From Halopedia, the Halo wiki
The Tankbeast is a deleted Covenant species revealed by Bungie employee Paul Russel on Twitter. The Tankbeast would have stood roughly 3.5 meters (11.4 Foot) tall, with no visibly-distinct head. The Tankbeast also had an underslung weapon, and with armored legs and body. It may have been an inspiration for the Lekgolo.