  We give necessary and sufficient geometric conditions for a theory definable
in an o-minimal structure to interpret a real closed field. The proof goes
through an analysis of thorn-minimal types in super-rosy dependent theories of
finite rank. We prove that such theories are coordinatised by thorn-minimal
types and that such a type is unstable if an only if every non-algebraic
extension thereof is. We conclude that a type is stable if and only if it
admits a coordinatisation in thorn-minimal stable types. We also show that
non-trivial thorn-minimal stable types extend stable sets.
