Were almost all T. rex individuals wiped out at once?

[Vladimír Socha]

Good day!

I am curious about the proposed mass killing scenario for the majority of Laramidian dinosaurs shortly after the K-Pg impact. According to some sources, at least 2400 km from the Chicxulub crater rim, everything burned and/or was destroyed by the shockwave, expanding impact plume, hurricane-force winds, IR radiation from the impact spherules returning to the lower layers of the atmosphere etc. We know for sure that there was a southern population of T. rex in what is now Colorado, about 1700 (?) km from the crater, maybe even some 1200 (?) km in what is now Texas-Mexico border.* These would be probably killed almost instantaneously. But even in what is now Saskatchewan and Alberta in Canada, over 3000 km away from the "ground zero", there were still hot winds exceeding speeds of 100 kph, lethal IR radiation and perhaps widespread wildfires. Is it hence plausible to say that even if some T. rex individuals (esp. small juveniles) were able to find some kind of a cover and survived, they were functionally extinct even before the arrival of the impact winter? According to some estimates, there were about 20 000 sexually mature individuals of a T. rex at any given time of their existence, so I wonder, how many of these were killed or injured on the very first day of the Cenozoic? Thank you for your thoughts! VS.

* According to Mark P. Witton's book King Tyrant (2025).

References:

Robertson, D. S.; et al. (2004). Survival in the first hours of the Cenozoic (PDF). Geological Society of America Bulletin. 116 (5–6): 760–768.

Robertson, D. S.; et al. (2013). K/Pg extinction: Re-evaluation of the heat/fire hypothesis. Journal of Geophysical Research. 118 (1): 329–336.

Brugger, J.; Feulner, G.; Petri, S. (2016). Baby, it's cold outside: Climate model simulations of the effects of the asteroid impact at the end of the Cretaceous (PDF). Geophysical Research Letters. 44 (1): 419–427.

Morgan, J. V.; et al. (2022). The Chicxulub impact and its environmental consequences. Nature Reviews Earth & Environment. 3 (5): 338–354.

Marshall, C. R.; et al. (2022). With what precision can the population size of Tyrannosaurus rex be estimated? A reply to Meiri. Frontiers of Biogeography. 14 (2).

Senel, C. B.; et al. (2023). Chicxulub impact winter sustained by fine silicate dust. Nature Geoscience. 16 (11): 1033–1040.

[Russell Engelman]

It's possible that some survived, but from a practical standpoint so many of these would have died from the initial aftermath of the extinction their survival may as well be measurement error relative to the impact. The collapse of terrestrial food webs would mean a rapid decrease in the large herbivore population, with the carnivores following due to lack of food. I've seen estimates suggesting that photosynthesis didn't start up again after the impact on the order of years. For reference, the eruption of Mount Tambora in 1815 which was a fraction of the magnitude of the impact and provided much less blockage out the sun for only a year caused widespread crop failures and famines. Not to mention North America seems to have suffered more from the impact than any other landmass. While new fossils could always prove us wrong, right now it seems like any survival of Tyrannosaurus past the boundary was probably a blip.

There's an old sci-fi novel called Cretaceous Sea (2002, Will Hubbell) that I think has one of the best depictions of the K-Pg impact. It really helps the reader visualize just how desperate the situation was by letting us see it through the eyes of a set of human time travellers stranded by it. The impact itself wipes out most of the dinosaurs, with only a scattered few surviving. The big herbivores die off first due to lack of access to food. Tyrannosaurs survive a little bit longer due to access to all the carrion, but eventually they end up weakening and starving to death. Some small thescelosaurs also survive a bit, but they end up dying off as well. Eventually it's just the protagonists and a bunch of Troodon (with feathers!) feeding on hibernating mammals and scraps of carrion, and even the Troodon appear to be dying off. It's very clear the protagonists would have died there without the deus ex machina of godlike future Buddha babies getting involved.