Answers to last issue's Animal Do You Know?
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This one is about the very strange and fascinating platypus! The Platypus is one of Australia’s most extraordinary animals. The Platypus lives both on land and in water. It is approximately 50 cm in length and is covered in waterproof fur except on its feet and bill. The Platypus has dark brown fur on its back with light brown fur underneath. Its body is streamlined, and along with short limbs and broad webbed feet, it is perfectly built for swimming. Each of its feet has five clawed digits.
Platypuses’ back legs act as a rudder when swimming to help steer and change direction. The front feet have enlarged webbing that extends beyond the claws to provide power while swimming. So, despite its odd looks, the platypus is perfectly adapted to its
environment.
It has a bill and webbed feet like a duck, but is covered in thick fur like an otter, and has a flattened tail like a beaver! In fact, Platypus means "flat footed duck".
Classification of the platypus was initially a challenge as the number of specimens available in Europe were either incomplete or preserved. In fact, many scientists thought that the animal sent to them was a hoax.
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1. Is a platypus a mammal or a bird?
Ans: The platypus is a unique mammal, not a bird. Although it lays eggs, has a beak, and possesses webbed feet, it is classified as a mammal because it has fur, is warm-blooded, and produces milk to feed its young.
To remind you: 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. But platypuses are mammals that lay eggs! Even scientists were initially confused!
The platypus was ultimately placed into a new order called Monotremata. Monotremes are egg-laying mammals that produce milk for their young. They are found only in eastern Australia.
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.
Sequencing of the platypus genome (DNA) reveals that the platypus has about 18,000 genes; humans, by comparison, have somewhere around 20,000. Moreover, roughly 82% of the platypus's genes are shared between monotremes, marsupials (which carry their under-developed young in pouches like kangaroos), eutherians (mammals with placenta such as elephants and humans), birds, and reptiles. The overlapping features has led scientists to consider that the platypus actually represents a living missing link between reptiles and mammals.


2. Does a platypus have a stomach?
Ans: No, platypuses do not have a functional stomach. Their esophagus connects directly to their intestines, meaning they lack the acid-producing organ found in most mammals. Food is crushed by grinding plates in their bill, and digestion is completed in the intestines.
Platypuses have lost the genes for producing stomach acid and pepsinogen (protein-digesting enzymes). Because they eat small aquatic invertebrates containing calcium carbonate (which neutralizes acid), a stomach is not needed. 
Their digestive tract is simplified to skip the acidic stomach phase.

3. How does a platypus defend itself?
Ans: Male platypuses have a 1.5-2 cm long spur on each hind leg at the ankle connected to a crural gland that produces secretions. They are normally shy creatures. When threatened, they hook these spurs into predators or rival males to inject a complex, highly painful venom, causing immediate, severe pain and swelling.
While not fatal to humans, the venom is strong enough to kill smaller animals like dogs. It is most potent during the breeding season to establish territory.
Platypuses are shy and cautious. They prefer to avoid danger by diving underwater and hiding in their riverbank burrows. They use their strong claws mainly for digging. Only males are venomous; females lack functional spurs.

4. How does a platypus find its way in water?
Ans: Platypuses have eyes above their bill so they are not able see things directly below them. Skin flaps cover the Platypus’ eyes, ears and nostrils underwater which means it is temporarily blind when swimming. Instead, the Platypus uses its bill to feel its way and find food under water.
The Platypus’ diet consists of a variety of insect larvae, yabbies, small fish and worms. Platypuses find their food amongst the rocks, leaf litter and other material on the bottom of the water body with their bill. They then store the food collected in large cheek pouches, and chew it when they reach the surface. Each dive usually lasts between 30 and 60 seconds.
Since platypuses essentially turn off their sight, smell, and hearing under water, how do they hunt for prey? They rely instead on a highly sensitive bill to detect prey in two ways:
. they use specialised electro-receptors to detect tiny electric fields from prey and
. use mechanoreceptors to sense water pressure and movement.
This allows them to navigate and hunt even in dark, murky water where sight will be useless.
Electrolocation: The bill contains over 40,000 electroreceptors that detect weak electric currents produced by the muscle contractions of prey, such as shrimp and worms.
Pressure Sensors (Mechanoreception): Along with electroreceptors, the bill has over 60,000 mechanoreceptors, known as "push rods," which are sensitive to touch and water pressure, allowing them to detect movement in the water.
The platypus sweeps its bill side-to-side on the riverbed, using these sensors
to locate prey and navigate.

5. What is so special about platypus fur?
Ans: Platypus fur is exceptionally dense and specialized, providing superior insulation and waterproofing to keep the animal warm and dry in cold water. It consists of two layers: a waterproof topcoat of coarse guard hairs and a dense fine underfur that traps air. Platypuses use their fur to trap a layer of air next to their skin so they can remain buoyant and dry when they’re underwater, which they are a lot. The platypus spends about 12 hours every day underwater looking for food.
Recent research shows that it is biofluorescent, so it glows cyan/green under UV light! The reason for this is not clear but it may have something to do with night-time camouflage.
The fur is among the densest of all mammals. It acts like a wetsuit, keeping the skin dry and maintaining insulation, which is better than that of polar bears or beavers.
A groundbreaking discovery this year showed that platypuses are the first known mammals with hollow pigment-containing structures (melanosomes) in their fur. That is, it possesses unique hollow pigment structures similar to bird feathers. Such a feature was previously thought to only exist in bird feathers.
The platypus uses its hind claws for constant, meticulous grooming to keep the fur in top condition. This unique combination of features makes the platypus one of the most remarkable and specialized aquatic mammals.

Sources: Several, including 
https://wwf.org.au/blogs/9-interesting-platypus-facts/