In addition to normal generation, they can be summoned by the summon nasties monster spell.
By the time a player normally encounters them, baluchitheria should not be a threat. In terms of nasties, others such as the master mind flayer or minotaur are much more threatening, and an individual baluchitherium can be dealt with easily.
Baluchitheria are prehistoric creatures that resembled modern rhinos, but possessed longer necks, had no horn, and were about three times bigger.
Extinct rhinos include a variety of forms, the most
spectacular being _Baluchitherium_ from the Oligocene of
Asia, which is the largest known land mammal. Its body, 18
feet high at the shoulder and carried on massive limbs,
allowed the 4-foot-long head to browse on the higher branches
of trees. Though not as enormous, the titanotheres of the
early Tertiary were also large perissodactyls, _Brontotherium_
of the Oligocene being 8 feet high at the shoulder.