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…)

　　翻译：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中嵌套着分句2.

　　分句2是of结构作后置定语修饰说明question的内容。