Reins of the Raven Lord

Reins of the Raven Lord summons Raven Lord, an ground mount that requires 150 Riding skill to ride. It looks like a hybrid between a raptor and bird. However, as a ground mount, it does not actually allow the rider to fly.

Source
This item drops off Anzu, who appears in the heroic version of Sethekk Halls. The drop rate, according to external data sites, seems to be less than 1%. As of patch 4.0.1, Anzu is always present in the instance and no longer requires a druid to summon.