[bluejay2]

You see this in Spanish a lot too. Diaz is son of Diego, which is still a common enough name. But there seem to be many more examples where the corresponding name is now rather uncommon from what I can tell. I am thinking of examples such as Menendez, Ortiz, Juarez, and Ordonez.

[mjd]

The examples that come to mind for me are Rodríguez, Martínez, González, Nunez, Hernández / Fernández, Sánchez.

Rodríguez, Martínez, and Hernández are the 9th, 10th, and 11th most-common surnames in the USA.

[pavel_lishin]

Both my endodontist and dentist have names ending in -ez, so I looked it up.

I wonder if this is a common pattern across all cultures and languages - if surnames share some sort of phonetic pattern, does it almost always indicate a patronymic, or (whatever the term for your profession/place of origin) is?

[mathieuh]

https://en.m.wikipedia.org/wiki/Proto-Indo-European_nominals

It comes from the Indo-European genitive.

[madcaptenor]

López, Gómez, Gutiérrez, Suárez, ...

[barreira]

Same in Portuguese but with an -es