At first glance, the platypus looks like a strange hybrid animal straight out of Greek mythology. When it was first described by zoologist George Shaw around 1800, many of his peers thought it was a prank. They even tested the original platypus specimen for stitching. It seemed that the animal was blurring the boundaries between different classifications when the science of taxonomy was still developing. We now know that this small semi-aquatic mammal, which can be found in the freshwater rivers and estuaries of eastern Australia and Tasmania, belongs to the order of animals called monotremes.
Apart from the platypus itself, there are only four other monotrem species left on the planet, all of which are echidnas (also known as spiny anteaters). They form a completely separate evolutionary lineage, different from placental mammals and marsupials, with which they last had a common ancestor about 166 million years ago. Fossils suggest that monotremes were once the dominant mammalian life in Australia and may have spread as far as South America.
The main turning point that caused their decline was probably the arrival of marsupials some 71 to 54 million years ago from mainland Asia. Marsupials had several advantages over monotremes and probably outnumbered them in terms of resources.
As a descendant of these surviving monotremes, the platypus is truly unlike any other animal on the planet. Its reproduction is a unique combination of mammalian and reptile characteristics. It has 10 different sex-determining chromosomes, unlike only two in humans and other mammals.
The potent venom that the male delivers through the sharp spurs located on the ankles contains chemicals mostly unique to the platypus. Even its beak only outwardly resembles a duck; in fact, it is filled with electrical sensors that allow it to move underwater even when it lacks vision.
Despite these eccentric characteristics resulting from its different evolutionary path, the platypus has all the traits of mammalian ancestors. In this article, we’ll look at six main characteristics that the platypus has in common with most other mammals. Some similarities are expected, but some may be surprising.
The platypus has mammary glands.
Perhaps the most important feature of mammals is the milk-producing mammary glands that female platypuses have to feed their young. The name “mammal” testifies to the importance of these glands in the classification and identification of the entire class of mammals. But the reproductive behavior of the platypus is much stranger than that. While all other groups of mammals still living on the planet give birth to live young, monotremes are distinguished by their ability to produce eggs instead. The very name monotreme means “one-time opening”. This refers to the only duct through which he urinates, defecates, and reproduces.
The first part of the reproductive process is like a reptile. After mating a pair of platypuses, the female produces several small leathery eggs, which spend about 28 days inside her body, and then incubate outside for another 10 days. The developing embryos feed on the yolk.
However, after the eggs have hatched, the mother will start giving milk to her cubs. Milk production is an interesting process. Since the female is missing any nipples, milk leaves the body through the skin pores in the abdomen. Interestingly, milk contains powerful antibiotics that protect babies from infection. This could have powerful applications for the future use of antibiotics in humans. The young are weaned three to four months after hatching from eggs and soon become independent. No other animal on the planet, except for echidnas, can reproduce and raise young in this way.
The platypus has fur
Mammals are the few animals on the planet that have real fur for isolation. The platypus is no exception. Both the body and the beaver tail of the platypus are covered with dense brown, waterproof fur (many thousands of hairs per square inch), which allows it to trap air and retain heat. The fur is so thick and luxurious that once in Australia, colonists hunted the platypus to make clothes. This practice continued until the Australian government granted the platypus official protection in the early 20th century.
Fur is also scientifically interesting. In 2020, researchers discovered that platypus fur actually glows an eerie blue-green light when exposed to an ultraviolet light. It does this by absorbing light during the day and then re-emitting it in a different color. While this is common in many furless animals, including reptiles, amphibians, fish and birds, it is relatively rare in mammals (although scientists are finding more and more exceptions every year, including flying squirrels and Tasmanian devils). It’s unclear what purpose it serves – or if it serves any purpose at all – but it’s a fascinating phenomenon nonetheless.
Warm-bloodedness (also known by the scientific term endothermia) refers to the body’s ability to raise its body temperature above ambient temperature. Although not every mammal can perfectly regulate its body temperature in this way, it is still a common feature of most mammals. The platypus is no different in this respect; It metabolizes enough heat to keep you warm and comfortable even in cold water. However, it has a lower average body temperature, around 90 degrees Fahrenheit, as opposed to a body temperature of 99 degrees for most mammals. This could be an adaptation to life in harsher conditions.
The platypus has a four-chambered heart.
Mammals and birds are the only animals on the planet that have a four-chambered heart; fish have only two chambers, while amphibians and reptiles have only three. The four-chambered heart has a huge advantage because it is able to separate the oxygen-rich blood leaving the lungs from the oxygen-poor blood entering the lungs. This more efficient circulatory system allows for more physical activity and fewer rest periods, supplying cells with generally richer oxygenated blood.
The platypus has the structure of a mammalian skeleton.
People, whales, elephants, and platypuses may look very different, but they all have similar skeletal structures. One of the most important features of the mammalian skeleton is the lower jaw; it consists of a single piece of bone that is attached directly to the skull. Instead, in most other vertebrates, the jaw consists of several parts. Mammals also have three small ear bones that transmit sound vibrations from the eardrum to the inner ear, where they are converted into nerve impulses. These ear bones are believed to have evolved from the lower jaw bones of earlier reptile ancestors.
These are all common features of the platypus. However, there are several key differences between the platypus and most mammals. In the platypus, the gait is more like a reptile because the legs are located on the side of the body, not under it. They also have extra bones in the shoulder that few other mammals have.
The platypus has sweat glands.
Mammals have glands on most or parts of the body. Although humans are one of the few animals that sweat to cool off, most mammals still use these glands for different purposes. As mentioned earlier, a female platypus literally sweats milk from her belly to feed her cubs. Scent labeling is another important use for these glands.
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