Draft pick signings
First, the Dolphins signed three more of their draft picks to contracts on May 19. Sixth-round running back Jalen Parmele, sixth-round running back Lex Hilliard and seventh-round

Matt Spanos signing
The Dolphins also added yet another undrafted free agent, signing former USC center Matt Spanos.
Spanos (6-4, 300) was the USC's starting center in 2007 after Ryan Kalil graduated the year before. He appeared in 10 games (nine starts) for the Trojans this past season, missing the team's first three games with a triceps injury. For his efforts as a senior, he was an All-Pac-10 honorable mention.
Prior to his senior season, Spanos played in a reserve role for the Trojans and worked at every offensive line position. He redshirted in 2003, was a backup offensive tackle in 2004, a backup center in 2005 and worked at guard in 2006 before becoming academically ineligible.
Spanos will wear No. 75 and will compete for a reserve offensive line role. The signing currently gives the Dolphins 16 undrafted rookies, including four offensive lineman.
Analysis

Both he and fellow undrafted center Mike Byrne (Delaware) have the versatility to play all across the offensive line, so there's no clear-cut advantage there. One has to assume that when it comes to competition faced, the edge goes to Spanos having played at USC.
Nevertheless, Spanos will have his hands full, and it's entirely possible that even if Steve McKinney wins a starting guard job, the team will only keep eight or nine lineman and opt to use McKinney as a possible center backup.