So much fun stuff, where to begin.
Regarding this graph, I see that the CO2 levels and temperatures were similar to those today. The proto-mammalian therapsids were evolving just fine until the big disaster, then Lystrosaurus held out for a time, and the dinosaurs/lizards ruled for 150 million years. Perhaps there is an important difference in mammalian style vs lizard style metabolism that caused the failure of the therapsid line, leaving only a few tiny proto-mammalians to hide in the bushes for all those years. Should this worry us today with increasing CO2?
As to why the dinosaurs did not survive the meteor event(s) of 65mya, a theory I have not heard is that it/they probably destroyed the ozone layer for quite some time. I can see the poor dinosaurs dying of skin cancer. Note the creatures that did survive. Birds covered with feathers, frogs and salamanders living in water or under plants and rocks, alligators living and resting in mud bank caves, mammals covered with fur and living in bushes.
A great book is "When Life Nearly Died: The Greatest Mass Extinction of All Time," by Michael J. Benton, 2003. There is an interesting graph on pg. 172 showing "radiometric ages, the carbon isotope curve, and the ranges of 333 species of fossils identified from 90 metres of rock in the Meishan quarries. A, B and C mark the three apparent pulses of extinction." These three pulses occurred over a million year spread, and could coincide with several boloid events.
For those who like the vulcanism explanation, see pg. 275 with "A summary diagram showing how the eruption of the Siberian Traps led to major atmospheric changes and to the collapse of most of life on Earth 251mya." [I would post these, but don't have the computer capability or knowledge.]
Regarding the idea of contrecoup damage, is this the same concept as when a bullet hits a skull it causes a small hole going in but a big hole or bulge on the opposite side of the head? If so, then this was my initial thought for the Yucatan/Deccan Traps situation, until I heard about the "Shiva Crater". There is a lot on google there. At the end Permian, all the land masses were pretty much stuck together as Pangea. I think that the Bedout and Antarctic Craters would have been toward the south end, and the Siberian Traps toward the north end, but I am not sure there would have been enough oppositeness for a ballistic type effect. That is why I think there may be a crater hidden under the Traps.
Close. Not a bullet, but blunt (non-penetrating) trauma. The medical condition is caused by the brain bouncing off the opposite side of the skull from the impact.
In this case imagine you are standing at the antipodes of a major impact. The shock-wave travels through the surface rocks in a a wave like the ripples from a stone in a pool, except the earth isn't flat! At some point the shock waves have traveled half way around the world, to where you are standing. They come at you simultaneously from all points of the compass, and as the leading edge of the shock-waves go from a full planet's diameter at the quarter way around point, they are re-compressed and concentrated to that little bit of land you are standing on.
This refocusing dumps a goodly fraction of the energy of the impact into a small area. as the rock gets slapped from all sides at the same time it crushes and shatters. The energy gets squirted down into the mantle, and up into space.
Not that you get to appreciate the ride, because somewhere along the way (in the first few milliseconds or so) the bottoms of you feet have been driven through the top of your skull...
There would be remote damage where the shock waves from the impact met and reinforced each other. On a perfect sphere of consisting density the shock waves should meet and reinforce at the antipodal location. Earth is not a perfect sphere and is not of consistent density so the shock waves would not necessarily reinforce at the exact antipode.
The Siberian area may have already had a working hot spot (as the Deccan Traps had) or a weakened structure so that the Antarctic impactor either triggered or exacerbated the Siberian volcanism.
The Shiva crater theory is not widely accepted.
This does seem to be what may have happened 17 mya when an impactor struck SE Oregon causing the volcanism that created the Snake River and Columbia Basalts and the hot spot that has now migrated to under Yellowstone Park.
There seem to be periods when impacts occurred for a while; also, impact ejecta would spread the fun around to some extent -- the larger the impact, the worse the damage from the ejecta. Nice post.