Dogs of Roman Britain
Some modern dog book authors are of the opinion that these dogs were a distinct breed of dog , and that this breed was the progenitor to the English Mastiff and possibly the Bulldog . 
<triplet> English Mastiff <subj> breed <obj> instance of <subj> dog <obj> subclass of <triplet> Bulldog <subj> breed <obj> instance of <subj> dog <obj> subclass of