With American toads and many related species (Woodhouse's toads, etc), the mature males have dark throats (see my avatar), much bulkier arms, and nuptial pads on the thumbs. If you look at the thumbs, the males have huge pads on the upper surface that make their thumbs look huge in comparison with those of females. My big male Woodhouse's toad retains the nuptial pads year round, but I am not sure if that is typical or not. I will try and get a few close-ups of my beast, partly because all these wonderful shots are making me want to try my hand at photography...