After a pair of platypuses mate, the female produces a few small, leathery eggs, which spend about 28 days inside of her body and then another 10 days being incubated externally. The developing embryos rely on the yolk for sustenance. After the eggs are finally hatched, the mother will begin producing milk for her young. Since the female lacks teats of any kind, the milk leaves the body through skin pores in the abdomen. The young are weaned three to four months after hatching from the eggs and become independent a short time later.

The Platypus Has Fur

Mammals are the few animals on the planet that possess true fur for insulation. The platypus is no exception. Both the body and the beaver-like tail of the platypus are covered in dense brown waterproof fur that enables it to trap air for insulation. The fur is so dense and luxurious that the platypus was once hunted by colonists in Australia to make clothing.

In 2020, researchers discovered that platypus fur actually glows with an eerie blue-green light when subjected to the glare of an ultraviolet lamp. It does this by absorbing light during the day and then emitting it in a different color. While this is a common phenomenon in many animals without fur, it’s relatively rare in mammals. However, scientists are finding more exceptions every year, including flying squirrels and Tasmanian devils. It’s not clear what purpose this serves — or if it serves any purpose at all — but it’s a fascinating phenomenon nonetheless.

The Platypus Is Warm-Blooded

Warm-bloodedness, also known by the scientific term of endothermy, refers to the ability of an organism to raise its body temperature above that of the surrounding environment. While not every mammal can perfectly regulate its body temperature in this manner, it is still a common feature of most mammals.

The platypus is no different in this respect. It produces enough heat via its metabolism to keep warm and comfortable even in cold waters. It does, however, have a lower average body temperature of about 90 degrees Fahrenheit, as opposed to the 99-degree body temperature of most mammals. This may be an adaptation to life in harsher environments.

The Platypus Has a Four-Chambered Heart

Mammals, birds, and crocodilians are the only animals on the planet that possess a four-chambered heart. Fish only have two chambers, while amphibians and other reptiles have three. The four-chambered heart has an enormous advantage with its ability to separate the oxygen-rich blood coming out of the lungs from the oxygen-poor blood traveling to the lungs. This more efficient circulatory system enables greater physical activity and fewer periods of rest by supplying the cells with more oxygen-rich blood.

The Platypus Has a Mammalian Skeletal Structure

Humans, whales, elephants, and platypuses may look vastly different, but they all share in common a similar skeletal structure. One of the most important features of the mammalian skeleton is the lower jawbone. It is composed of a single piece of bone that attaches directly to the skull. Mammals also have three small ear bones that transmit sound vibrations from the eardrum to the inner ear, where they’re transformed into neural impulses.

However, there are a few key differences between the platypus and most mammals. The platypus has a more reptile-like gait because the legs are located on the side of the body rather than underneath. They also have extra bones in the shoulder, which few other mammals possess.

The Platypus Possesses Sweat Glands

Mammals possess various types of glands, including sweat glands, sebaceous glands, and mammary glands. While humans are one of the few animals that sweat to cool down, most mammals still use these glands for different purposes. As mentioned earlier, the platypus female quite literally sweats milk from the abdomen to feed her young. Scent marking is also another important use of these glands.