SAN JOSE -- The center position was an ever-evolving area of the Sharks' game during the 2018-19 season, with its highs, lows and changes in personnel. 

The team had added depth this past season with Joe Thornton moving to third-line center and with Tomas Hertl's successful transition to the pivot partway through the season. But San Jose also had difficulty finding a regular winning combination for its fourth line, and at the end of the regular season, it was ranked 15th in the NHL with a 50.3 faceoff win percentage -- and its four best skaters in the faceoff circle all spent the majority of their seasons playing on the wing.

Given the Sharks had some serious questions to answer involving the center position after Chris Tierney was sent to the Senators in the Erik Karlsson trade before the season started, San Jose ended the season with decent depth down the middle. Looking ahead to next season, however, there is room to grow -- and a couple more questions that need to be answered.

The Sharks' top lines are pretty much set, with Hertl and Logan Couture centering them. Couture has been a staple down the middle for San Jose for some time now, and his work over the past season with Timo Meier on his wing gave the Sharks an opportunity to score goals on a nightly basis.

Hertl's arrival as a key center for the team was more of a surprise, as he continued to build his game as a power forward after coach Peter DeBoer put him at the pivot before the turn of the new year. Hertl continued to grow in the position as the Sharks made a 20-game playoff run, taking over responsibilities with captain Joe Pavelski out of the lineup. Hertl went 56.2 percent in the faceoff circle during the playoffs, and played with a broken pinkie finger. Just imagine how much he can improve now that his finger is fixed.

San Jose's bottom lines are a bit of a different story, though, especially if Thornton doesn't return next season. Either way, there still will be an unofficial tryout to see who will best fill in that center role.

While Barclay Goodrow spent a chunk of the past season in that position, it seems very likely Dylan Gambrell will get a good look after spending last season bouncing between the AHL Barracuda and the NHL club. Of course, that's dependent on the Sharks signing the restricted free agent this summer, although that seems like a strong possibility.

If fellow center and RFA Antti Suomela still is around next season, he also could get a look, much like he did on the third line at the start of this past season. Another RFA on San Jose's long free agent list is Rourke Chartier, who began the season centering the fourth line while Thornton was dealing with complications involving his surgically repaired knee. However, injuries hampered Chartier's playing time at the AHL level this past season, and his future with the team remains a mystery. 

One player we didn't see up at the NHL level over the 2018-19 season was Alexander True. The young Danish center is coming off a team-leading 55-point campaign with the Barracuda, and he could get a look with the big club when training camp gets underway.

[RELATED: Couture could finish as top goal scorer in Cup playoffs]

Again, the Sharks might look to add another center to the mix if Thornton doesn't return next season -- and even more so if Pavelski goes to a different team. Even if San Jose makes a deal to keep gritty forward Micheal Haley, that still leaves the Sharks with a lack of skill down the center of their lineup.

In addition to centers from the Barracuda receiving a look, there's a chance the Sharks could make a trade for a more skilled player to help fill that void. San Jose also could add a center or two in this year's draft, although that likely wouldn't have an impact on the big club until after this next season.

Editor's Note: For having only existed as an NHL franchise for 27 seasons, the Sharks sure have been involved in a seemingly inordinate number of headline-stealing trades. Some of the greatest players in San Jose franchise history have been acquired via trade, and each has inevitably played a major role in the successful evolution from expansion team to perennial cup contender. This week, NBC Sports California will look back at the five most important trades in Sharks franchise history, beginning with the trade for Owen Nolan.

Like most expansion franchises, the Sharks weren't very good their first handful of seasons in the NHL. After debuting in 1991-92, San Jose reeled off back-to-back last-place finishes in the conference in its first two years of existence. The next two years, the Sharks qualified for the postseason, but lacked the kind of high-end talent to pose a significant threat (don't tell that to the 1993-94 Red Wings).

San Jose went winless over the first 11 games of the 1995-96 season, in what would lay the groundwork for Kevin Constantine's dismissal as head coach. But after the seventh consecutive non-victory to begin the season, the Sharks made one of the most important trades in franchise history that would eventually help establish the perennial playoff team we've come to know today.

On Oct. 26, 1995, San Jose traded defenseman Sandis Ozolinsh to the Colorado Avalanche in exchange for winger Owen Nolan, and the Sharks franchise was changed forever.

The trade didn't reap immediate benefits, mind you, at least not for San Jose. The Sharks would go on to a last-place finish that season, over which Nolan tallied a team-leading 29 goals in 72 games. The Avalanche, meanwhile, went on to win their first-ever Stanley Cup, with Ozolinsh contributing 50 points from the blue line.

It wasn't a trade for the now, though. It was about the future.

