It sprouted in my veggie beds, from premature composting (a habit I can’t seem to kick.) The seed it sprouted from was large, and roughly resembling a squash seed. A sucker for a good mystery, I saved it from the spading and put it in a seed tray indoors. Let’s hope it grows large enough to solve the mystery!
plumdirt 
It probably IS a squash, but if you had more than one variety growing close by last season, it might not be what you’re expecting…squash hybridize very easily!
We had more than a few in our compost pile last summer!
Ah, that could very well be! I’m used to squash sprouts that are smooth rounded leaves that come up like praying hands and then open flat.
I had some DELICIOUS mystery squash (probably a skewed version of the grocery store hybrid) last year. Unfortunately, the squash bugs agreed with me…