Complex sentence: The Goddard site has been dated to 1180-1235 (ie well within the circulation period of pennies of this type) and the people living there at the time are generally considered to be ancestors of the Penobscot.
Split into simpler sentences: The Goddard site has been dated to 1180-1235, within the circulation period of pennies of this type. The people living there at the time are generally considered to be ancestors of the Penobscot.