an evolutionary puzzle, new world monkeys

I don't know about that...probably opportunity is the only requirement...the dodo gave up flight for the simple reason it wasn't required, there was an opportunity, no predators and ample food on the ground...

 

Ok, picture this. It is known that evolution proceeds much faster among small, isolated groups (genetic drift etc.). When the African savannah went through a drying episode, the rainforest split into patches separated by grasslands. Hence the monkey populations were also split. Then these patches also began changing into grasslands, and the small monkey populations had to evolve fast to keep up with changes. I remember reading somewhere about a drying episode in South America (5 million years ago?), where the rainforests receded, but not as extensively as in Africa. And size would definitely make a difference as far as cold preadaptation is concerned. You cannot compare cool tropical nights to northern winters.

 

yup very plausible...

my research showed the rainforests retreated into remnant forests of Central America...but even if i were to accept your version there is still no reason for monkeys not to take advantage of a new open niche, life hates a vacuum...

still disagree, size is not a issue there are very small mammals that do absolutely fine in frigid climates, they adapt... many animals found in southern climes have made cold weather adaptations...snow monkeys of japan endure -20f winters, no bigger than new world monkeys with an average weight of 10-11kg, they adapted by growing much thicker fur than southern species...

they're different but both are dangerous... desert cold is dangerous because low humidity causes very low nightly temps, animals need to keep cool in day time temps in the 50c range and warm when it drops to 0c and lower, very difficult conditions to survive in, over heating and hypothermia are always a danger...winter in the north is probably easier to deal with for an mammal, it's cold day and night, grow a thick fur winter coat and wait for spring...

 

adding to my previous response to this post where opportunity plays a part yes you are correct as well, punctuated equilibrium or strong evolutionary pressure plays a part as well...

as my daughter tells me there is no simple formula for evolution there is more than one road to reach the same point...

 

And what small mammals do well in frigid climates? Insectivores and rodents. What do they have in common? Fast metabolism, which requires high calorie intake per day. This keeps them warm and comfy in a wasteful kind of way. Most monkeys don't distinguish themselves with such high metabolism. There are some like tamarins and marmosets that may approach this, but then again, what do they eat? Insects, fruit? Are those abundantly available throughout winters? The Japanese macaques and their Chinese equivalents are both large. Size does matter.

 

Such small mammals also burrow or hide in shrubs to stave off weather. Primates don't do this.

 

rabbits are out all winter long same for fox, weasels, mice and others, when temps get down as low as -40 or even -50 there is much staving off done it's still (*)(*)(*)(*) cold...

 

the point you've missed is animals adjust their diet as needed when adapting to a new niche, some bats are insectivores and hunt by sound others have become fruit eaters and find their way about by sight and smell...most piranha are meat eaters some are not...some early hominids were omnivores and others preferred a strict plant diet...new world monkeys were not restricted to any diet they were free to adapt to what ever conditions and diet that presented itself...

nope, japanese macaques are about the same size as a new world howler monkey, and as I posted earlier fossil remains of new world monkeys were double the size of japanese macaques...and Howlers are larger than arctic hare or fox...and arctic hare don't burrow, nor are there trees or shrubs to shelter under,a small animal, bitter cold yet it adapted because there was an open niche to fill and it did...insulation not size is the critical adaptation to cold and mammals do it well, reptiles not so much...

 

and some bears hibernate and others do not, hibernation is adaptation to low winter food supplies... saying primates can't adapt while bears did isn't realistic...primates can adapt as well as any other mammal they are not locked into a fixed state...

 

Nope, haven't heard of a single primate that can hibernate. Hibernation is a special adaptation involving a drop in body temperature etc. Additionally, primates don't burrow or hide in caves which goes together with hibernation. I guess north of Mexico, squirrels is as close as you're gonna get to primates (except for a few vicious chimps that mauled their owners and then ran off into the wild, but I wouldn't torture your daughter with these tales).

 

you're being silly denying primates are capable of evolutionary adaptation merely to defend your position....if bears, hares, fox can find adaptations to cold climes so can primates....


oh and here's a hibernating primate..
.

 

a quick recap
-we have evidence of small snow monkeys equal in size to new world primates living in a cold climate by adapting with better insulation...
-we have evidence of equally small old world monkeys living in grasslands despite numerous predators...
-we have evidence of new world monkeys being twice as large as today's species...
-we have evidence of a primate hibernating in shelters...
so the question remains unanswered, why over 5 million years haven't new world monkey's not adapted to the open niche that was N america...or did they and fossil remains have yet to be found been...

 

There was no such evolutionary pressure which existed in the Old World to force well specialized arboreal animals to leave their niche and exploit ground-dwelling and at the same time cooler habitats. There were apparently some experiments, but they all seem to have failed. So why don't you examine why they failed, like that fossil monkey from Texas. Perhaps if you knocked off all the squirrels in North America, primates would come. Fill in the niche vacuum.

 

Ok, forget what I said about a fossil monkey from Texas. It turns out this was not even a monkey, but an Eocene prosimian.

http://www.upi.com/Science_News/2011/05/16/New-fossil-primate-found-in-Texas/UPI-43051305593272/

So I guess the New World monkeys were simply too well adapted to their arboreal lifestyle, even better than their Old World counterparts. Consider for example that Platyrrhines have prehencile tails while Cattarhines don't. This put them at a disadvantage against other animals with a more generalized bodyform to compete effectively in more open landscapes. Or perhaps it's the other way around. Primates are known to have a very generalized skeleton. In North America, the forests have not receded or advanced much, so primates were quite successful where they lived, but did not feel much adaptive pressure to leave their habitat and change profoundly in order to effectively compete with specialized prairie animals who inhabited these ancient unchanging grasslands for eons and eons.

Here is an article which asked the same questions as you and may be related to your research.

http://books.google.ca/books?id=44-...onepage&q=monkey fossil north america&f=false