Fossil Platyrrhines

Late Miocene Amazonian Monkeys

- Greatest diversity and biomass of extant New World primates are found here, however, the fossil record is actually very limited → consisting of a few fragmentary fossils from the Late Miocene in brazil - 3 separate genera: - Stirtonia - broken lower molar placed here (although this genera is better known for deposits in La Venta) - Very large upper molar, similar to the Cebus genus, was placed into a new genera. - Solimoea → based on well preserved lower molar, indicates body mass of about 6 kg

Dolichocebus

- Nearly complete but damaged skull - - Medium sized Platyrrhine, the size of a titi monkey - Generally thought to be a stem Platyrrhine outside the extant radiation today.

Miocene of Colombia

- The best known fossil sites outside of the Patagonian deposits are at La Venta, Columbia - Many of the fossils here are strikingly similar to modern platyrrhines and clearly belong in living subfamilies - As opposed to the Patagonian fossils, which are much harder to place. - There are nearly a dozen species found here.

Kilikaike blakei

- found in the same part of Santa Crus as Homunculus - the anterior part of the cranium is similar in size and morphology - Many argue this should simply be a part of Homunculus

Homunculus Patagonicus

- from the middle Miocene Santa Cruz formation off the coast of Argentina - one of the earliest fossil platyrrhines discovered - medium sized monkey with 2.1.3.3. - Smaller brain than extant platyrrhines -

Rodent Record?

Also the S. American rodent fossil record, which appears slightly earlier than the primate fossil record is most closely related to the rodents known from the Eocene to present in Africa. There are no known anthropoids in N. America at this time so where could the stem platyrrhines have come from?

Why it is called Homunculus?

As the name indicates, researchers originally thought that the fossil was in the ancestry of humans - Studies have noted that dental similarities belong to Aotus and Callicebus - This is most likely a stem Platyrrhine outside the radiation of extant New World monkeys

The Patagonian Platyrrhines

Early and Middle Miocene deposits in Argentina and Chile! Like the early stem platyrrhines from Bolivia, these Patagonian fossils are broadly related to New World monkeys, however relationships to living subfamilies are difficult to come by.

The Platyrrhine Fossil Record

Fossil new world monkeys are relatively scare compared to the diversity observed in the Neotropics today and the relatively good fossil record for other S. American mammals.

Pleistocene Platyrrhines

In many cases, the most unusual platyrrhines are the youngest! 1) Proteopithecus brasiliensis: • The remains found in Pleistocene caves show small brains with defined nuchal and sagittal crests → combination suggest parallelism with atelids. 2) Caipora bamburiorum: • A second species found in the caves of brazil is larger than any of Platyrrhine at 17 kg! • Both cranial and skeletal remains resemble that of the Spider Monkey (ateles)

When do they appear?

The earliest appearance of platyrrhines in the fossil record come from the late Oligocene in South America. 5-10 mya after the Fayum primates South America was isolated for most of the Cenozoic Era and its isolation is reflected in the fossil record found there. It contains many unusual animals unique to the continent Currently the oldest primates found are from the Oligocene, however rodents were recently discovered in Chile from the late Eocene suggesting the there might be earlier primate fossils in South America as well.

Platyrrhine Origins

The most difficult and unsettling issue surrounding Platyrrhine origins is geographical: How did they get to S . America? S. America was an island continent throughout most of the Early Cenozoic, and connection was not made until the late Miocene One hypothesis states that the area in the South Atlantic was most likely very shallow due to crustal uplift and during times of low water levels, islands may have appeared crossing this gap and the gap would have been lessened Currents at the time would also have driven land mass from Africa to S. America.

Caribbean Primates

There are no extant Caribbean platyrrhines. This region may have once harbored a diverse fauna of unusual species however. Explanation for fauna? - Over-water dispersal from nearby parts of Central or S. America is most likely (Aloutta, Atele, and Cebus are all found in Cuba today) - However evidence also suggests that the Caribbean fossils are much different than extant forms living on the "mainland" today. - This would suggest that the fossils here were isolated for an extended period of time.

Summary of Fossil Platyrrhines

There is a general paucity of fossils in S. America, however, we are able to gain some insight: - Overall similarities between extinct species and current lineages - Although the evidence is limited to fragmentary dental remains, it would seem the platyrrhines have been distinct since at least the Middle Miocene - We also see some decreases in size (from the fossils found in Brazil) and decreases in diversity (from the fossils found in the Caribbean) demonstrating that the New World Pleistocene monkeys have clearly suffered dramatic extinctions

Asian Record?

There is slight evidence that Asia could be the origin, however an origin here would suggest that the primates would first have to cross through N. America and there is nothing in the fossil record to support this. There is no evidence of mammals on Antarctica or Australia prior to the arrival of humans which was much later.

The Earliest Platyrrhines

These fossils come out of the late Oligocene in Bolivia! There are two genera: They are small monkeys with 3 premolars and 3 molars. They differ only in the shape of the molars. 1) Branisella 2) Szalatavus this one has narrower, more triangular molars. Low rounded cusps suggest frugivorous diet. These two could be stem platyrrhines, but some have proposed a heavier callitrichid affinity for Szalatuvus because of the more triangular molars.

Also, in considering where the platyrrhines may have immigrated from, one must consider what source was likeliest to have them?

This is definitely Africa. There are also the most similarities between Eocene and Oligocene African anthropoids and extant platyrrhines

All evidence points to:

Thus all the evidence primarily points to primates arriving from Africa during the Eocene - - This requires an extended rafting trip, the likelihood of which is still highly debated - Given the dietary constraints of primates, this trip seems as if it would be more suitable for an organism that hibernates - Only a revision of paleocontinental maps or the timing of primate evolution could change the need for a rafting event - Rafting could be possible however if the sea levels were low enough.