McKinnon was signed to a four-year deal worth $30 million on Wednesday while Richburg received a five-year, $47.5 million deal to join the 49ers.
As he said via a statement issued by the team on Wednesday, Lynch reaffirmed that McKinnon and Richburg were the 49ers' top two targets on their priority list.
"To land them, that's pretty special for us," he told the media.
Shanahan explained what made the two players the team's top priorities headed into free agency.
"It always starts with the tape for me, and these guys were as impressive as anyone at their position on tape. And then everything else goes to the type of people they are," he said.
The 49ers' starting running back last season, Carlos Hyde, has departed via free agency to the Cleveland Browns. McKinnon will be the team's featured back. Shanahan went on to explain in more detail what he saw in McKinnon that impressed him.
"When it comes to a running back, it starts with how they run the ball," he said. "I think he's an extremely good runner since college. It was hard to evaluate him in college because he was a quarterback, but he was a very good running quarterback. He could throw a little bit too, but I always knew he had running skills.
"Then to be able to study him on NFL film where he was actually at the running back position and to be able to see that he can make people miss, and he can create arm tackles, and he has the strength and the power to break those arm tackles.
"Then what is a huge bonus on him is when you talk about the pass game. When it comes to separating and beating linebackers and safeties in man-to-man coverage, I definitely think he's an issue for teams. I think this league, when it comes to third downs and things like that, you move the chains based off of matchups, which allows you to get points in the long run.
"I think Jerick is very versatile and we can do a lot of things with him."
Shanahan went on to discuss Richburg, who is the 49ers' undisputed starting center following the trade of Daniel Kilgore to the Miami Dolphins.
"When you have a center in our offense that can play at the level that Weston can, it gives a huge advantage," Shanahan said. "When you have guys who can read shades on their own, when you don't need the help of the guard, and things like that, the types of personnel groupings you can get into and stuff, it adds a lot to your offense.
"I've been around some real good [centers] in my career. He's put it all on tape, and he looks right there with all those guys. That's why I value him a ton off the tape. I didn't know a ton about him until I turned on the tape and it was as good as I've seen."
Shanahan went on to say that after looking at the tape, the team then looks into who the player is as a person.
"Everything we found out, just from his work ethic, everything that I say is very important to us, he's off the charts in those areas too," he said. "So I think he can add a lot of things to our run game, to our pass game, and make a lot of other guys' jobs easier as it is."
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