Which explanation for the dispersal of african monkeys to the new world is supported by the evidence?

Scientists have discovered the earliest known traveler between South and North America: a new species of monkey. It lived in Panama 21 million years ago, long before most scientists believe there was a land bridge connecting the continents. A plethora of monkey species lived in South America at the time, but it was then an island continent, cut off from its northern neighborhood by a seaway at least 160 kilometers wide.

So Jonathan Bloch was shocked when a postdoc sent him photos of fossils he had dug up while exploring ancient sediments in the newly expanded Panama Canal: They were monkey teeth. The teeth, encased in 21-million-year-old rock, were far older than any monkey teeth in Central America should be. In fact, until this find, the oldest monkeys in Central America were presumed to be less than 5 million years old, when many mammals stampeded over a land bridge between the continents.

Although the role of primates in seed dispersal is generally well recognized, this is not the case for colobines, which are widely distributed in Asian and African tropical forests.

Colobines consume leaves, seeds and fruits, usually unripe. A group of proboscis monkeys (Colobinae, Nasalis larvatus) consisting of 1 alpha-male, 6 adult females and several immatures, was observed from May 2005 to May 2006. A total of 400 fecal samples from focal group members covering 13 months were examined, with over 3500 h of focal observation data on the group members in a forest along the Menanggul River, Sabah, Malaysia. Intact small seeds were only found in 23 of 71 samples in Nov 2005, 15 of 38 in Dec 2005 and 5 of 21 in Mar 2006. Seeds of Ficus (all <1.5 mm in length) were found in all 3 months and seeds from Antidesma thwaitesianum (all <3 mm) and Nauclea subdita (all <2 mm) only in Nov and Dec, which was consistent with members of the study group consuming fruits of these species mostly at these times. To our knowledge, these are the first records of seeds in the fecal samples of colobines. Even if colobines pass relatively few seeds intact, their high abundance and biomass could make them quantitatively significant in seed dispersal. The potential role of colobines as seed dispersers should be considered by colobine researchers.