7.But these factors do not account for the interesting question of how there came to be such a concentration of pregnant ichthyosaurs in a particular place very close to their time of giving birth．

(Of结构作定语：of how there came to be such a concentration of pregnant ichthyosaurs…)

但这些因素并不能解释这个有趣的问题：为何在一个特定的地点会如此集中地出现即将临产的怀孕鱼龙群。

分句1：But these factors do not account for the interesting question

分句2：of how there came to be such a concentration of pregnant ichthyosaurs in a particular place very close to their time of giving birth

分句1嵌套分句2.分句2是Of结构作后置定语修饰说明question的内容。