From the Voteview blog:
Even over an 18-year period, there has been so much movement of both the 10th and 90th conservative percentile House Republicans away from the center that the current 10th percentile Republican would have been near the median Republican in the 104th Congress during the last protracted shutdown.
Thad Hall has a lot more detail on the same issue over at Mischiefs of Faction:
The bottom line here is simple: The Republican Caucus has become more conservative since just the last Congress.