OG12 CR78，难题求助！！！

OG12 CR78，
Fossils of the arm of a sloth found in Puerto Rico in 1991, and dated at 34 million years old, made it the earliest known mammal of the Greater Antilles islands.

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

麻烦考友了！！我想问一下正确选项D： sloth，found in Puerto..... 中的found是被发现，所以谓语动词是have been found对吗？然后是三个平行：have be found.... have been date...，have been making....
看到e-gmat.com上：Certain fossils were found in Puerto Rico in 1991 and are 34M years old.
只用过去被动时不用have been那不是不平行了吗，但是如果用完成时又不对，请问如何平行呢？
Fossils were found ___ and have been dated ___ made it _____.

babybearmm的解释：
这道题正确句子的主干：
Fossils have been dated at 34 million years old.
修饰成分插入在空格位置：
Fossils _____, ______, have been dated at 34 million years old, ____.

关于A，我觉得最大的问题是主干的逻辑意思不对，提炼下A的结构：
Fossils (found ___, and dated ___,) made it _____.

第一，从逻辑上看，我用括号包围的部分应该是noun modifier that modifies "fossils", 那么这里标点符号就存在严重问题，应该是以下两种表达之一：
Fossils found ___ and dated ___ made it _____. （无逗号）
Fossils, found ___ and dated ___, made it _____. （一前一后逗号成对）

第二，还是从逻辑上看，是"dated at ...."造成了"made sloth the earliest known mammal ..." 这个大家都能理解吧
所以A的句子逻辑就不对，而正确句子D，恰恰体现了这种逻辑关系

http://e-gmat.com/blogs/?p=285
的解释Understand the meaning of the sentence and determine the logical antecedent
Per the sentence:
Certain fossils were found in Puerto Rico in 1991 and are 34M years old.
当中是were found。

比较og12 sc84的解释，D omitting the main verb, is, results in a sentence fragment, 如果是were found但是没有were那就是sentence fragment。

found到底和什么平行呢? many, many thanks!!