"Say: "Shall I point out to you something much worse than this, (as judged) by the treatment it received from God? those who incurred the curse of God and His wrath, those of whom some He transformed into apes and swine, those who worshipped evil;- these are (many times) worse in rank, and far more astray from the even path!" (The Noble Quran, 5:60)"
"When in their insolence they transgressed (all) prohibitions, We said to them: "Be ye apes, despised and rejected." (The Noble Quran, 7:166)"
"And well ye knew those amongst you who transgressed in the matter of the Sabbath: We said to them: "Be ye apes, despised and rejected." (The Noble Quran, 2:65)"
Reading this few ayahs slowly we can come to a conclusion that there were some humans that Allah S.W.T. transformed into apes and swine. But why apes and swine and not other animal? Why not snake or dog or fish? Why not lizards or camels or scorpians or chickens or birds or any other animals?