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Strepsirrhini

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Strepsirrhini is a suborder of primates that includes several distinct groups of animals. This group contains the lemuriform primates, which include the lemurs of Madagascar. It also includes galagos, known as bushbabies, and pottos from Africa. Lorises from India and Southeast Asia are also part of this suborder.

Captive N. bengalensis from Laos with 6-week baby
Captive N. bengalensis from Laos with 6-week baby

Historically, this group also included the extinct adapiform primates. These ancient primates thrived during the Eocene epoch across Europe, North America, and Asia. While they are often called "lemur-like," they were actually quite different from modern lemurs. Today, most living strepsirrhines are arboreal, meaning they live in trees.

Strepsirrhines are defined by several specific physical traits. They possess a moist snout called a rhinarium. This wet nose is similar to the noses found on cats and dogs. The name Strepsirrhini comes from Greek words meaning "a turning round" nose. This refers to the winding, comma-shaped nostrils on their snouts.

They also have a vomeronasal organ, which helps them detect pheromones. These are chemical signals used for communication. Unlike many other primates, strepsirrhines have relatively small brains. However, they have large olfactory lobes, which are parts of the brain used for smelling.

GarnettsGalago CincinnatiZoo
GarnettsGalago CincinnatiZoo

Many specialized biological mechanisms help strepsirrhines survive in their environments. Their eyes contain a reflective layer that improves their night vision. This allows many species to be nocturnal, or active at night. Their eye sockets include a ring of bone, though they lack a thin bone wall behind the eye.

GarnettsGalago CincinnatiZoo
GarnettsGalago CincinnatiZoo

In their mouths, many lemuriform primates have a toothcomb. This is a specialized set of teeth in the front of the lower jaw. They use this tool to comb their fur during grooming. Another unique trait is their ability to produce their own vitamin C. This is different from haplorhine primates, which must eat vitamin C to survive.

The evolutionary history of these primates is a complex puzzle. Strepsirrhines diverged from haplorhine primates between 55 and 90 million years ago. Scientists use a molecular clock, which analyzes genetic data, to estimate these dates. The fossil record provides different, often younger, dates for these splits.

It is believed that lemuriform primates may have evolved from adapiforms like the cercamoniines or sivaladapids. These ancestors likely originated in Asia. Lemurs specifically reached Madagascar by rafting from Africa between 47 and 54 million years ago. Meanwhile, lorises split from African galagos about 40 million years ago and moved into Asia.

Adapiforms were a very diverse group of extinct strepsirrhines. They lived during the Eocene, which lasted from 56 to 34 million years ago. There are at least 30 known genera and 80 species of adapiforms in the fossil record. They are divided into three main groups: adapids, notharctids, and sivaladapids. Adapids were common in Europe but died out during a major extinction event. Notharctids lived in Europe and North America and looked very much like modern lemurs.

Notharctus osborni
Notharctus osborni

Sivaladapids were the only group to survive past the Eocene/Oligocene boundary. They lived in southern and eastern Asia until they disappeared around 7 million years ago.

Understanding strepsirrhine history helps scientists study mammalian evolution. For a long time, people incorrectly called lemurs "living fossils." This suggested they were "basal" or inferior primates that had not changed much. This view actually hindered scientific understanding. In reality, natural selection helped lemurs diversify to fill many different ecological niches. Even with smaller brains, they have successfully adapted to many environments. They show how specialized traits, like a reliance on smell, can drive evolution.

Today, many strepsirrhine species face serious threats to their survival. Habitat destruction is a major problem for these tree-dwelling animals. They also face pressure from hunting for bushmeat. Additionally, many are captured alive for the exotic pet trade.

Koh Kong logging
Koh Kong logging

These challenges make it vital to study their biology and history. By understanding how they evolved and how they function, researchers can better protect the diverse lineages that remain in the wild.

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🖼️ Images & Media (9)
File:Loris lydekkerianus nordicus 003.jpg
Loris lydekkerianus nordicus 003.jpg
File:Notharctus osborni.jpg
Notharctus osborni.jpg
File:Geoffroy72.jpg
Geoffroy72.jpg
File:Darwinius masillae PMO 214.214.jpg
Darwinius masillae PMO 214.214.jpg
File:GarnettsGalago CincinnatiZoo.jpg
GarnettsGalago CincinnatiZoo.jpg
File:Eulemur mongoz (male - face).jpg
Eulemur mongoz (male - face).jpg
File:Prosimian noses.jpg
Prosimian noses.jpg
File:Captive N. bengalensis from Laos with 6-week baby.JPG
Captive N. bengalensis from Laos with...
File:Koh Kong logging.JPG
Koh Kong logging.JPG
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