Many mammalian species have developed keratinized penile spines along the glans and/or shaft, which may be involved in sexual selection.
Upon withdrawal of a cat's penis, the spines rake the walls of the female's vagina, which may serve as a trigger for ovulation.
[7][8] They occur in wombats,[9] koalas,[10] spotted hyenas,[11][12] fossas,[13] echidnas,[14] primates,[15][16][17] bats,[18] and several rodent species.
[21] In contrast to chimpanzees, a common morphological variant found in humans called hirsuties coronae glandis, or pearly penile papules, are substantially larger, appear to be an outpocketing of both surface and underlying connective tissue layers, and lack the rich innervation seen in other animals.
[25] In some species which retain full expression, penile spines contribute to increased sexual sensation and quicker orgasms.