A dog is a domesticated form of canine, often kept by many as pets.
A pet dog called Sprat, belonging to Taylor Craig, went through an anomaly. Taylor followed it through, and, along with Nick Cutter and Stephen Hart, got stranded in the Silurian. Sprat made it back through, before Taylor, Nick and Stephen did too. (Episode 2.5)
During a Hyaenodon incursion during the wedding of Jenny Lewis, it was noted several times that the creatures bore a resemblence to giant dogs. However, the two species are not actually related. (Episode 4.6)