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).

《冰河世紀》中的席德是一只地獺，同現在動作遲緩的樹懶是近親，看這性格脾氣、行動風格，也實在相去甚遠。

巨型地獺，居住在數萬年前的阿根廷彭巴斯大草原，又名美洲大地懶。這種動物生活在距今約1萬年至10萬年前的南美洲大陸，為當時體型最大的哺乳動物。身高可達6公尺，體重約5噸，前肢和后肢都具有強壯且尖銳的爪子。可以直立，并能用它那強壯的手臂與巨大的爪子將整個樹枝拔下。它也是在第四紀大冰川期滅絕的。