When Is A Monkey Really A Monkey?

A little boy pressed his nose on the glass where a Western Lowland Gorilla is interacting with the zoo-goers. He turns around to his parents with a big smile. “Oh look, the monkey wants to kiss you”, said his mother.

At the lemur exhibit, a girl asks her parents what those black and white primates were. Her dad picks her up and said, “It’s a monkey, sweetie … let’s go”.

A pair of gibbons gracefully swings around in their exhibit. Excited, a group of kindergarteners cheered as these gibbons maneuver around its habitat with great agility. “These monkeys are so active”, said the teacher.

If this sounds familiar to you then you are not alone. I spent a great deal of time near primate exhibits mainly because I love to observe their behaviors. I also enjoy watching interaction between humans and primates. However, there are times when I just can’t control myself and felt compelled to walk over to these people and explain to them that the word “monkey” is not a general term for primates (politely, of course). It shocks me that most of the time people do not read the information panel at the exhibit (aren’t zoo trips for educational purposes?). So when is a monkey really a monkey?

Monkey is a colloquial term for any cercopithecoids (Old World monkey) and platyrrhines (New World monkey). Monkeys are not hominoids (apes) or prosimians. One of the most distinctive characteristic that differentiate monkeys and apes is the presence of a tail in monkeys. Gibbons, siamangs, orangutans, gorilla, chimpanzees and bonobos are apes because they do not have a tail.

Gorillas do not have tails, so they are not monkeys but apes.

Differentiating monkeys and prosimians are a little tricky; all prosimians have grooming claws (toilet claws) but it is generally not visible within zoo exhibits. Prosimians include lemurs, lorises, galagos, aye-ayes and tarsiers.

A ring-tailed lemur is a prosimian. Although it has a tail, it also have grooming claws so lemurs are not monkeys.

A hamadryas baboon is technically a monkey because it has a tail but has no grooming claws.

The Barbary Macaque, Macaca sylvanus, was formerly named Barbary Ape due to the absence of a tail (to be more precise, they have a vestigial tail that looks like a stump). However, we know now that it is more closely related to macaques than to apes so its name was changed to correctly reflect what they are.

A Barbary Ape (notice the lack of tail). Flickr photo from Gerald Davison.

This brings us back to the question, “when is a monkey really a monkey’? The most straightforward answer would be “when it has a tail but doesn’t have grooming claws”. However, the most convenient answer usually lies in front of you … on the information panel.

Flickr photo taken by tim ellis at the Twycross Zoo, England.
The sign reads "Who are you calling a monkey?"

Algeripithecus and Azibius: Anthropoids or Strepsirhines?

The mandible of Algeripithecus. Photo from Science Daily.

The debate for the origin of anthropoid points to two locations. One hypothesis supports the notion that anthropoids originated from Africa while the other argues that anthropoids originated from Asia. The model for the African origin hypothesis rests on Algeripithecus minutus, a fossil discovered in Algeria, Africa that lived 45 million years old. Algeripithecus and Azibius are Eocene primates that lived around the same time in Africa some 50 million years ago.

Much more complete craniodental fossils of Algeripithecus and Azibius were recently excavated and reveal that they might not be anthropoids but were strepsirhines instead. New data from the fossils, according to a recently published paper by Tabuce et al. (2009), suggest that Algeripithecus and Azibius were the earliest primates to branch out of the Afro-Arabian strepsirhines clade.

According to Tabuce et al. (2009), there are anatomical evidence suggesting that Azibius were nocturnal. They also found that Algeripithecus has a long, thin and forwardly inclined lower canine alveolus, features that match the long and and flat lower canine in the tooth comb (dental comb) of crown strepsirhines. These physical characteristics suggest that both Algeripithecus and Azibius are closely related to crown strepsirhines. The researchers concluded that both Algeripithecus and Azibius were not members of the anthropoid family but instead an early representative of the crown strepsirhines. Crown strepsirhines gave rise to modern day lemurs, galagos and lorises.

Tooth comb of a ring-tailed lemur (Lemur catta). Notice the two lower canines that are long, thin and forwardly inclined. Together with four lower incisors, it makes up the tooth comb. Photo from Wikipedia.

These recently excavated fossils support the origin of crown strepsirhines from Africa. However, it also challenges the hypothesis that points to Africa as the origin of anthropoids since Algeripithecus should be classified as strepsirhines instead of anthropoids (and no longer provide evidence for the Africa origin hypothesis) according to this published paper by Tabuce et al.


References:

CNRS (Délégation Paris Michel-Ange) (2009, September 15). African Origin Of Anthropoid Primates Called Into Question With New Fossil Discovery. ScienceDaily. Retrieved September 15, 2009, from http://www.sciencedaily.com­ /releases/2009/09/090915101355.htm

Rodolphe Tabuce, Laurent Marivaux, Renaud Lebrun, Mohammed Adaci, Mustapha Bensalah, Pierre-Henri Fabre, Emmanuel Fara, Helder Gomes Rodrigues, Lionel Hautier, Jean-Jacques Jaeger, Vincent Lazzari, Fateh Mebrouk, Stéphane Peigné, Jean Sudre, Paul Tafforeau, Xavier Valentin, and Mahammed Mahboubi. Anthropoid versus strepsirhine status of the African Eocene primates Algeripithecus and Azibius: craniodental evidence. Proc R Soc B 2009 : rspb.2009.1339v1-rspb20091339.