Scrat is a sabre-toothed squirrel who is obsessed with collecting acorns, constantly putting his life in danger to obtain and defend them. He has his own stories in the film which mostly independent of those of the main characters, though the two do intersect at times.

In a special feature in the second film’s DVD, his name has been stated to be a mix of the words “squirrel” and “rat”, his species allegedly believed to have been a common ancestor of both. In the Ice Age DVD commentary, he is referred to as “The Scrat” by directors Chris Wedge and Carlos Saldanha. Scrat is never referred to by name in dialogue, but only named in the credits.

Quelle: https://en.wikipedia.org/wiki/List_of_Ice_Age_characters#Scrat