Darkwing: I am the limestone that petrifies your bones.
The only two characters to cross over from Ducktales are Launchpad McQuack and Fenton/Gizmo Duck, however Scrooge Mcduck makes a small appearance on a billboard in the episode "Tiff Of The Titans"
Darkwing Duck is the only character to appear in every single episode.
This episode not only deals with fossils and time travel but is also a part of the Predestination Paradox, a paradox that exists when a time traveller is caught in a loop of events that "predestines" him/her to travel back in time. More Info
Last episode of Darkwing Duck.
The episode title is a play on the saying Distinct Possibility.