For so long the towering O's were imperious and immovable.
Whether it was O'Kelly, O'Callaghan or O'Connell, Ireland ruled the skies for a decade with confidence, soaring with the impressive elegance of a green-liveried Aer Lingus bird.
Now, O'Kelly is gone; O'Callaghan is at the veteran status; O'Connell's future fitness is in a realm where even science cannot offer certainty in response.
In their stead, a new partnership has combined as twin towers; typically, given the extensive reign of the long-standing institutions they are replacing, Donnacha Ryan and Mike McCarthy do so nearer 30 than 20.
That maturity may be an asset – neither man is learning on the job.
McCarthy has maintained his high provincial performance levels when transferred to Irish green. Ryan was Ireland's best performer on the surreal summer tour to New Zealand. Together, they seem to click.
"He's great," said Ryan of his English-born partner, who turns 30 this Tuesday. "I'd be a big fan of Mike. I've played with him for a good while now, with the As and stuff like that.
"He's a very robust type of fella, very physical and I love playing alongside him. He's great craic as well, unbelievable humour.
"I suppose, at this level, we've only played together just the once, so we're trying to build a good relationship with one another.
"And the more time we spend together as regards the set-piece and around the park we can get this good relationship going."
Ryan may be the more experienced of the pair, but of his 22 caps, only nine have been from the first whistle. Five-times capped McCarthy is convinced of Ryan's ability as the duo aim to establish an enduring partnership.
"We get along great and I'm learning a lot from him. I'm really excited about how the partnership is developing recently and I just hope it can continue," said McCarthy.
Ryan, so often used to toiling in the shadows of the O's in Munster – and Mick O'Driscoll, too – will handle Ireland's line-out today.
"Yeah, they're my calls, to the best of my ability anyway," he said.
"I only had the opportunity calling line-outs in the Six Nations when Paul left and then on the summer tour.
"I wouldn't have normally got to call line-outs with Munster because Paul is there and then Mick would have predominantly done it.
"Obviously, it's more work on the video and basically learn an awful lot more on the training park and on the field, because it's a skill in itself, trying to learn how to defend other teams. It just boils down to experience. When you lose one, I find the main thing is not to panic.
"You can get a bit flustered because they're all so big and they seem to cover everywhere, but if you just relax and stay cool a small bit, you'd be surprised where you'd find a bit of space.
"At this level getting the ball at the line-out is paramount. You want the ideal ball playing at the tail of the line-out all of the time, but that obviously doesn't happen.
"So you just have to make sure that you win the ball first and after that anything's a bonus."
An attitude both men have translated to their belated, but blooming international careers.