To find today’s animal I just flipped through my Encylcopedia of Mammals until I found something that looked cool. This strategy never fails me – there are just way too many cool animals out there. So today’s animal is the somewhat funny-looking monkey, Geoffroy’s marmoset.

This species is found in Brazil, in a small area in the southeast of the country. They live in the rainforest, hanging out at elevations of 500 to 800m. In one area, a hybrid population exists between Geoffroy’s marmoset and the black-pencilled marmoset. Apparently no one informed these monkeys that they’re different species, and thus shouldn’t mate. Naughty monkeys.

A Geoffroy’s marmoset, looking quite ponderous. Image By Brian.gratwicke at English Wikipedia. – Transferred from en.wikipedia to Commons., CC BY 2.5

Geoffroy’s marmoset is quite small; they are only about 20 cm in length, with a tail length of almost 30 cm. They are dark brown or black, with white foreheads, cheeks and throats. They sport funny black tufts in front of their ears. Juvenile marmosets don’t have white markings or ear tufts, so they don’t look nearly as cool as adult Geoffroy’s marmosets.

These marmosets live in family groups of 8-10 monkeys, which helps provide some protection for these small primates. They are particularly vulnerable to predation, so the group takes turns having a member act as a lookout. Groups forage, rest and hang out together. They are omnivorous, eating insects, fruit, plant gums, and other foods they can forage. They can gouge holes into tree trunks and other plants to obtain gum.

Look at that long tail! Image By Bjoertvedt – Own work, CC BY-SA 4.0

Each family group of marmosets has one dominant breeding pair – no other marmosets in the group are allowed to breed. The presence of a dominant female marmoset suppresses ovulation in subordinate females, ensuring she is the only one that can breed. Gestation lasts 140-148 days, and the female usually gives birth to twins. Her partner is a doting father, and helps out even with birth, licking the young before giving them to their mother. He also is the only one who will carry the babies in their first week of life. After that, he shares the duty, but still carries them for most of the time. The babies are weaned at 5 to 6 months, and reach sexual maturity at 15 to 18 months.

Despite a large amount of habitat destruction, the population of Geoffroy’s marmoset has been fairly stable, and they are quite numerous. They are also quite popular in zoos, where they are easy to maintain and breed. Some zoos even have to use methods to stop the animals from breeding, a nice problem for zoos to have.

Cover image By Norbert Kaiser – Own work, CC BY-SA 3.0, cropped to fit.