GMAT OG12 语法78题中date的用法？

OG12 78中date的用法有错误！！

Fossils of the arm of a sloth found in puerto tico in 1991, and dated at 34 million years old, made it the earliest known mammal of the Greater Antilles Islands.(选D)
(A) sloth found in Puerto Rico in 1991, and dated at 34 million years old, made it the earliest known mammal of
(B) sloth, that they found in Puerto Rico in 1991, has been dated at 34 million years old, thus making it the earliest mammal known on
(C) sloth that was found in Puerto Rico in 1991, was dated at 34 million years old, making this the earliest known mammal of
(D) sloth, found in Puerto Rico in 1991, have been dated at 34 million years old, making the sloth the earliest known mammal on
(E) sloth which, found in Puerto Rico in 1991, was dated at 34 million years old, made the sloth the earliest known mammal of

别的都明白了，就是一个细节，不应该是sth date back....(某物追溯到...时期)吗？为什么正确答案中是sth is dated back呢？date表述追溯的意思的时候应该用主动形式还是被动形式呢？