英语好的朋友帮忙看看这段英文i though the discussion was of average sized s

英语好的朋友帮忙看看这段英文
i though the discussion was of average sized specimens,not record weights?.likewise,only the siberian tiger has the edge in the largest captive specimens,that of the lion being greater than that of the bengal,and,in the case of the siberian,only by a slight margin.
这段是口语没看明白,请问最后一句only by a slight margin说的是谁比谁体重有微弱优势?是狮子比西伯利亚虎有微弱体重优势?还是西伯利亚虎比狮子有微弱体重优势?