Carl and Frank are a pair of brontothere rhinos who appeared in the first Ice Age film.
The pair appeared at the beginning of the film when clumsy Sid the Ground Sloth was shown stepping on their salad and eating the most important part of it, the dandelion. This last act angers them both to the point of wanting to kill him, but as they were about to, they were stopped by Manny the Woolly Mammoth, by being hurled through the air.
They held a powerful grudge against Sid for what he had done, and when they next saw him, he was in the same hot mud pool, that they were in and was erroneously referring to them as ladies. Carl and Frank, remembering everything that Sid did to them, stampeded after the hapless sloth, but were waylaid when they saw that he had already been "killed" by Diego the Saber-Toothed Tiger, which was part of Sid's plan to get them to be fooled into leaving him alone and not trying to kill him, so they gave up their chase post-haste, angrily.
Then in the Ice Age Dawn of The Dinosaurs video game they returned for revenge on Sid and tried to hit the playground but they were defeated by Sid and forced to give up after they hit the ground and the rocks. NOTE: They didn't appear in the actual movie.