A nuptial pad (or thumb pad, nuptial ball,[1] nuptial excrescence[2]) is a secondary sex characteristic present on some mature male frogs and salamanders.[3][4][5][6] Triggered by androgen hormones, this breeding gland (a type of mucus gland) appears as a spiked epithelial swelling on the forearm and prepollex that aids with grip, used primarily by males to grasp (or clasp) females during amplexus.[7] They can also be used in male-male combat in some species.[7]
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Austrian biologist Paul Kammerer experimented on midwife toads' nuptial pads.[8] He used the offsprings' apparent enlargening from generation-to-generation as evidence of Lamarckian evolution.[9]
Many amphibian species manifest nuptial pads for use in amplexus, an example being the Rough-skinned newt, Taricha granulosa.[10]