Convert a mesh object to a mesh sequence object by selecting the object, clicking Object > Convert to Mesh Sequence.
Add new mesh frames and keyframes by clicking (in the Object Properties panel) Mesh Sequence > Advanced > Duplicate Mesh Frame or by performing the hotkey Ctrl+Shift+D
Convert a mesh object to a mesh sequence object by selecting the object, clicking Object > Convert to Mesh Sequence. Add new mesh frames and keyframes by clicking (in the Object Properties panel) Mesh Sequence > Advanced > Duplicate Mesh Frame or by performing the hotkey Ctrl+Shift+D