In my notes from Monro, μερόπων ἀνθρώπων is “a conventional epic word, the meaning of which is unknown” other than it refers to mankind.
The LSJ gives:
dividing the voice, i. e. articulate (cf. Hsch., Sch.11.1.250), “μ. ἄνθρωποι” Il. l.c., Hes.Op.109, etc.; “μ. βροτοί” 11.2.285; “μερόπεσσι λαοῖς” A.Supp.90 (lyr.): hence as Subst., = ἄνθρωποι, Musae.Fr.13 D., A.Ch.1018 (anap.), E.IT1263 (lyr.), A.R.4.536, Call.Fr.418, AP7.563 (Paul. Sil.); a usage satirized by Strato Com., 1.6 sq.
The LSJ revision adds some information, but nothing relevant to this usage. The scholia, referenced by the LSJ, gives this story:
μερόπων ἀνθρώπων: μεμερισμένην τὴν φωνὴν ἐχόντων, ὡς πρὸς συγκρισιν τῶν ἄλλων ζώιων, ὅ ἐστι μεριζομένην εἰς συλλαβὰς καὶ ἔναρθρον ἐχόντων τὴν ὄπα, τουτέστιν τὴν φωνήν.
μερόπων ἀνθρώπων: men having the “divided sound,” expressing a division from the other animals, which is divided into syllables and having the articulate (jointed) voice, this is the sound [they have].
The above is my translation (please correct). I thought this sounded like the fanciful creation of someone trying to guess the original meaning from the parts, and it looks like Leaf agrees:
μερόπων, an epithet of which the real sense was in all probability forgotten in Homeric days, as it is used only in purely stereotyped connexion with ἄνθρωποι (exc. B 285, q.v.) We can only say with confidence that it does not mean “articulate,” μερίζοντες τὴν ὄπα, as in so ancient a word the ϝ of ϝόψ would not be neglected. The other derivations which have been proposed are quite problematical.
The reference to B 285 concerns the children of Μέροψ. Is there any chance that this usage was original, and crept into other parts of the Iliad? Are there any other good suggestions?