We came across this treed Porcupine in our travels. Porcupines are the second largest North American rodent next to Beavers. S/he was about 60 ft up in the air. I'll post a pic in my other album to give you sense of the whole scene. I had other pics that showed the body and tail a bit better but this is the only one that showed the teeth! Yuck!
The distinguishing feature of porcupines is their quills along their back and tail. The Lethbridge College web sites says "quills are easily dislodged and penetrate the flesh of a potential predator. Microscopic barbs on the tips of the quills serve to pull the quills deeper into tissue. Quill penetration can cause infection and in severe cases, the eventual death of an attacker. Adult quill sizes range from 2 – 10 cm. Larger Porcupines may have as much as 30,000 quills distributed throughout the body."
@lynnb thanks lynn! i haven't looked at the college web site in detail but from what i've seen, it's very good for animal info. sounds like a nice college.