Through the years, the Batman has collected several trophies of past cases, some of them more famous than others. Among them are the giant penny of Joe Coyne, a giant Joker playing card... and the Robot Tyrannosaurus Rex. This one was encountered by Batman early in his career. After battling this mechanical beast in the Gotham amusement park called "Dinosaur Island" (II), he brought it back as a trophy, putting it on display in the Batcave for years. It was eventually lost when Gotham was struck by the earthquake called "the Cataclysm".
[Although Batman and Robin fought the Tyrannosaurus Rex in "The Isle That Time Forgot" (Batman #11) it was an Apatosaurus (a.k.a. Brontosaurus) that first showed up in the Batcave. Not until the 1950s, it was retconned into a T-Rex. In 1997, the island from which it originated was retconned from a movie set into an amusement park.]