Weather is what exposes fossils. Ice cracks rock. Gradually fossilized bone is revealed. So weather is the fossil hunters friend, it reveals what had been hidden. But weather is also the fossil hunters worst enemy because an unfound fossil is gradually erased, just like the rock that surrounds it.
Timing is everything.
Now, there isn t much in the way of high tech equipment in fossil hunting, just a good pair of boots and very experienced eyes. To inexperienced eyes, fossils pretty much look like rocks. Tinker revealed himself in the form of a couple of claws and a few pieces, only partially exposed but visible enough for talented eyes to recognize. Tinker was just beginning to be revealed. This is just plain lucky.