Digit wrote:Not all in one go Monk, it seems to have a been progessive rather than sudden. Take a look at the link I posted. Till the Drake passage opened there was no circumpolar current and antarctica is supposed to have been forested, this proposes a perfectly viable route.
Sorry Digit, you are probably undone by your posts. Prior to posting your animation, you posted this:
Geographic Distribution of the Platyrrhines (New World Monkeys)
They're only found in South America. Fossils go all the way south but species living currently only go a little out of the tropics. They maybe arrived 30 million years ago over the sea somehow- but it was not by a land bridge. Maybe they floated over on something?? Consider the great coincidence of it all- that a mating pair would both end up floating over the ocean at close enough to the same time so they could mate, they found each other, they found a land that was ecologically suited to them but had no other primates on it. This type of immigration is called an adaptive radiation- one species arrives somewhere and then diversifies into many
Emphasis mine.
The incredible thing is...this is considered plausible science.
I really cannot understand you people. How can you ask such questions when the answer is obvious ... monkeys were part of a Pleistocene Ringling Brothers excursion. Duh!
I can see herd animals and their predators crossing over the Bering Land Bridge to and from the Americas, but monkeys cannot do that. By the way, North and South America connected about 2.6 million years ago and monkeys have been in South America for up to 30 million years? What's up with that?
Last edited by Cognito on Fri Mar 30, 2007 11:08 am, edited 1 time in total.
One dispersal hypothesis suggests that primitive Asian anthropoids could have
invaded South America by an Antarctic route (Houle 1999). Even though a number of
primitive fossil anthropoids have been found in Asia, the lack of primate fossils in
Antarctica effectively discards this hypothesis (Kay et al. 1997). A second speculation, the
North-American origin of NWM, is also unlikely since no anthropoids were ever found in
that continent (Fleagle 1999). Finally, the morphological resemblance between platyrrhines
and the African anthropoid fossils, particularly those from Fayum deposits in Egypt, justify
the idea that the ancestors of Platyrrhini primates probably came from Africa (Ross,
Williams, and Kay 1998; Houle 1999).
Another hypothesis binds South American and African primates, but in the reverse
order. According to this last hypothesis, anthropoids could have originated in South
America and subsequently migrated to Africa (Szalay 1975). However, the lack of
prosimians in the South American fossil record sheds doubts on the validity of this
12
hypothesis. Furthermore, African anthropoid fossils date much older than South American
fossil primates, which are already recognized as Platyrrhini (Fleagle 1999).
Concluding, if an African origin for the South American platyrrhines is admitted,
the issue of how they made the journey remains to be clarified. The problem is that a
transatlantic journey from Africa to South America is not an easy feat for primates. It is
recognized that, in spite the overall unaltered disposition of continental landmasses, several
drastic climate changes marked the Eocene-Oligocene boundary (Ivany, Patterson, and
Lohmann 2000). These changes also include variation in global temperatures that may have
affected sea level. In this scenario, South Atlantic Ocean ridges such as the Sierra Leone
Rise and the Walvis Ridge could have become exposed as islands creating pathways that,
associated with favorable water and wind currents, enabled faunal migration to the isolated
South America (Houle 1999).
Indeed, other mammals have also supposedly invaded the South American continent
from Africa, such as New World caviomorph rodents that suddenly appeared in the South
American fossil record at approximately the same time as platyrrhines did (Wyss et al.
1993). Interestingly, these mammals, as NWM do, also have sister taxa relationship with
African groups, the phiomorph rodents (Mouchaty et al. 2001). Then, the existence of a
faunal connection between Africa and South America in the Eocene/Oligocene transition is
further corroborated.
The New World Monkey Enigma
The puzzling ancestry of New World monkeys derives from a low abundance of fossil material as well as limitations based on knowledge of continental drift. Similar biological diversity and geology suggest that the continent of South America was once a part of Africa. South America eventually broke off of the African mainland (through a geologic process called continental drift) and, over the course of millions of years, migrated to its present position. Unfortunately, the separation between South America and Africa occurred more than 100 mya, which is much earlier than the first primate fossils on either continent. This leads to several possible scenarios for the ancestry of New World primates:
African anthropoids crossed the Atlantic somehow and radiated into new habitats upon reaching South America.
North American primate forms gave rise to the current New World species.
African anthropoids emerged earlier than fossils suggest and rafted across the Atlantic when it was much smaller (Fig. 10-2).
Figure 10-2. A lighthearted view of the migration of New World
Monkeys. Credit: W.W. Norton
The problem with the first interpretation is the tremendous distance involved in a trans-Atlantic journey (by the late Oligocene that journey would have already been more than 2000 miles). Large chunks of land have been known to break off and essentially "float" across large bodies of water as living cargo vessels, although evidence has yet to emerge in support for this hypothesis for the origin of New World monkeys.