The next season, San Jose improved by seven victories, and Nolan led the Sharks with 31 goals and 63 points over 72 games, not including his called-shot against Dominik Hasek in the 1997 All-Star Game, for which San Jose was the host. Since that season, the Sharks have missed the playoffs a grand total of two times.

Owen Nolan calls his shot against Hasek 1997 All Star Game pic.twitter.com/5XxcJdJgPl

— Classic NHL Clips (@90sNHL) February 8, 2019

While Nolan's numbers weren't as prolific in 1997-98, he ranked second on the team in scoring and led San Jose to a postseason berth. Heading into the next season, Nolan was named the seventh captain in franchise history. Then, during the 1999-00 season, everything clicked.

Playing on a line with recently-acquired center Vincent Damphousse and speedster Jeff Friesen, Nolan experienced the best season of his career, tallying a career-high 44 goals, 40 assists and 84 points in leading the Sharks to an eighth-place regular-season finish in the Western Conference. That pitted them against the President's Trophy-winning St. Louis Blues in the first round, a series most pundits expected to be a sweep at San Jose's expense.

The pundits, of course, were wrong, and Nolan had plenty to do with it.

After dropping the first game in St. Louis, the Sharks won the next three games of the series to put the top seed on the brink, but the Blues battled back to force a Game 7 back at their home barn. Fourth-line winger Ron Stern -- he of four regular-season goals that year -- scored less than three minutes into the game to give San Jose an early lead, one the Sharks would maintain throughout the entire first period. But just before that period came to an end, Nolan scored one of the most memorable goals in franchise history while simultaneously dealing a crushing blow to St. Louis' hopes.

With just over 10 seconds remaining in the opening period, Nolan launched a blistering slap shot from just across center ice. The high, driving shot snuck through Blues netminder Roman Turek, sending the San Jose bench into pandemonium. Friesen made it 3-0 less than six minutes into the second, and St. Louis was officially done for.

[RELATED: NHL Network ranks two Sharks among top four defensemen]

Nolan totaled 115 points in 132 games over the next two regular seasons, the first two 40-win seasons in franchise history. San Jose then took a step back in 2002-03, and Nolan was traded to Toronto late in the season. Despite the lackluster conclusion to his Sharks' career, Nolan is celebrated as one of the greatest players in franchise history, still ranking in the top six in goals (206), assists (245), points (451) and penalty minutes (934).

Everyone knows the Sharks have some of the best defensemen in the NHL, but depending on who you ask, that might not be giving them enough credit.

Last week, NHL Network ranked the top-20 NHL defensemen heading into next season, and let's just say San Jose was well represented.

Some serious star power on that list 🌟#NHLTopPlayers pic.twitter.com/YIjc5xqTYL

— NHL Network (@NHLNetwork) August 19, 2019

That's right. According to the league network, the Sharks not only have the best defenseman in the NHL, but two of the best four overall. The rankings seem pretty darn accurate, considering each of Brent Burns, Victor Hedman, Mark Giordano and Erik Karlsson are all former or current Norris Trophy winners.

Giordano won the award this past season after tallying 17 goals and 57 assists for the division-winning Flames. But it was Burns (16 goals, 67 assists) who led all NHL defensemen last season with a career-best 83 points.

#88 in your program, #1 on our list!

Do you agree that @Burnzie88 is the best defenseman in the @NHL Right Now?#NHLTopPlayers | @SanJoseSharks pic.twitter.com/kcCSXie4zR

— NHL Network (@NHLNetwork) August 19, 2019

"He's big, he's gnarly, he's a guy that is a dynamic player that changes the game in a split second," NHL Network's Ken Daneyko said of Burns. "He's such a beast, and when he's playing physical as well -- and you see that at times -- he's a menace out there."

Karlsson was acquired in a trade with Ottawa just prior to the start of the regular season, and could have given Burns a run for his point-leading money had he not been severely hampered by a nagging groin injury throughout the year. For segments of the regular season, though, including arguably the Sharks' best stretch in which they won 16 of 21 games starting in early December, he was undoubtedly their best player.

"Probably the best offensive defenseman, for my estimation, in the national hockey league," Daneyko said of Karlsson, whom he expects to have an even better season next year now that he's acclimated and, hopefully, healthy.

NHL Network posed the same question to fans, and, well, they had a slightly lower opinion of both of San Jose's star defensemen.

Let's see how YOU rank the Top 20 Defensemen Right Now...#NHLTopPlayers pic.twitter.com/hvt4mwS3IC

— NHL Network (@NHLNetwork) August 19, 2019

[RELATED: Could Sharks lose big-name D-man to Seattle in expansion?]

There's a lot of great defensemen on that list and all of them should feel honored to be listed among them. We're going to go out on a limb and assume the Sharks are feeling pretty good about the status of their back end.