Proto-Dravidian had a system of ten vowels consisting of five qualities ( i, e, a, o, u ), each with short and long counterparts. Some South Dravidian languages have expanded systems with innovative vowels that are described as centralized or retroflex. However, the phonetic nature of the vowels, and the list of languages that have them, remain poorly described. We present evidence that Muduga, a South Dravidian language of Kerala, is among the languages with expanded vowel systems. It has five innovative vowel qualities, three of which can be considered phonemic. Historical-comparative evidence indicates that the new qualities result from: (i) retraction of front vowels before retroflex consonants and alveolar /r/; and (ii) fronting of back vowels before alveolar and palatal consonants (except /r/ and /j/). Loss of conditioning consonants in some contexts has led to emergent contrasts. Acoustic phonetic analysis of two male speakers suggests that the new vowels are centralized along the front-back axis, but not retroflex or rhotacized. We compare these results to related developments in other South Dravidian languages and discuss correlations between retroflexion and retraction that motivate the observed patterns.