For example, some have blamed dinosaur extinction on the development of flowering plants, which were supposedly more difficult to digest and could have caused constipation or indigestion — except that flowering plants first evolved in the Early Cretaceous, about 60 million years before the dinosaurs died out.

　　结构分析：

　　复合句，带有which引导的定语从句， except that引导的条件状语从句，以及before引导的时间状语从句。

　　句子分析：

　　some have blamed dinosaur extinction on the development of flowering plants，主句中some主语，have blamed 谓语，dinosaur extinction宾语，on the development of flowering plants 宾语。本部分意思：例如一些人将恐龙灭绝归咎于开花植物的发展。

　　which were supposedly more difficult to digest and could have caused constipation or indigestion 定语从句修饰plants，which为主语，系表结构 were supposedly more difficult to digest，与动宾结构 could have caused constipation or indigestion作并列谓语。 本部分意思是据说这些植物更难消化，可能导致便秘或消化不良。

　　except that flowering plants first evolved in the Early Cretaceous, about 60 million years before the dinosaurs died out 条件状语从句中，flowering plants 主语， evolved 谓语， in the Early Cretaceous 时间状语 , about 60 million years 定语，修饰the Early Cretaceous。before the dinosaurs died out，时间状语从句中，the dinosaurs 作主语，died out 谓语。本部分意思是：除非开花植物在早白垩纪，恐龙灭绝前的大约6000万年前，就已经开始进化。

　　参考翻译：

　　例如一些人将恐龙灭绝归咎于开花植物的发展，据说这些植物更难消化，可能导致便秘或消化不良，除非开花植物在早白垩纪，恐龙灭绝前的大约6000万年前，就已经开始进化。