funeral rhetoric - prose vs. verse

I'm writing an essay on Brutus' and Mark Antony's speeches, and I am puzzling over why Brutus' speech is in prose while Mark Antony's is in iambic pentameter. Anyone got any ideas?

I haven't read Julius Caesar, but isn't iambic pentameter considered as the noble verse? Shouldn't it give more weight and authority - maybe traditional, old-fashioned authority - to what Marc Anthony says? Whereas prose is more down-to-earth and less respectful of tradition and especially form and therefore formality)? As I know that Brutus ends up killing Caesar, I imagine he wasn't that resepctful of his elders and of conventional hierarchy, no? It reminds me of when Richard III suddenly says "thou" rather than "you" to other characters - in general, he's showing lack of respect for propriety (and for his interlocutor).
Bottom in Midsummer Night's Dream (and the other villagers too, I think) speaks in prose, and this is to contrast him with the flowery verse of the fairies. With him too there's a reversal in the traditional order, since he ends up kissing (and not treating very well) the queen of the fairies.

Well, I know that usually, the less noble characters all speak in prose, but Brutus speaks in iambic pentameter all through the rest of the play, it's only during his funeral speech that he uses prose. Also he's much older, and I think more universally respected than Mark Antony. So I really don't understand it.

It does seem odd that Brutus speaks in prose at this point since he's certainly capable of using verse effectively. I've come to believe that he uses prose because he wants to explain and defend the conspirators' action without the aid of rhetorical flourish. Brutus hopes to describe why Caesar had to be killed by using plain language. He wants to appear reasonable and unemotional to make it clear to the people that the murder was not an act of malice but a political action to ensure the vitality of the republic.

Well Shakespeare obviously wanted to make this distinction... Mark Antony speaks in flowery, eloquent speech, and Brutus in plain and simple speech. This perhaps was just the effect that Shakespeare wanted--to see the simplicity of language, and perhaps sincerity of words... Mark Antony's speech, however, is more convincing to the public and rouses them... This goes to show how powerful rhetoric is and how manipulative words can be. For words do mask true motivations... With this, Mark Antony plays on the people's emotions, while Brutus plays on their reason. Emotions prevail in the end (as they usually do in Shakespeare's plays, or at least initially).

there is a lot more that can be said about this, and perhaps many different interpretations, but I will just throw that out there for now...

I'm currently also studying Julius Caesar, and my assumption on the prose vs verse is that Brutus speaks to the plebeians in prose to be understood by them better.
The crowd/commoners never speak in iambic pentameter. So Brutus thinks that this is the best way on how to direct them.

However, as Antony speaks in iambic pentameter, he is treating the crowd as an equal to himself.

This might seem confusing, that you might think that Brutus would treat himself as an equal to the crowd by speaking the same way as they do.
But I don't think that this is the case.

As Antony speaks to them formally in iambic pentameter, he is treating them highly as well. Talking in the same way that Antony would inform other members of e.g. the senate. He speaks to his own rank in iambic pentameter, so he uses the same method and speaks to the commoners in iambic pentameter too.
The crowd will feel important. And after all, this is a public play.

I hope I have provided some help.

Brutus’s speech to the plebeians after Caesars death is in prose to emphasise his honesty and sincerity. This honesty and sincerity contrasts with the deceptive methods used by Mark Antony. Mark Antony's speech in contrast is extremely superficial and contrived. He uses flattery of the audience, repetition, irony rhetorical questions etc. While Brutus' speech is honest and open, his motives are clear compared to Antony who hides his want of revenge.

Characterisation is therefore the reason that Shakespeare uses prose here.