Aristotle was the first to indentify the soul as the source of life and being in anything. Thomas Aquinas wrote that an animal does have a soul, as it is a being. The animal soul, as defined both Aristotle and Aquinas recognized that the soul is not located in any specific part of the body but is a part of the total being. As the Catholic belief is that humans are instilled by God with an immortal soul, Aquinas could not say conclusively that the soul of an animal would also be eternal, but he did state that it was unproven as such but not observable in the same capacity as the human soul, given the post-mortem activity of certain saints and the resurrection of Christ on the third day to give example of what we should expect at the end of time. As far as animals having a soul? Well, the intelligence level is arguably not the same as a human, but it certainly does have a soul as it has being. Is it immortal, we'll have to find out in God's time. But for the time being, love your animal, if for nothing else, as a wonderful gift from God that brings His creation and friendship with you in a meaningful way. Since Heaven will provide us with wonderful surprises, so your animal may be there for you; as with God, all things are possible. For fun, look up the poem "The Hound of Heaven"