[MUDDOG]

kill all these animals at once... something happened, something so major .... probably something as simple as a slight change in chemicals or oxygen or CO2 level

I doubt that a slight change in atmospheric CO2 would cause an immediate mass die-off.

Maybe his funding would die off if he didn't say that.

[UCANSEE2]

Some volcanic vents leaking out of a nearby lake, producing a layer of poisonous gas for miles around would do this. There are areas like that currently. There were likely many more way back then.

[Trumpet 1]

A fire storm from a gigantic falling meteor and its impact. The one 65 million years ago that hit the Yucatan Penninsula wiped out 90% of all life forms on Earth. Some smaller ones could cause local damage. Himalayan mountain range was the result of the big one from 65 million years ago. The entire Earth’s crust went liquid for about 2 seconds. And of course there is always moltan lava and gasses.