[Evolutionary aspects of hair polymorphism]

Abstract

Polymorphism of hair was considered in terms of their origin in mammalian evolution. Vibrissae significantly differ from hairs by the structure. Apparently, they originated from mechanoreceptors of Cotylosauria and developed only in the Theriodontia-Cynodontia-Panthotheria-Theria lineage (Metatheria, Eutheria). No vibrissa developed in the lineage of Theriodontia-Cynodontia-Prototheria (Multituberculata, Triconodonta, Monotremata), where mechanoreceptors or glandular structures of amphibian ancestors transformed into electro- and mechanoreceptors. Hairs originated in these lineages in parallel from keratin epidermis in correlation with the establishment of homeothermy but independently of vibrissae. Wide and active adaptive radiation provided for a strong differentiation of hairs largely similar in different taxa. Spines originated by heterochrony of hair generations.