Question

the most important advancement of mammals over repltiles is

Answer 1

"Our results indicate that mammals are special," said study leader Michael Alfaro of UCLA.

The research allowed scientists to calculate for the first time which animal lineages have exceptional rates of success. The so-called "winners" have more species in their group, which means they have successfully evolved and diversified into many types of environments. The losers have diversified less, even over the course of millions of years.

The distinction doesn't imply that the losers are under a greater threat of extinction, however.  Even rich, diverse lineages include endangered species.