From http://www.eclipse.co.uk/thoughts/animalsouls.htm with slight modifications by the author of the site:
St. Paul said that animals would be redeemed.
Thomas Aquinas is regarded as an authority as denying that animals have souls but contradicted himself elsewhere writing: 'we 'must use animals in accordance with the Divine Purpose lest at the Day of Judgment they give evidence against us before the throne' (source currently unavailable - please write in if you know it).
In a public audience on January 19th 1990 Pope John Paul 11 said "also the animals possess a soul and men must love and feel solidarity with smaller brethren" He pointed out that in Genesis "the way in which man was created suggests a relationship with the spirit or the breath of God. And one reads that after having created man from the dust of the earth, the Lord God 'breathed life into his nostrils and man became a living soul.'" He went on to say that animals have the breath of life and were given it by God. So, in this respect, man, created by the hand of God, is identical with all other living creatures. Although the pope's statement was reported in the Italian press it was not reported in the UK and was ignored by British Catholic publications. (His comment was passed off by some as meaning that animals have souls but that this does not impy they have the same kind of souls as people - people having immortal souls and animals only mortal ones. Now we have the beginnings of a complicated theology! A two tier soul system! What rights and privileges does having a mortal soul confer upon you? Surely this will become the centre of intense debate within the Catholic Church - or perhaps they'll just ignore it altogether :-)
Martin Luther certainly believed animals went to heaven "Be thou comforted, little dog," he said. "Thou too in Resurrection shall have a little golden tail." (Note that Martin thought animals had 'immortal' souls.)
Much more recently John Austin Baker, the former Bishop of Salisbury, and a champion of animal rights commented - "Thomas Aquinas and the scholastic tradition said very clearly that animals have not got souls and this has been used in the past to justify any exploitation of animals on the grounds that they are just things. Others have said that animals' consciousness was so limited that they needed to be appendages of good human beings to be capable of enjoying the life in heaven. But that puts paid to 99.9% of all living creatures. You surely don't have to have high rational intelligence like human beings in order to have the possibility of a relationship to transcendent or eternal life." (So he thinks that animals probably do have souls.)
Shouldn't Christians become Vegans just in case?
Sadly, none of these signs are real: