Different vowel endings in Italian surnames?

[Kelleygen]

While researching my Martinelli relatives, I came across a census that lists them as Martinello - with an o instead of an i. This was weird as I have always heard it with an i, so I thought it was the census taker's mistake.

Later, however, I found a document filled out by my ggrandfather, where he filled out his name as Luigi Martinello, yet, and this was the weird part, he SIGNED his name as Luigi Martinelli. I was wondering if anyone has come across this. I thought it may have something to do with the Italian singular/plural being o/i, respectively. You know, referring to themselves in the singular but their family name as a whole in the plural?

[Italysearcher]

I have seen a lot of this kind of thing and I believe it is a singular/plural thing.

[Barga]

NO its not plural

Its Latin The i ending means belonging to

eg Name Piero = Peter Pieri = Belonging to Peter Its NOT Italian Its
Latin

[misbris]

Barga,

I have always wondered at the "is" ending as in Leonardis, De Angelis, De Sanctis, De Santis. Is that Latin rather than Italian also? Why did some names remain Latin and others change to Italian?