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<<Betty's right: what I was actually referign to was a big brown bat;
what I first thought of as a megachiropteran appears to be a very
large microchiropteran, which small ears and a very unmodified nose
(it looked like a megachiropteran, just very small and the head does
look similar to micros), and I don't know much of the differences
between the two groups. Matt's refs on mirco polyphyly may have
something to say, but anyway, I have only a few things on bats, and
most of these are on micros. Sorry.>>

Microchiropteran polyphyly has been suggested, yes, but I usually talk 
about CHIROPTERAN diphyly.  That is, the controversy over whether or not 
Megachiroptera+Microchiroptera form a monophyletic group.  John 
Pettigrew has been the most vocal on this issue, basing his arguments on 
the fact that megabats and primates (including the colugo) share several 
(a few dozen) nervous system specializations not found in microbats.  
Bat diphyly is nothing really new; Hill and Smith have suggested this 
many times during the 70s (again, shared characters between megabats and 
primates not found in microbats; this time penial characters).  Also, 
there is some molecular evidence that supports diphyly in bats.  All in 
all, I think that the case for bat diphyly is pretty strong, but it 
needs more osteological and myological data, something that proponents 
of bat monophyly have.  

How do you tell a megabat from a microbat?  Its relatively easy.  Most 
megabats are relatively large, while microbats are for the most part, 
very small (certain cryptozoologists believe that there are some 
microbats with 3 meter wingspans; I don't buy it for a second).  
Megabats have a claw on the index finger, while extant microbats lack 
it.  Megabats hang from branches colugo-style, using forelimbs and 
hindlimbs, while microbats use only hindlimbs.  Microbats frequently 
nest in large colonies in the deep recesses of caves, while megabats, 
excluding some species of _Rousettes_, _Dobsonia_, etc (these bats only 
nest around the entrance of caves in not in large groups), tend to stray 
away from caves, preferring trees.  Megabats universally have large eyes 
that they use to navigate with, while microbats have small eyes.  
Megabats do not have a specialized ear structure, while microbats 
usually have a very complicated ear with a tragus and antitragus in the 
caudal portion.  Megabats also tend to be more 'cute', while many 
microbats, especially those with noseleafs, tend not to be.  Except for 
some species of _Rousettes_, megabats do not employ echolation (note 
that the megabat species with echolation use a echolation form that is 
considered non-homologous to the form that microbats use); microbats, 
except for some extremely abberent species, use echolation.  Megabats 
are universal frugivores and nectorivores, while except for some South 
American microbats, microbats do not have anything to do with flowers. 
There are a lot more characteristics for each group (such as locomotion, 
more diet stuff, geography, parental care, dentition, reproduction, 
etc.) but I will give you this list to finish with.

Matt Troutman 

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