Lemur of mouse lemurs, the gray mouse lemur ("M. murinus"), golden-brown mouse lemur ("M. ravelobensis"), and Goodman's mouse lemur ("M. lehilahytsara") were considered the same species until recently, when genetic tests identified them as cryptic species. The lemur dentition is heterodont (having multiple tooth morphologies) and derives from an ancestral primate permanent dentition of . Indriids, sportive lemurs, the aye-aye, and the extinct sloth lemurs, monkey lemurs, and koala lemurs have reduced dentitions, having lost incisors, canines, or premolars. The ancestral deciduous dentition is , but young indriids, aye-ayes, koala lemurs, sloth lemurs, and probably monkey lemurs have fewer deciduous teeth.
Language acquisition by deaf children but do not use sign language have better communication outcomes and social well-being than Deaf children who use sign language. The general stages of language acquisition are the same whether the language is spoken or signed. There are certain unique features of sign language acquisition due to the visual/manual modality and these differences can help to distinguish between universal aspects of language acquisition and aspects that may be affected by early experience. The very earliest linguistic tasks facing newborns are perceptual. Babies need to determine what basic linguistic elements are used in their native language to create words (their phonetic