D选项是不是做同位语呢？又因为同位语不像定语状语那样要求就近修饰，所以它就没有紧挨着fossils。
可是老师我记得你说过同位语从句的先行词是要是抽象名词的啊 Σ( ° △ °|||)

The paleontologists found some fossils and on the basis of this discovery, they announced these dinosaurs were at least 25 million years older than any other similar type previously found in North America. Hence, these two actions are not independent of each other. There is a causal relationship here. Hence, presenting these two information as two independent entities in a parallel list does not make sense.

1.they指代不清，有歧义，指paleontologists还是fossils

2.比较对象不一致 fossils are older than types错❌，必须加 older than those of any similar dinosaur type

3.B，两个宾语从句错announced that……and they were……，后句应该和前句在一个宾从中
且they were at least 25 million years older than，陈述客观事实应该用现在时are

4.逗号问题，同位语前面肯定可以加逗号，ABC中，两个并列的句子加不加逗号 不知道……
Type前有any，用单数比较好
types that were previously，定从多余，直接previously found in North America简洁

fossils of some of the biggest armored dinosaurs ever found, fossils that are at least 25 million years older than those of any similar dinosaur type previously

结构：主句，同位语+定语从句

是同位语，但不是同位语从句。
同位语从句是：the fact that A do B。这里的that A do B叫同位语从句。
同位语是用一个名词来同位于另一个名词，甚至一个句子。例如
Trump, the president of USA, is a man.
这里的the president of USA就是Trump的同位语。同位语本身不要求抽象名词什么的。这道题目就相当于是一个这样的同位语，只不过名词身后还带了一个自己的定语从句罢了。