User blog comment:BannedLagiacrus/Discussion of the Week: Extinct and Unknown Status Monsters/@comment-5853890-20140606100051

Was going to say Wyvern Rex is my favorite right off the bat unitl I read Enshentosapent along with the info banned posted down below.

My guess is that they are rarely seen primarily because they live very deep in the ocean and only go to higher levels when food sources are low. So in theory, I say they are thriving but just rarely seen.

As for Ancient Lagi, my prediction is that it is still thriving. From the provided description from Bann, the glow could possibly indicate that it lives in dark underwater caves and most likely hunts on by luring and abmushing preys that are near their caves, same can be said for when hunting near land (much like how Plesoith does). I cannot say that it lives in deep ocean trenches where there is no light because it is stated to had attack ancient civilization. To avoid a long post, think about the Anglerfish (over whatever how you spell it).

If any ancient monster where to return, I say the better bet is to place in a MH game that is based on the past where the ancient and extinct species roam the land. Basically a pre-quel to the series.