Mammals do not have diversity interms of flying species...

[handbanana]

Mammals are the most advanced but yet we're not diversed enough to have more flying species..
Why is that? Why we only have the bat?

[mith]

perhaps there hasn't been that much evolutionary pressure to take the skies.

[nornerator]

Mammals are not the most advanced in any way.

Your question assumes a directional sort of evolution.

All species of life are as advanced as any other species.

As mith posted before me, it is all based on selective pressure.

If there was a very strong pressure for some reason for mammals to take to the sky, mammals would either evolve to take to the sky, or die. Obviously most mammals have not been under the kind of selective pressure necessary for this adaption.

[alextemplet]

How are you defining "advanced"? If you're defining advanced in terms of being able to survive in a particular ecological niche, then yes all organisms are equally advanced (at least until they become extinct!). However, I'm used to seeing advanced defined as complexity, in which case some organisms are more advanced than others.

[mcar]

Most mammals had adapt on land--more advantage the land does create or give. So why go up and fly, afterall that smog filled the sky nowadays--

[Darby]

The bats are the second largest mammal group, after rodents.

Lumping them together the way you have, you could just as easily as to why only the bird?

[AstusAleator]

forgetting bugs?

[February Beetle]

Does anyone know about the time distance between when birds took to the skies and mammals started to diversfy more into their modern extant families?
I know insects had the skies taken up long before any vert walked onto land (right? I guess it's hard to distinguish 'long')
Dinos died off and small mammals survived and began to diversify to fill the empty nitches

When did birds diversify?

[alextemplet]

I think birds already had a bit of diversity going on during the Cretaceaus, but I think they really took off (pun intended) after the extinction of the dinosaurs, just like the mammals.

[February Beetle]

Hmm... I really want to take a paleontology class. Do you think it will deal with questions such as these?

[alextemplet]

I would hope it would.

[auglyorgan]

The niche has been filled by birds. Would be pretty hard to out compete them after they have adapted to the skies for millions and millions of years.