Colobinae

Colobinae are a diverse subfamily of Old World monkeys known as leaf-eating monkeys.

This group includes 61 different species across 11 different genera. Notable members include the black-and-white colobus and the large-nosed proboscis monkey. Most species are arboreal, meaning they live primarily in trees. However, some species lead a more terrestrial life on the ground. They inhabit many environments, such as rainforests, mangroves, and mountain forests. You will not find them in dry deserts or other arid areas. They are medium-sized primates that usually possess long tails.

The pig-tailed langur is a rare exception to this tail rule.

These monkeys are specialized folivores, which means their diet consists mostly of leaves. To process these tough plants, they use a process called foregut fermentation. This occurs within their complex, multichambered stomachs. Inside these chambers, bacteria work to break down hard-to-digest plant material. The bacteria also detoxify plant compounds before they reach the intestine. This process allows the monkeys to extract higher levels of protein and fiber. This method of digestion is similar to that of cattle, deer, or kangaroos. This differs from New World howler monkeys, which use hindgut fermentation in the colon.

Scientists classify the Colobinae into different groups based on geography and biology. One common classification splits them into two distinct tribes. The tribe Colobini is found in Africa and contains three genera. These include the black-and-white colobus, the red colobus, and the olive colobus. These African genera are unique because they possess stub thumbs. This physical trait is why their name comes from the Greek word "kolobos," meaning "docked."

The other tribe is Presbytini, which is located in Asia. This Asian group contains seven genera and is often split into two further groups. These are known as the langur group and the "odd-nosed" group.

The Asian Presbytini group contains very diverse species. The langur group includes the silvery lutung and the gray langur. The "odd-nosed" group includes the proboscis monkey and the snub-nosed monkey. Scientists use mitochondrial DNA (mtDNA) to study these evolutionary relationships. While the Asian species form two clear groups, the gray langur's exact placement is debated. Some studies suggest they are not closely related to the other groups. Other studies place them firmly within the langur group. This complexity shows how much there is still to learn about primate evolution.

The history of the Colobinae is written in the fossil record. The earliest known remains were discovered in the Tugen Hills of Kenya. These fossils date back approximately 12.5 million years. In Eurasia, the oldest fossils belong to a genus called Mesopithecus. These were found in Greece and date to about 8.2 million years ago. Researchers believe the two main tribes split between 10 and 13 million years ago.

This long history has allowed the monkeys to spread across different continents.

Evolutionary history in this subfamily is also shaped by hybridization. Hybridization occurs when different species mate and produce offspring. Research suggests that "introgression," or the movement of genes between species, played a major role. For example, females from the Piliocolobus or Procolobus genera may have influenced the Colobus genus. In Asia, males from the Semnopithecus genus may have influenced the Trachypithecus genus. In India, gray langurs are known to hybridize with Nilgiri langurs. These genetic exchanges helped shape the unique relationships we see in monkeys today.

Colobines exhibit several interesting biological traits and life patterns. The coloration of young animals often differs remarkably from the adults. Socially, they live in groups, though their specific social forms vary. In species like the silvery lutung, females begin reproducing around three years of age. Unlike the Cercopithecinae subfamily, colobines do not have cheek pouches for storing food. These specialized traits, from their complex stomachs to their unique thumbs, make them a vital part of the primate world. They connect various ecosystems through their role as specialized herbivores in many different habitats.