A continued role for signalling functions in the early evolution of feathers

Persons and Currie (2015) argued against either flight, thermoregulation, or signalling as a functional benefit driving the earliest evolution of feathers; rather, they favoured simple feathers having an initial tactile sensory function, which changed to a thermoregulatory function as density increased. Here, we explore the relative merits of early simple feathers that may have originated as tactile sensors progressing instead towards a signalling, rather than (or in addition to), a thermoregulatory function. We suggest that signalling could act in concert with a sensory function more naturally than could thermoregulation. As such, the dismissal of a possible signalling function and the presumption that an initial sensory function led directly to a thermoregulatory function (implicit in the title “bristles before down”) are premature.