A number of common English surnames are the same as common English given names, with the addition of an "S." Examples are Peters, Daniels, Michaels, Matthews, Roberts, Phillips, Isaacs, Williams, etc.
What is the root cause of this phenomenon? Is it related to the formation of surnames from patronyms? Most of that same list also has common variations ending in "-son" (Peterson, Danielson, Robertson, etc.)
Note: I did a Google search around this question, but the results all had to do with pluralizing a surname, or making it possessive.
Best Answer
According to Mckinley's A History of British Surnames, the major rise of surnames derived from a personal name with the addition of -s or -es was among the "peasant" classes in the late 13th century. These people didn't have hereditary surnames of their own, so the implication is that they adopted their master's name as befitted their social status as they were bonded to him. If you follow that logic, it primarily signified whose property they were as much as anything, although the passage in that link doesn't wholly explore this.
There was then a second wave of Welsh -s names that appeared more widespread in the British Isles in the 16th century. Together with the earlier English 'mutation', that generated most of the -s names we see today.
So they're not quite patronyms, then, but close.