The 1830 edition accidentally omitted the repeated preposition by in this passage. Such prepositional repetition is characteristic of the Book of Mormon text and will be restored whenever the earliest textual sources support the repetition. For further discussion of the repetition of the preposition by, see under Alma 2:38. For a general discussion, see under conjunctive repetition in volume 3.
Summary: Restore the repeated by in Alma 16:10: “their carcasses were mangled by dogs and by wild beasts of the wilderness”.