Wikipedia
Sharvara (Dog of Yama) is an ancient Hindu mythical dog belonging to Yama. It is one of the two dogs that guard the netherworld. Sharvara is identified with the constellation Canis Major, the other dog with Canis Minor, together they guard the gates of the netherworld, known as pitriloka or vaivasvataloka, which is the domain of Yama.
The word sharvara can mean variegated. Sharvara can be compared with the Greek Cerberus, the mythological dog of the Greeks with similar characteristics. However there is no description of Cerberus having a companion, and he is usually depicted with three heads. Scholars have concluded that the three heads were a Greek addition to the underlying Indo-Aryan myth.
Shavara can also be compared to Odin's wolves in Norse mythology. Odin (the all-father) just like Yama (the progenitor of all humans) sits on a chair guarded by two dogs. Although, Odin (Woden), the hunter, the wanderer, god of storm and winter, is more comparable to the Vedic Rudra.
Tilak dates the Vedic antiquity using the assertion that the Milky Way (path of the dead) used to be guarded by Sharvara and a new year started upon the crossing of Milky Way by the sun. Using internal evidence he dated the timeframe of Vedic antiquity (taittriya samhita) to the time when at the vernal equinox the sun rose in the asterism of Orion (Mrigashiras).