No matter what order they are taken Thursday night, Ndamukong Suh and Gerald McCoy are set to make history.

If Detroit and Tampa Bay follow what most mock drafts suggest, McCoy and Suh will become the first pair of defensive tackles chosen among the top three picks since the AFL-NFL merger in 1970.

This is odd considering the long-standing importance and scarcity of interior defensive linemen. The 2010 free-agent market for nose tackles was stripped when three of them -- San Francisco's Aubrayo Franklin, New England's Vince Wilfork and Green Bay's Ryan Pickett - were designated as franchise players. Pittsburgh's Casey Hampton would have received the same tag if he hadn't re-signed in late February.

In recent years, some teams like the Browns (Shaun Rogers), Bills (Marcus Stroud) and Jets (Kris Jenkins) had to swing trades to address their needs. When an elite defensive tackle has hit the free-agent market, the price tag has been astronomical. Case in point: Albert Haynesworth landed what was essentially a four-year, $48 million contract in 2009 that includes $41 million guaranteed from Washington.

When I asked Lions coach Jim Schwartz why dominant defensive tackles are so difficult to find, he cited the "Planet Theory" previously espoused by Bill Parcells and late New York Giants general manager George Young.

"Big giant men that run fast, are strong enough to play the run and athletic enough to play the pass? There's not many people like that walking the planet," Schwartz said last month at the NFL owners meeting in Orlando. "Running backs can come in a lot of different shapes. Quarterbacks, wide receivers, tight ends, linebackers, corners, safeties -- good gracious, look at the (physical) difference in some of the safeties this year -- but the 300-pounders? You're not going to find the 250-pound defensive tackle."

Yet a defensive tackle hasn't been picked in the top three since Gerard Warren (Cleveland) in 2001. Before that, it was Dan "Big Daddy" Wilkinson by Cincinnati in 1994. In comparison, there were 17 quarterbacks, eight left tackles and seven defensive ends picked in the top three during that same span.

As the Black-Eyed Peas would sing, where is the love?

"Even though there is so much reported on quarterback being such a tough position to hit on, it's the same with defensive tackles," Atlanta Falcons general manager Thomas Dimitroff said. "It's no secret, there have been a lot taken early who have not lived up to expectations."

The NFL landscape is littered with such high-profile busts. Warren, who is currently a free agent after being released by Oakland, and the retired Wilkinson had long careers but never justified their lofty draft standing. Every other top six defensive tackle in the past decade - Glenn Dorsey, Dewayne Robertson, Jonathan Sullivan and Ryan Sims - also failed to meet expectations largely due to injury, laziness or a change of scheme by the team that drafted them.

These failings help explain why teams are hesitant to make such a heavy financial investment in such a boom-or-bust position.

"Year in and year out, we have learned that it's the position least likely to be balls-to-the-wall," one NFL general manager said. "It's two plays on, five off. That's the thing that scares people off. Am I going to get an 'every-play' guy or the flash guy?

"You're going to get that at the position because the guys are so big. When building your team, it's an uneasy feeling picking that. You're going to put $30 million guaranteed into this guy and draft him in the top two or three when you're not sure what you're getting?"

Such uncertainty is compounded by the position's nature. Most nose tackles and many 4-3 defensive tackles are removed in passing situations as opposed to quarterbacks and left tackles who are every-down players. In recent drafts, most teams have waited until the third round or beyond before investing in interior defensive linemen. The increasing number of teams using 3-4 defenses has made linebacker - especially outside pass-rushers -- a bigger priority in their front seven.

Quarterback also is usually a bigger need for a franchise choosing at the top of the draft like this year with St. Louis, which is likely to target Oklahoma's Sam Bradford at No. 1. Atlanta personnel director Les Snead had a conversation about this with then-Falcons assistant coach Emmitt Thomas when the team was debating whether to make Dorsey or quarterback Matt Ryan the No. 3 overall selection. The Falcons chose Ryan and addressed defensive tackle in the 2009 first round by picking Peria Jerry at No. 24.

"I remember saying, 'If the guy is a franchise QB, they win for you. Franchise three-techniques, nobody has ever won a Super Bowl with that guy,' " Snead said.

So what makes Suh and McCoy such hot commodities?

Some of it is circumstance. The Lions and Bucs drafted franchise quarterbacks last year in Matthew Stafford and Josh Freeman respectively. Both teams currently have gaping holes at defensive tackle.

Suh and McCoy also are the most appealing 4-3 defensive tackle prospects since Dorsey and New Orleans' Sedrick Ellis in 2008. Suh had such a strong senior season at Nebraska that he became the first defensive Heisman Trophy finalist in 12 years. Although he played in a different scheme and was surrounded by better talent at Oklahoma, McCoy also was a difference-maker as a junior in 2009. Plus, both players are lauded for their intelligence, leadership and work ethic, an especially important characteristic considering how many interior defensive linemen battle weight problems.

"Both those tackles are dominating guys and really impressive to sit down and talk to," said Rams coach Steve Spagnuolo, who extensively interviewed Suh and McCoy at their respective pro days. "I mean impressive to the point where you sit there and say, 'How can a guy this young be on top of it so well from a lot of different angles?' "

But while the Lions seem set to take Suh ahead of McCoy, Schwartz admits there is simply no way to predict whether both can avoid the same fate of their disappointing early first-round predecessors.

"Those guys are good motor players," Schwartz said. "But a lot of those other guys were the same way (in college)."