The second interpretation is problematic because North America does not have any evidence of anthropoid species. Thus descent from a prosimian-like common ancestor would require a remarkable number of evolutionary convergences between New World and Old World anthropoids, a concession many systematists find difficult to accept.
The third possibility provides a compromise of sorts between the first two explanations, suggesting that an ancestral primate form might have rafted across the Atlantic, but when the ocean was much smaller. This would push back the divergence dates for anthropoid primates beyond those supported by the fossil record; but as an old anthropological adage goes, "absence of evidence is not evidence of absence." Estimations of errors in fossil sampling suggest that anthropoids may have actually emerged as early as 52 mya. An earlier emergence of anthropoid primates might allow for a transoceanic voyage before the distance between South America and Africa became too great.
Bottom Line: We don't know how they got there, but there they are. Now take the same problem and expand it to other animal classes. Its mind boggling.
Digit wrote:Once again Monk I have say I don't get it? Explain please.
Your earlier reference stated that the new world monkeys did not arrive by a land bidge. Then you post the animation showing a possible anarctic land bridge. Your two posts contradict. Was there another post with an anarctica theory I missed?
My post above, debunks the anarctica theory as well.
Also - the divergence between new and old world monkeys is believed to be 30 million years but not much more.
Cognito wrote:I can see herd animals and their predators crossing over the Bering Land Bridge to and from the Americas, but monkeys cannot do that. By the way, North and South America connected about 2.6 million years ago and monkeys have been in South America for up to 30 million years? What's up with that?
I guess, Cogs, that would be the same land bridge that man DID NOT pass over as suggested by those old Jesuit monks, right? Or did I totally miss the mark on your previous post???
I guess, Cogs, that would be the same land bridge that man DID NOT pass over as suggested by those old Jesuit monks, right? Or did I totally miss the mark on your previous post???
It is reasonable to assume that groups of humans crossed over the land bridge in the Pleistocene in addition to arriving by boat, possibly at very early dates. In order to pull off the land trek they needed to deal with very cold temperatures. My point was simply this: monkeys could never make that excursion by land so Beringea is out. Further, North and South America were not connected until about 2.6 million years ago anyway. Yet, monkeys wind up in South America 30 million years ago. Why?
Don't misunderstand me posting contradictory links Monk. One of the things I complained to Steve about was the fact that tended only to post in his own support.
Let's look at this logically and take what we are certain of, accepted theory, and possible versus probable.
1. By what ever means the new world primates made it from the old world.
2. The new world primate species are younger that the old world ones and evovled from them.
3. That being the case what we are discussing is simply the route.
Surviving rafting across the southern atlantic is highly unlikely.
Before the Drake passage opened SA was connected to antarctica, antarctica was forested.
If the primates made it to SA 30 million yrs ago the may well have existed in antarctica well before that.
NW primates have never made it to north America but were in the far south. Old world primates reached the sourthern most part of Africa, therefore the logical deduction is that they made it from Africa to America via antarctica.
The absence of fossil records in antarctica in view of the present conditions would hardly be surprising.
What I have suggested may well be incorrect, but it is a damn site more logical than crossing the Atlantic.
Cognito wrote:
It is reasonable to assume that groups of humans crossed over the land bridge in the Pleistocene in addition to arriving by boat, possibly at very early dates. In order to pull off the land trek they needed to deal with very cold temperatures. My point was simply this: monkeys could never make that excursion by land so Beringea is out. Further, North and South America were not connected until about 2.6 million years ago anyway. Yet, monkeys wind up in South America 30 million years ago. Why?
I'm filing this one under "Unsolved Mysteries" with a side note to revise the Noah's Ark hypothesis.
The Antarctic Circumpolar Current formed during the Miocene epoch, when the pieces of the former supercontinent Gondwana which would become Antarctica and South America finally separated enough for the Drake Passage to form about 23Mya. As Antarctica was isolated from warmer waters it became progressively cooler, and glaciers began to form on the formerly forested continent.
From Wiki Monk, and if you check the distribution of monkeys on both continents, then allow the antarctic route, their range becomes a U shape conecting both groups.
Hmmmmmm....a breeding pair of monkeys floats over from Africa to S.A. to start the line of new world monkeys around 30 million years ago. Just an observation about odds here: if the odds were only one in a million that such an event would occur in any given year (an odds ratio I chose to illustrate this point, not necessarily the real odds) that still gives over a couple of dozen chances for such an exodus to happen. Who knows what the true odds are, but millions of years can add up to unlikely events occuring at least occasionally. After all, they had to get there somehow.
Some fat to chew on...a breeding pair is not enough to supply the genetic diversity needed for a viable population. Perhaps there was some "once in a milllion years" kind of storm that threw lots of trees (and clinging monkeys) into the South Atlantic all at once and enough got to S.A to start the whole New World line. Just speculating here with a bottle of Guinness, just speculating...
