The voiced dental spirant developed from primitive [d] after vowels, and also medially from the voiceless dental spirant [θ] (PE19/23), which itself developed from the primitive aspirate [tʰ]. As such, it could not appear at the beginning of an Ilkorin word.
References ✧ PE19/23
|ᴹ✶-khj- > -ðı̯-||[-kʰj-] > [-xj-] > [-θj-] > [-ði-]||✧ PE19/23|
||✧ PE19/23 (-d- > -ð-)|
||✧ PE19/23 (-th- > -ð-)|