Sequence and activity diagrams were already present in Jacobsons original method, which again is based on the "Ericsson Approach" (originating in 1967), long before UML; they were called interaction diagram and state transition graph.
Neither does "Ericsson Approach" for that matter..
The state transition graphs of Objectory (Jacobson's method) on the other hand originated in SDL process and procedure diagrams, which were issued in 1976 by CCITT as the Z101 to Z104 recommendations.