A paper given at Stanford on the 29th: “Pronouncing the Z’s: Epenthesis in English plural possessives” by Simon Todd (a Ph.D. student in linguistics). The beginning of the abstract:
The interaction between the English regular plural affix (PL) and possessive clitic (POSS) presents a theoretical puzzle (Zwicky, 1975). Both have the form /z/, and so the OCP [AZ: Obligatory Contour Principle] (Yip, 1998) predicts their combination (PL+POSS) should trigger epenthesis. Yet, in cases like my friends’ /fɹenz/ car, only PL is overtly realized. Why does the OCP fail to apply?
Two previous theories address this non-application of the OCP in PL+POSS constructions. The POSS-suppression theory (Stemberger, 1981; Zwicky, 1987) claims that POSS essentially inspects the morphological composition of its host and is actively suppressed by adjacent PL /z/, without exception. The alternative POSS-allomorphy theory (Bernstein & Tortora, 2005; Nevins, 2011) claims that POSS has a phonologically null allomorph, which is chosen when the possessor has the plural feature. Either POSS allomorph may be chosen for a singular possessor with embedded PL; thus, contra the suppression theory, epenthesis may be triggered in cases like the son of my friends’s /fɹenz ~ fɹenzəz/ car.
(Some of this is seriously technical, but try to get the drift.)
The crucial paper of mine comes from about 30 years ago, and the question can now be examined with tools that weren’t available then.