How much do you know about egg-laying mammals?

Animals are human’s best friends and are deeply loved by people in daily life. However, many people do not know much about egg-laying mammals because they are not common and are extremely rare as ancient species. They are mainly divided into two types: echidna and platypus. Both live in Australia in the southern hemisphere and still retain the characteristics of viviparous animals. Friends who are interested can learn more about them.

1. Egg-laying mammals

Oviparous mammals are ancient species that are special cases left over from the transitional period when oviparous animals evolved into viviparous animals. Although they are not viviparous, these animals have innate mammalian behavior, body fur... and a series of characteristics of viviparous animals, so they still belong to mammals.

2. Types of Oviparous Mammals

There are two species, both living in Australia.

1. Tachyglossidae

The echidna family consists of two genera and two species, namely Tachygolssus aculeatus (or short-beaked echidna) and Zaglossus bruijnii (or long-beaked echidna). Echidna, also known as the spiny anteater, has hair and spines on its body, a long beak, feeds on termites and is good at digging. Although echidnas are oviparous monotremes, they also have a pouch. The eggs are laid directly in the pouch for incubation, and after hatching, the young continue to live in the pouch for a period of time. The short-beaked echidna is the most widespread and common extant monotreme, found across mainland Australia, Tasmania, and central and southern New Guinea. The short-beaked echidna of Tasmania is hairier and was once considered a separate species. The long-beaked echidna is now confined to the island of New Guinea, but was found on the Australian mainland and Tasmania during the Pleistocene. The long-beaked echidna is almost twice the size of the short-beaked echidna and is the largest member of the monotreme order. It has a long, curved beak, short, sparse spines, and relatively abundant hair. The long-nosed echidna was previously divided into three distinct species, with the three-toed echidna being widespread across the island and the other two species being confined to the highlands in the northeast. Long-nosed echidnas are now classified as a single species, with different subspecies.

2. Ornithorhynchus

Also known as duck otter, English name Platypus duckbill, Duckmole;

The most primitive and peculiar animal among living mammals. It is only distributed between Cape York in eastern Australia and South Australia, and also lives in Tasmania.

The most peculiar of Australia's monotremes is the platypus. The so-called monotremes are animals that are between reptiles and mammals. Although it is more advanced than reptiles, it has not yet evolved into mammals. The similarities between the two are that they both breathe with lungs, have hair on their bodies, and are warm-blooded; and monotremes reproduce by laying eggs, thus retaining important characteristics of reptiles.

Everyone who has seen a platypus says it looks really weird. When British immigrants first arrived in Australia and discovered the platypus, they exclaimed it was an "incredible animal." The platypus is about 40 cm long and is covered with soft, dense, short brown hair. Its skull is smaller than that of the echidna, and its brain is hemispherical, smooth and without convolutions. The limbs are very short, with five hooked toes and thin webbed feet between the toes, which resemble duck feet. When walking or digging, the webbed feet are folded in the opposite direction to the palm. The snout is flat, shaped like a duck's beak, with wide keratin gums but no teeth. The tail is large and flat, accounting for 1/4 of the body length, and acts as a rudder when swimming in the water.

The male platypus has a thorn on its hind foot that contains venom that can hurt people when sprayed out. It is almost the same as snake venom. If a person is stung by the thorn, it will cause severe pain and may take several months to recover. This is its "amulet". The platypus is an amphibious animal that usually lives in burrows near water. When in water, its eyes, ears, and nose are tightly closed, and it relies solely on perception to use its flat, soft "duck bill" to forage for shellfish. It has a large appetite and consumes food equal to its own body weight every day.

Although the mother also secretes milk to feed the young, they are not viviparous but oviparous. That is, the mother lays eggs, which are incubated by the mother's body temperature like birds. The mother has no breasts or nipples, and secretes milk on both sides of her abdomen. The cubs lie on her abdomen and lick it.

The larvae have teeth, but the adult gums have no teeth, instead they are replaced by continuously growing keratin plates. The front occlusal surface of the plate forms many raised transverse ridges, which are used to crush the shells of mollusks such as molluscs and snails, or to chop up other foods. The rear keratin plate is flat, and the flat uvula opposite the plate has an auxiliary "chewing" function.

Platypuses chase and mate in the water, and their eggs are shaped like turtle eggs. After the platypus baby hatches, it relies on breast milk for 4 months before it can go out to find food on its own. The platypus has a reversed biological clock; it sleeps during the day and is active at night.

The platypus can swim underwater and often builds its nest in swamps or on the banks of rivers with the entrance of its cave underwater, including mountain streams, stagnant or dirty rivers, lakes and ponds. It digs holes on the shore as shelter, and the holes communicate with the adjacent water. It is a bottom feeder, diving to the bottom of the water for feeding, with each dive lasting about a minute, using its mouth to explore the mud for shellfish, worms and small crustaceans, as well as insect larvae and a variety of other animal food and some plants. The platypus is distributed in southern Australia and Tasmania. It is the most primitive mammal in existence and an evolutionary link in the formation of higher mammals. It has great scientific research value in animal evolution.