Legendrian cone structures and contact prolongations

We study a cone structure ${mathcal C} subset {mathbb P} D$ on a holomorphic contact manifold $(M, D subset T_M)$ such that each fiber ${mathcal C}_x subset {mathbb P} D_x$ is isomorphic to a Legendrian submanifold of fixed isomorphism type. By characterizing subadjoint varieties among Legendrian submanifolds in terms of contact prolongations, we prove that the canonical distribution on the associated contact G-structure admits a holomorphic horizontal splitting.