[1] A diagnostic innovative feature in the Ndu languages is the replacement of the proto-Sepik pronoun *wun ‘I’ with proto-Ndu *an ~ *na.
Most Sepik and neighboring languages have systems of three vowels, /ɨ ə a/, that are distinct only in height.
Within words, /ɨ/ only occurs between similar consonants, and seems to be explicable as epenthesis there as well, so that the only underlying vowels that need to be assumed are /ə/ and /a/.
[1] Ndu languages mark first and second person possessors with -n, and third person possessors with -k.[1] wunɨ-nə1SG-POSSmbalɨpigwunɨ-nə mbalɨ1SG-POSS pig‘my pig’ndɨ-ku3SG-POSSmbalɨpigndɨ-ku mbalɨ3SG-POSS pig‘his pig’wun-(n)a1SG-POSSmaːmolder.siblingwun-(n)a maːm1SG-POSS older.sibling‘my elder sister’ndɨ-kɨ-ndɨ3SG-POSS-M.SGyaːmbroadndɨ-kɨ-ndɨ yaːmb3SG-POSS-M.SG road‘his road’Ndu languages make use of the general locative case suffix -mb (-m in Manambu):[1] kwalɨneckkambɨlɨ-mbəriver-LOCkwalɨ kambɨlɨ-mbəneck river-LOC‘at the source of the river’ŋgu-aːmwater-LINK.LOCŋgu-aːmwater-LINK.LOC‘in water’ Unknown glossing abbreviation(s) (help);Ndu languages have two dative-type case markers, with the forms and meanings varying across languages:[1] Examples of dative case markers in Ambulas and Manambu:[1] ndumanmbɨrɨPLtakwəwomanmbɨr-ətPL-ALLndu mbɨrɨ takwə mbɨr-ətman PL woman PL-ALL‘toward the men and women’ɲjɨmbaworkyə-kwədo-PRSndu-kɨman-BENɲjɨmba yə-kwə ndu-kɨwork do-PRS man-BEN‘for the men who work’ar-aːrlake-LINK.ALLyi-tɨkgo-1DU.SBJ.IMPar-aːr yi-tɨklake-LINK.ALL go-1DU.SBJ.IMP‘Let’s both go to the lake.’ Unknown glossing abbreviation(s) (help);a-ndɨthat-M.SGɲɨnɨkchild.LINK.BENa-ndɨ ɲɨnɨkthat-M.SG child.LINK.BEN‘for that child’ Unknown glossing abbreviation(s) (help);Dative case markers are also used to mark animate objects of transitive verbs, which is a Sepik-Ramu areal feature.
An example of the Ambulas allative case marker -t:[1] wunɨ1SGɲan-ɨtchild-ALLkenək-kwəscold-PRSwunɨ ɲan-ɨt kenək-kwə1SG child-ALL scold-PRS‘I’m scolding the child.’Reconstructed proto-Ndu pronouns by Foley (2005): Note that there is a gender distinction for first-person pronouns.