So according to the new core rules:
25.5.1 CONDITIONAL BATTLEFIELD ROLES Sometimes, the Notes column on a Pitched Battle profile will tell you to change the battlefield role of units of that type if certain conditions are met. For example, choosing a certain model to be your general can mean the battlefield role of certain units changes to Battleline. Where this is the case, unless noted otherwise, the unit loses all of the battlefield roles in the Battlefield Role column of its Pitched Battle profile and just has the battlefield role specified in the Notes column instead.
It means youre Stegadons are Troops in Thunder Lizard when it comes to battalions.