这是一个多重复合句
第一层
条件状语从句:if that is the right interpretation, 如果那就是正确的解释
主句:it leaves the question of what evolved into the trilobites and their kind as mysterious as ever.
第二层
嵌套主句:it leaves the question of … 那么它就留下了……问题
嵌套介词宾语从句: what evolved into the trilobites and their kind as mysterious as ever. 什么进化为一如既往是难以解释的三叶虫及其同类
【注释】
leave the question 直译是“留下该问题,可以变通为“把该问题留在面前”或“提出了该问题”
as … as ever 是习惯用语,表示“永远(仍然、至今或空前)….
as mysterious as ever 是the trilobites and their kind 的后置定语,意思是“如同以往一样神秘的三叶虫及其同类”或“永远都无法解释的的三叶虫及其同类”
参考译文:然而如果那就是它的正确解释,那么它就提出了是什么东西进化为永远都难以解释的三叶虫及其同类的问题.