The St. Canard Natural History Museum is one of the calmer museums in St. Canard courtesy of its collection not containing any easy loot. Even so, it has been targeted at times and more importantly produced a villain, Dr. Fossil. Relatedly, it is also the origin area of Justice Ducks member Stegmutt.
The St. Canard Natural History Museum is located in a cube-shaped building thematically enhanced by an artifical tar pit right next to it. It is either three or four storeys high and has a bunker-basement, although the basement might be the unauthorized work of the paleontologist Dr. Fossil, who was employed at the museum before going bad. Being obsessed with dinosaurs and a genius, he created the retro-evolution gun with which he turned himself into a pterodactyl and began a scheme to turn more people into dinosaurs and then wipe out the rest of mankind so dinosaurs would rule once more. The museum served as his base of operations during this time. Either as assistant or as test subject, he also turned the not-so-bright janitor of the museum into a stegosaurus and dubbed him Stegmutt. Stegmutt served him well until he became aware of Dr. Fossil's true plans and switched sides to help Darkwing Duck. Dr. Fossil's contract was ended after this and Stegmutt, a hazard to the dispalys due to the combination of strength and clumsiness, either left or was laid off by the museum and began a career as hot dog vendor.
After turning himself and Stegmutt into dinosaurs, Dr. Fossil sends Stegmutt on various errands to bring him various types of people and animals to also prehistorically mutate. Stegmutt performs well at first, avoiding detection, but when he abducts Shyster and Loophole Darkwing Duck gets on the case. That is, the crimefighter makes the wrong deductions and goes after the wrong criminal, but Honker Muddlefoot, accompanied by Gosalyn Mallard, follows the trail of stegosaurus footprints to the museum. They meet Stegmutt at a dinosaur display and the former janitor offers to show them the basement where he and his friends live. Dr. Fossil is not happy to have intruders, especially not because he ordered circus elephants, but as Stegmutt reveals secret after secret he rolls with it. When Stegmutt is gone, he tells the children about his plan to wipe mankind with Cleanser's Comet and give dinosaurs another chance as the dominant species through his collection stored safely in the reinforced basement. He furthermore reasons that smart kids will do just as well as circus elephants and locks them up to retro-evolve later. By the time Stegmutt returns from a military facility with the super-magnet to draw in the comet, Darkwing has realized his error and trailed the stegosaurus to the museum's roof. While Stegmutt goes to the basement to turn the children into dinosaurs, Darkwing does battle with Dr. Fossil. Honker and Gosalyn inform Stegmutt of Dr. Fossil's plan and convince him to help stop the mad scientist. They go up to the roof with the retro-evolution gun, but Darkwing is accidentally hit by its ray. He topples off the roof into the tar pit below and would have drowned were it not for his mutation turning him into a storeys-high dinosaur. With Cleanser's Comet heading their way, Dr. Fossil tries to reach the basement, but Darkwing blocks the entrance with his foot. The pterodactyl flies off to lead Darkwing away, which means saving the world from a comet impact is up to Honker, Gosalyn, and Stegmutt. Honker figures out that they need to change the super-magnet's direction; a feat of strength only Stegmutt can accomplish. He gladly helps and coincidentally incapacitates Dr. Fossil in the process. With disaster averted, Stegmutt's friends are freed and all involuntary dinosaurs reverted to their old selves.