In "King Kong" it was beauty that killed the beast. In "Mars Attacks!" it was yodeling that killed the invaders.
The story: rodeo is the backdrop
Bromley declares this little creature to in fact be an eohippus. It has a name: "El Diablo."
Gwangi is able to break in. Many of the people flee through a back exit. "Tuck" has a torch and starts an interior fire which eventually kills the dino. There's your plot synopsis.
And: "(It's the) kind of tossed-off ephemera that does right by the eight-year-old hiding inside all of us."