Exactly why it should be so remains, however, hotly debated.
Modern pearly nautiluses, whose relationship to ammonites is much debated, have a similar arrangement.
The details are still being debated, but the deal would involve a yearly quota of whale catches and would require whaling vessels to have international observers on board.
James Screen, a researcher at the University of Melbourne, Australia, who led the study, said: "The concept of Arctic sea ice having a tipping point is still hotly debated.
The merits of more fiscal stimulus have been fiercely debated inside the Obama administration.
It was considered a sign of progress that India's Parliament debated "population stabilization" this month after largely ignoring the issue for years.
The effects of the policy are debated, but for a leading Chinese demographer, the policy had postponed the arrival of the world population of 7 billion by at least five years.
On a recent day, passers-by debated whether to feed them carrots, scallions or rice.
This limits the proportion of renewables that can be absorbed into the grid - although the level of that ceiling is hotly debated.
I debated the question with Helen.
As such, this question is as old as SGML, the precursor of XML, and has been hotly debated with no universally accepted consensus.
The repatriation of artworks and antiquities is one ofthe most debated and controversial arguments in the art world.
Then, as now, the decline of educational standards was hotly debated.
Still others were "watershed issues" that were debated by the working group and resolved in ways that guided the evolution of the language.
They debated the issue pro and con.
They debated it in whispers.
