[R. Scott]

So then wouldn't everything in that niche have reamined the same …

The rat squirrel adapted well to fill a particular niche. It had adapted well and no further change was necessary.

[metmom]

The niche didn't change for 11 million years? If the niche did change then the rat squirrel wouldn't have been so well adapted for it, and would theoretically, therefore had to change to fit the new niche.