It's an opossum - Didelphis virginiana. I realize that I could have given you a better scale to work with. The skull is about 5-6 inches in length, and it's sitting on the hitch of the boom-pole for the tractor.
Here are some fun facts about 'possums as told to me by Farmer John as he read out of his "Mammals of Minnesota" field guide:
- Gestation is 12-13 DAYS, at which point they crawl unassisted into the pouch.
- The brain cavity of a possum can hold 26 navy beans. (While a similar sized raccoon's brain cavity can hold 139 navy beans.)
- They are popular table-fare in southeast Minnesota. Which, I swear, came straight from the book!
And so concludes your nerdy-naturalist lesson for the day.