Age: 20 million years ago

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

Time Period: Middle Miocene

Fossil: Skull
http://cryptomundo.com/cryptozoo-news/new-skulls/

Middle Miocene Time Period

Fossil: Right upper first molar
http://morphosource.org/index.php/Detail/MediaDetail/Show/media_id/7431

All New World monkeys have been found to have a single M/L photo-pigment 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 trichromoatic. 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.
http://www.sciencedirect.com/science/article/pii/S0042698998000789

http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1415-47572004000300007

Chromosome numbers in New World monkeys range from 16 in the titi monkey to 62 in the wolly 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 wolly) shows that there is also a wide range of evolutionary relationships within the platyrrhines. The chromosme numbers show how New World Monkeys as a whole have evolved together, but also shows how specific monkeys have changed within the Platyrrhines.

Less than 500,000 years ago

Fossil: Complete Skeleton
http://pages.nycep.org/rosenberger/pdfs/Halenar%20and%20Rosenberger%20JHE%2013%20(Cartelles).pdf

Each of these Cebidae monkeys have around the same number of chromosomes. The monkeys A,B, and D have 44 chromosomes total and the Goeldi’s marmoset has 46. This shows that they are all very closely related, but those three with 44 are even  more closely related. Also, the Goeldi’s marmoset has different sex chromosomes because it has both a X1 and X2 chromosome unlike the rest of the monkeys. This shows how this marmoset is less like the other monkeys. Human’s have 46 chromosomes and one X and Y chromosome. These karyotypes of monkeys show close similarities to Humans. The monkeys have either 44 or 46 chromosomes, which show striking similarities between these monkeys and humans and show that they are closely related ancestrally. The Goeldi’s marmoset is very similar because both the human and those monkeys have 46 chromosomes. They are different because humans have one X, while the marmosets have a X1 and X2 chromosome. The other three monkeys are close to humans because they have 44 chromosomes , which is very close to 46 and they have one X and Y chromosome just like humans.