Sentence:  ... "great beasts that resembled huge brown haystacks" and had long, long teeth — tusks, no doubt — so it seems incontrovertible that mastodons and woolly mammoths are meant. Such <WSD>pachydermic</WSD> animals did roam Maine once upon a time. 
Meaning of the word marked with <WSD> tags:  Pertaining to the obsolete taxonomic order Pachydermata.