The two appeared at the beginning of the film when Sid the Ground Sloth was shown stepping on their salad and eating an important part of it, the dandelion. This last act angers them to the point of wanting to kill him, but as they were about to, they were stopped by Manfred 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. Again, Carl and Frank 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 off, so they gave up their chase post-haste, defeated. Carl had thick lips and a thick horn, while Frank had more pointed lips and a thinner horn.Carl is an Embolotherium and Frank is a Megacerops.