句子：Because they had more advanced techniques than were available to earlier researchers, the archaeologists also were able to identify actual plant  remains - micro-fossils in the soil from banana plants, and also grains of starch from taro, on the edges of stone tools that date from about 10,000 years ago.

请问老师：than后面省略的主语是什么，是techniques吗？如果是techniques，techniques在主句部分是宾语，但是在从句部分又成了主语，这样不是对等成分的比较，可以成立吗？怎么理解呢？