Ultima Online: The Second Age, which was released on October 1st, 1998 and Ultima Online: Renaissance which was released on April 3rd, 2000.
Savage Ridgebacks -
I found these UO:R Critters in the Compassion Desert, hidden away in a small cave with some Savages northwest of the shrine. These creatures didn't appear until 2001 in Scene 2 - The Gargoyles Redemption. My source = http://www.uoguide.com/Ridgeback