Black Headed Spider Monkeys are very nimble, and have very long arms. They have prehensile tails and hook like hands. They have a spider like appearance and have no thumbs. They have front facing eyes and nostrils that are very far apart. They have black faces, but are born pink. They are between 40 and 55 centimeters long and are around 9 kilograms. 

These animals prefer to grab things with their tail, and they search for food during the day. They prefer to eat fruit, but will eat seeds, bark, leaves, spiders, nuts, and small insets. They spend most of their day in trees, swinging and climbing. They live in large communities of 20-100, and give birth to babies every one or two years. These babies are carried on mothers stomachs. After they get a little older, they are carried on the mother's backs. When female spider monkeys are ready to mate, their scent and behavior changes. They do not have a specific mating season, and will mate any time during the year. They are very intelligent, and have strong memories. They are also very social and noisy. They are most intense during the day, and at night, they split into half a dozen or fewer to sleep. They reproduce sexually.

Taxonomy
Kingdom: | Animalia
Phylum: | Chordata
Class: | Mammalia
Order: | Primates
Family: | Atelidae
Genus: | Ateles
Species: | A. fusciceps

  

 

Age: 20 million years ago

Fossil: Skull
http://digimorph.org/specimens/Tremacebus_harringtoni/

All New World monkeys have been found to have a single M/L photopigment gene on the X chromosome. This gene limits males to have dichromatic or monochromatic color vision. Only heterozygous females for the gene were trichromatic. Male howler monkeys have recently been found to have more than one M/L pigment gene, and both are uniformly trichromatic. These observations show DNA similarity between all new world monkeys because they have the M/L gene that codes for pigment. Evolution is shown in the howler monkey because it has 2 of the genes and it always codes for trichromatic vision, unlike the other monkeys. This shows how the howler monkey has differently evolved. Also, new world monkeys such as marmosets have the common gene WFIKKN1. This gene is turned on in New World Monkeys, specifically marmosets, that encodes for the twinning process in reproduction. This shows DNA similarity in new world monkeys and also how marmosets have evolved to have this occur more often and for the gene to be more active.
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Chromosome numbers in New World monkeys range from 16 in the titi monkey to 62 in the wooly monkey. There are many close numbers between new world monkeys such as the silvery marmoset, pygmy marmoset, and Common Squirrel Monkey with 44 chromosomes and the Goeldi’s marmoset with 46 chromosomes. These similarities show how close new world monkeys are similar to each other. Because these four monkeys have such close chromosome number this shows that they are evolutionary similar. In addition, the wide range of chromosome numbers within new world monkeys (titi to Wooly) shows that there is also a wide range of evolutionary relationships within the platyrrhines. The chromosome numbers show how New World Monkeys as a whole have evolved together, but also shows how specific monkeys have changed within the Platyrrhines.
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Anatomy and physiology
Anatomical

New world monkeys have broad faces, widely spaced noses, long tails, and a vomeronasal organ. These traits have been passed down from older new world monkeys in the platyrrhine. This shows evolution because these traits are similar through several generations and have been passed on to other platyrrhines. These structures such as the vomeronasal organ have shown evolution in new world monkeys from other organisms with their structure such as humans because it has evolved to become different in monkeys.