As he conducted the autopsy on the Cowboys’ 2012 season, owner and general manager Jerry Jones remained adamant he wouldn’t point to the team’s diminished health as an excuse for its shortfalls. “I know we had injuries, but the teams we’re playing had injuries,” Jones said in a January radio interview. Days after he made that comment, defensive coordinator Rob Ryan was axed. The fact that his unit lost five starters and two key role players didn’t seem to factor into Jones’ decision to fire the boisterous Ryan after the Cowboys allowed 359 offensive points — the 10th-highest total in the league. But there was no denying the slew of injuries impaired the defense’s performance at the same time it highlighted the lack of depth on a roster the Cowboys will try to enhance as they descend on Indianapolis this week for the NFL scouting combine. Nine of the 36 Cowboys deployed by Ryan on defense were acquired after the regular season began. Two, who had been out of the NFL before the Cowboys called, became starters as Ernie Sims replaced Sean Lee at inside linebacker, and Eric Frampton eventually plugged the safety spot Barry Church had filled before tearing his right Achilles tendon Sept. 23. But the Cowboys could have had more alternatives if a higher percentage of their draft picks selected in the 2008 and 2009 had developed into capable reserves. This past season only five of the 18 players chosen in those two years were on the team, and their contributions as backups were minimal. Running back Felix Jones failed to keep the ground attack moving when DeMarco Murray was out for six games with a sprained left foot. Cornerback Mike Jenkins, a starter who had been marginalized following a controversy-filled off-season, struggled when he was forced to play in the slot and was burned 50 percent of the time in 2012.