Monotremes: characteristics and examples

Monotremes appeared at least 110 million years ago , at the beginning of the Cretaceous . Since then, the evolutionary history of these animals has made them one of the most enigmatic living mammals that we can find today.

Belonging to the group of mammals , the monotremes (Prototheria subclass), share the same evolutionary origin with two other large groups: the marsupials (Metatheria subclass, such as kangaroos and weasels), and placentals (Eutheria subclass or mammals with placenta, largest group to which we human beings belong). In this way, both monotremes, marsupials and placental mammals that inhabited and / or continue to inhabit the Earth today, have a common ancestor from which they are all descendants.

In the next section we will see in detail what are the characteristics that make monotremes so distinctive and special.

Carriers of various reptilian characteristics, as well as birds and mammals, monotremes were a mystery to science when they were discovered and studies began to try to classify them within the different groups that we can find in nature. Finally, they were described as mammals, these being some of the main characteristics of the most surprising monotremes :

• Monotremes are the only mammals that hatch from eggs , therefore they are oviparous animals . Unlike placental mammals and marsupials, whose sex is determined by the presence of a pair of chromosomes, in monotremes 5 pairs of chromosomes are responsible for determining the sex of the individual. To add to the surprise, one of these pairs of chromosomes is very similar to the one that birds and reptiles present in their genetic process of sexual determination.
• The body temperature of this group of mammals is lower than that of the other two groups of mammals.
• This group of animals usually has a small number of offspring per year, usually one or two, and when they lay their eggs, they present a membranous covering that reminds of the calcification of the outer membranes of the eggs of reptiles and birds.
• The offspring of these extraordinary mammals are very small in size and are characterized by the presence of a single tooth on the tip of the snout, which they make use of to break the egg shell at birth (just as the offspring of birds and reptiles are accustomed to to do).
• At birth, the young are very underdeveloped , especially their hind limbs, something that undoubtedly differentiates them from the young of marsupials and placental mammals.
• Monotreme teeth are specialized in cutting and grinding food.
• The middle ear of these animals is typical of mammals.

To learn more, we recommend checking out these other articles on the Characteristics of Mammals and this List of Names of Animals that Lays Eggs .

Currently, only 4 species of monotreme live and all of them inhabit exclusively in Oceania.

Ornitorrinco (Ornithorhynchus anatinus)

Platypus inhabit eastern Australia and the island of Tasmania. Their bodies are hydrodynamic, adapted to their aquatic habits. They are about 40 centimeters long, their hands and feet have interdigital membranes and their snouts resemble those of ducks, which serve to easily catch the small freshwater invertebrates on which they feed.

Another of its most distinctive characteristics is the presence of dewclaws on both hind legs, which are communicated with poisonous glands. Both juvenile individuals and adult males are carriers of these poisonous spurs with a defensive function.

Short-nosed Echidna ( Tachyglossus aculeatus )

We can find them in New Guinea, Australia and Tasmania. They are animals of terrestrial habitat, between 50 and 75 centimeters in length. They are characterized by a body covered with spines, a bulging head and a short thin muzzle without teeth, but adapted to the intake of ants and termites, which constitute their food diet.

Western long- beaked echidna ( Zaglossus bruijni ) and eastern ( Zaglossus bartoni )

They inhabit exclusively in New Guinea, presenting terrestrial habitats. Like the species described above, the body of long-snouted echidnas appears covered with spines, their head is bulging and, on the other hand, their snouts are longer. Also the length of his body is somewhat greater, about 70-80 centimeters. They also do not have teeth and their diet is based on insect larvae, which they extract from the ground thanks to their strong claws that allow them to dig holes in the ground.

In both echidnas, unlike the platypus, the poisonous glands associated with the dewclaws on their hind legs lack functionality.

If you want to read more articles similar to Monotremas: characteristics and examples , we recommend that you enter our Wild Animals category .