Use of past perfect continuous in the following sentence

Hi,

I found the following sentence as an example that illustrates the use of past perfect continuous tense:

The dinosaur had been dominating the earth's biome for almost three million years when it became extinct some 67 million years ago.

I also read that past perfect continuous tense refers to an action that started at a given past time and continued till another past time and was in progress at the second past time. So in the above sentence when we say that dinosaurs became extinct some 67 millions years ago, it does not convey the meaning that dinosaurs were dominating the earth's biome at that time. Can you correct me if I am wrong? Is the above example correct illustration of past perfect tense?

Thanks,
Richards.