...if you look carefully you can see a dark pattern of stripes behind all that caked-on mud. Cricket Frogs come in a variety of colors, from muddy brown, to grey, tan, or greenish. Our little guy definitely falls in the muddy brown category, although he does have mud and sand on him, parts are mud-free, showing as grey-brown.
A Cricket Frog's call sounds a little like a marble dropped on cement, slow at first, sounding once or twice a second and then increasing until it becomes a continuous rattle lasting about 30-40 seconds (source: "Amphibians and Reptiles of Indiana, Sherman A. Minton, Jr., 117). Click here for a recording of their call.
...the interesting pattern of bars on his upper lip reminds me of a skull!
Cricket Frogs have a dark, triangular spot between their eyes on the back of their head (Minton, 115). Our frog's triangle was a bit hard to see, but it was visible. I outlined it to make it easier to spot.
Our little frog is probably getting ready to hibernate. I read here that they seek out crayfish burrows or cracks in ponds or along the bank to hibernate in. They usually are tucked away for the winter by early November (Minton, 117). "Sleep" well little guy!