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How big is a platypus?

Happy birthday to a guy who is always linked to unique animals! I still have an aardvark drawing from him circa 2004 hanging on my wall, but rather than an aardvark, today I am honoring him with his request of "something to do with a platypus"!

The platypus has been around for... who knows... a really long time. The platypus was ultimately placed into an order called Monotremata, alongside the four living species of echidna. Monotremes are, notably, egg-laying mammals that produce milk for their young.

To simply separate the orders, mammals are warm-blooded, give birth to live young and feed them milk. Birds are also warm-blooded but lay eggs, and reptiles are cold-blooded egg-layers that rely on the sun or another heat source to warm them up. The overlapping features has led some scientists to consider whether the platypus actually represents a missing link between reptiles and mammals. Amniotes are the common ancestor of all mammals, birds and reptiles. Mammals split from birds and reptiles around 315 million years ago. Monotremes are not direct relatives of birds and reptiles, but they are often considered the most basal of all mammals. They split from the line leading to placental mammals - which includes humans - around 166 million years ago. The platypus's overlapping characteristics with other classes are likely evolutionary leftovers.

When Europeans first encountered the odd-looking platypus, it became the center of scientific debate: was it real or just an elaborate hoax?  The platypus (Ornithorhynchus anatinus) has a puzzling array of features. Not only does it have that iconic duck bill, it lays eggs (like a bird or reptile) but feeds milk to its young (like a mammal).

George Shaw, keeper of the natural history collections at the British Museum (which were to later become the Natural History Museum), accepted the platypus as a real animal. In 1799 Shaw was the first to scientifically describe it, assigning it the species name Platypus anatinus, meaning flat-footed duck.

However, Platypus was already in use as the name of a genus of wood-boring ambrosia beetles. So in 1803 Johann Friedrich Blumenbach published another description of the animal under the name Ornithorhynchus paradoxus - 'paradoxical bird-snout'. The animal later became recognized as Ornithorhynchus anatinus, meaning bird-snouted flat-foot. This hybrid name was accepted in accordance with the rules of priority when classifying animals with scientific names.  

Despite its odd look, the platypus is perfectly adapted to its environment. It has a furry, otter-like body, a tail the same shape as a beaver's, and a mouth reminiscent of a duck's. In his 1802 book, An Account of the English Colony in New South Wales, Colonel David Collins wrote of the webbed and clawed feet that allowed the animal to swim and burrow with ease. The males also have a pair of venomous spurs on their hind feet, but they don't use them for traditional attack or defense.

He was also fascinated by the platypus's bill, noting, 'the most extraordinary circumstance observed in its structure was, it having instead of the mouth of an animal, the upper and lower mandibles of a duck.' Before this account, when a skin and illustration of the animal were first sent to Europe, some suspected the strange animal was a hoax - perhaps a taxidermy construction of a duck's bill attached to the body of a mole. A typical platypus is 15 inches (38 centimeters) from its head to the end of its rump. Its tail adds an additional 5 inches (13 cm) to the animal's length. An individual weighs about 3 lbs. (1.4 kg), though platypuses that live in colder climates are bigger than those living in warmer areas, according to the Australian Platypus ConservatoryScientists have found fossils that suggest that ancient platypuses where twice as large as the modern variety, at 3.3 feet (1 meter) long.

Platypuses have dense, thick fur that helps them stay warm underwater. Most of the fur is dark brown, except for a patch of lighter fur near each eye, and lighter-colored fur on the underside.

Their front feet have extra skin that acts like a paddle when the animals are swimming. When platypuses are on land, their webbing retracts, making the claws more pronounced. The animals walk awkwardly on their knuckles to protect the webbing.

The bill of a platypus, sometimes called a duck-billed platypus, has a smooth texture that feels like suede. It is also flexible and rubbery. The skin of the bill holds thousands of receptors that help the platypus navigate underwater and detect movement of potential food, such as shrimp.

During courtship, female and male platypuses engage in a dance, during which the male holds the tail of the female with his bill, and the female leads them both through a series of slow circles, twists, and turns on the surface of the water, followed by mating. In captivity, reproductive behavior is controlled by the female. After mating the female platypuses construct a nesting burrow where they lay one to three eggs (about 1/2" in diameter and just slightly longer than 1/2"), which they incubate about 10 days before the young hatch. Hatchlings are just over 1/2" long with no fur, and are suckled for 120–140 days, at least based on observations in captivity.

Modern platypuses are endemic to eastern mainland Australia, Tasmania, and adjacent King Island, with a small introduced population on Kangaroo Island, South Australia, and are widely distributed in permanent river systems from tropical to alpine environments.

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