Callosity

A callosity is a type of callus, a piece of skin that has become thickened as a result of repeated contact and friction.

[1][2] The pads enable the monkeys to sleep sitting upright on thin branches, beyond reach of predators, without falling.

[7] Callosities arise naturally and are present even in late-term whale fetuses, although the work of lice digging into the surface of the skin may make them more jagged and hard over time.

[citation needed] Callosities are found on the upper surface of the whale's head: above the eyes, on the jawline and chin, and surrounding the blowholes.

[citation needed] It has also been proposed that the barnacles attached to callosities are important in helping fend off attacks by orcas.