So the fact that nowadays the mutation the team have discovered affects only the pectoral fin does not rule out the possibility of （its having also stimulated） ,way back then,the arrival in the pelvic fin of the fishy progenitor of the mice,（of the bones） now known as the fibula and tibia.
括号里面有点看不懂
最后一句的of the bones，是不是应该和前面的pelvic fin连一起看，就是(pelvic fin)of the bones指骨头的达骨盆鳍
还有就是its having also stimulated，为什么用its having不用 it has
括号里面有点看不懂
最后一句的of the bones，是不是应该和前面的pelvic fin连一起看，就是(pelvic fin)of the bones指骨头的达骨盆鳍
还有就是its having also stimulated，为什么用its having不用 it has
