The gemarah says that in the first Beis Hamikdash the fire on the alter looked like a crouching lion and in the second Beis Hamikdash the fire on the alter looked like a crouching dog. The MARSH"A explains that since the first Beis was built by Shlomo Hamelech the fire took a regal shape of a lion, while the second Beis was built by the kings of Persia, who were compared to dogs, the fire took the lowly shape of a dog.
What still bothers me is; the Chaza"l write in many places that the dog is one of the lowest creatures on the planet, why would G-d "bring" this animal into the holiest place on the planet?