In the zoo, there is a small and delicate monkey, no larger than a fist, leaping around agilely in a tiny cage. Have you ever wondered why they are so small? These tiny monkeys are known as marmosets and they originate from South America.

If you have watched the movie "Rio", you may remember the mischievous gang of monkey thieves who used stolen gold watches as belts to pose as tycoons. This scene vividly depicts the size of the marmosets.

Their natural habitat lies in the forests of northeastern Brazil. Due to factors such as human intervention, they have also been introduced to cities in southeastern Brazil, including Rio de Janeiro, where they have become an invasive species.

Consequently, they were portrayed as mischievous thieves in the movie.

One distinctive feature of this group of small monkeys is the cotton-like tuft of white fluff above each ear, which gives them the name "cotton-eared velvet monkeys".

In terms of biological classification, there are dozens of marmoset species, with the common marmoset, also known as the cotton-eared marmoset, being the most prevalent.

Among the known marmosets are golden lion tamarins, royal tamarins, top tamarins, pygmy tamarins, black and white tamarins, and common tamarins, totaling 35 species across 3 genera.

The largest marmoset species, the golden lion tamarin, measures no more than 20 cm in length and weighs nearly 600 grams, slightly larger than a macaque cub.

On the other end of the spectrum is the pygmy marmoset, also known as the bonnet marmoset, which is about the size of a mouse, with a body length of approximately 15 cm and an average weight of 120 grams.

A newborn marmoset cub weighs less than 20 grams, similar in length to an adult's finger, and only reaches a weight of about 30 grams. Consequently, it can climb on people's fingers, earning it the nickname "thumb monkey".

The marmoset's body shape resembles that of a squirrel, with bead-like eyes, large ears, and a long tail.

Even their sleeping posture resembles that of a squirrel, as they either hide in hollow tree holes or huddle together on a branch, clinging to the trunk with their limbs and pressing their abdomens against the branch.

Feature One: A keen sense of smell

Marmosets possess a highly sensitive sense of smell. They rely on it not only to locate food and determine its ripeness but also to alert them to potential intruders and natural predators.

Marmosets use scent marking and communication, such as delineating their territory with urine or leaving scent messages for other marmosets to recognize.

Feature Two: Rich facial features

Facial expressions in marmosets are mainly conveyed through lip movements, while emotions are expressed through a combination of eyelid movements, ear positions, head fuzz, and whiskers.

Marmoset faces are easily recognizable, with some species having white "beards" (even females of the royal tamarin have long beards) and others sporting dense hair in shades of gray, brown, or golden.

Feature Three: Love for singing

Although tiny and difficult to spot in dense rainforests, marmosets often reveal themselves through their melodious voices. In marmoset colonies, females are more inclined to "sing", emitting intermittent high-pitched tones from time to time.

Feature Four: Versatility

Marmosets were initially domesticated by indigenous people who utilized them to catch lice from their hair. In the 18th century, they were brought to Europe and became pets of the aristocracy.