Two of you guessed right! The skull (last week's post) was that of a squirrel. I got my first clue when I found a muskrat skull online. The teeth were the giveaway. Of course, the muskrat was a lot bigger. Obviously I needed to look at smaller rodents and zeroed in on either sciurus carolinensis (Grey Squirrel) or sciurus niger Fox Squirrel. But that's as far as I could go. There might be a slight size difference between the Fox and the Grey, but I haven't the knowledge or the ability to distinguish further.
Thank you everyone for your responses! What fun!!!