Continuous Lines from Isolated Splotches

[dozerman]

Pic related was extracted from an image of a fossil by using wavelet decompose and the selection tool. I want the eventual image to be a kind of stencil of the skeleton's outline. I'm almost to where I want to be, but I can't figure out how to connect all of the disparate splotches into one continuous outline without doing it manually. 

I've already tried messing with the threshold on the select tool without much luck.

[rich2005]

Plenty cleaning up required but maybe something like this.

Colors -> Levels and move the left and center slider over to the right to darken the image.

   

Apply Filters -> Blur -> Gaussian Blur to the result . The default 1.5 is ok

   

Then Colors -> Threshold and move the left side slider across almost to the right side. Small values make a big difference, you can use the left side value box to fine tune.