I think these mass extinctions are important evolutionary agents that help shake the system loose,
and because they open up large ammounts of ecological space, they probably do allow for greater
evolutionary inventiveness than might have been poetntially possible in a situation of a really crowded world.
麻烦老师详细剖析...greater evolutionary inventiveness than might have been poetntially possible...
没了解这部分比较结构。
这个比较结构貌似复杂，其实你可以把它化简，然后就是你见过的一个结构了。先看一个简单的例句：
Now with the help of the internet we can find more information than was posssible.
than从句省略了形式主语it和外置的that从句（真的主语）。补全后从句为：
than it was possible that we could find without the internet.
你的句子和这个简单的例句结构相同，只是than从句没用was表示过去的事实，而是用了might have been表示对过去状况的推断，但其结构还是相同的，即than+be+possible. than从句的形式主语it和外置的that主语从句省略了。
我觉得目前你一个人可以补全你的句子了。