- dicynodontA member of the infraorder Dicynodontia of dominant herbivores of the Late Permian, the most successful group of non-mammalian synapsids.
- diergismThe existence, in a single species, of two distinct ways of a structure or organ functioning.
- dimicticHaving two thermal overturns per year.
- distrixThe splitting of the distal ends of the hair.
- ditokousHaving two kinds of young, such as offspring from asexual reproduction versus those from sexual reproduction.