From Halopedia, the Halo wiki
A degaeorth is a giant predatory beast native to Doisac.
Degaeorths are known to stalk prey in Doisac's dense forests. Each has a single fearsome horn that juts from above its snout and a crest made up of two flanking plates that swing backward to either side of its head. The Jiralhanae chieftains of the Covenant wore similarly shaped helmets which paid homage to these features, increasing their imposing stature by a considerable margin. 
List of appearances
- Halo: Envoy (First mentioned)
- ^ Halo: Envoy, pages 40-41