It's "studies" like this that give Creationist ammo against all science
You would think the authors would have at the very least check when exactly these animals actually went extinct before proclaiming that a comet wiped them out 1000's of years before they really did die out.
If it makes anyone feel any better, this scenario — which involves bombardment of the Earth by various waves of particles and objects, different sizes and energies, with the waves separated by either hundreds or thousands of years, and originating in a relatively nearby star which went kaboom —
More and more Epicycles!!!!!!!!! 
is catching on some, but, as with the Alvarez model for dino extinction via an impact at the K-T boundary, has met with furious resistance.
Megafaunal extinctions followed human arrival in Australia, North America, New Guinea, Madagascar and South America.
Now which makes more sense?
A) Human predation and maybe diseases slowly drove these species to extinction
or
B) Coincidentally, where ever humans arrived, comets/asteroids then began to hit where these new humans were and over 100 to 1000s of years they bombarded the area, leaving no trace, but they somehow killed one or two species off at a time (while apparently leaving the others unscathed) until they were all gone.