  Unit tangent bundles $UM$ of semi-Riemannian manifolds $M$ are shown to be
examples of dynamical Legendrian contact structures, which were defined in
recent work [25] of Sykes-Zelenko to generalize leaf spaces of 2-nondegenerate
CR manifolds. In doing so, Sykes-Zelenko extended the classification in
Porter-Zelenko [20] of regular, 2-nondegenerate CR structures to those that can
be recovered from their leaf space. The present paper treats dynamical
Legendrian contact structures associated with 2-nondegenerate CR structures
which were called "strongly regular" in Porter-Zelenko, named "L-contact
structures." Closely related to Lie-contact structures, L-contact manifolds
have homogeneous models given by isotropic Grassmannians of complex 2-planes
whose algebra of infinitesimal symmetries is one of $\mathfrak{so}(p+2,q+2)$ or
$\mathfrak{so}^*(2p+4)$ for $p\geq1$, $q\geq0$. Each 2-plane in the homogeneous
model is a split-quaternionic or quaternionic line, respectively, and more
general L-contact structures arise on contact manifolds with hypercomplex
structures, unit tangent bundles being a prime example. The Ricci curvature
tensor of $M$ is used to define the "Ricci-shifted" L-contact structure on
$UM$, whose Nijenhuis tensor vanishes when $M$ is conformally flat. In the
language of Sykes-Zelenko (for $M$ analytic), such $UM$ is the leaf space of a
2-nondegenerate CR manifold which is "recoverable" from $UM$, providing a new
source of examples of 2-nondegenerate CR structures.
