Sid is a ground sloth shown in all three films as one of the main characters. While he is always called "Sid", Sid's full name is Sidney, as revealed by his would-be paramour Sylvia.

Ground sloths are a diverse group of extinct sloths, in the mammalian superorder Xenarthra. They may have died out as recently as 1550 AD in Hispaniola and Cuba, but had long since been extinct on the mainland of North and South America. The term "ground sloth" is used as a reference for all extinct sloths because of the large size of the earliest forms discovered, as opposed to the extant "tree sloths." However, this is an historical convention and does not imply that all extinct sloths were strictly terrestrial in nature. The megalonychid ground sloths first appeared in the early Oligocene, about 35 million years ago, in southern Argentina (Patagonia).

《冰河世纪》中的席德是一只地獭，同现在动作迟缓的树懒是近亲，看这性格脾气、行动风格，也实在相去甚远。

巨型地獭，居住在数万年前的阿根廷彭巴斯大草原，又名美洲大地懒。这种动物生活在距今约1万年至10万年前的南美洲大陆，为当时体型最大的哺乳动物。身高可达6公尺，体重约5吨，前肢和后肢都具有强壮且尖锐的爪子。可以直立，并能用它那强壮的手臂与巨大的爪子将整个树枝拔下。它也是在第四纪大冰川期灭绝的。