The trouble with tribbles

The worthy pathfinder Amarilla was recently wondering what these are. I thought immature or under-developed sweetgum pods. But those are green and fruity looking, so I retract that suggestion. Today I found some of the mystery tribbles (way too much wikip here for you youngsters) under a planetree... but it's too early for this year's planetree seed balls, and what's left of last fall's don't look like this. Besides, location doesn't necessarily mean anything (see H.D. Thoreau's "trout in the buttermilk").