How do you say §523恐竜は昔々ほんとうに存在した巨大な生きものです。恐竜が絶滅した理由についてはいろいろ言われていますが、どれも科学的には証明されていません。 in English?

Dinosaurs were huge creatures which truly existed a long, long time ago. Though the reasons why they became extinct are much talked about, none of them has scientifically proved to be correct.