About 65.5 million years ago about 75% of all of Earth species became extinct, but obviously our ancestors survived or we wouldn’t be here. There were many more dinosaur-like species than there were mammalian ones, and because of their variety and numbers they were probably spread around the Earth into more ecological niches than mammals. Because of their widespread diffusion, it would seem more likely that some members of the dinosaur type in the various remote locales would survive and reestablish their dominance, but obviously again that didn’t happen or we wouldn’t be here and mammals would still be relatively rare.
What happened that permitted the mammals to survive the multi-month long sun-choking overcast that killed most green vegetation? All animals depend upon the sun, either directly by eating plants, or by eating animals that eat plants etc. Okay, for the quibblers, there are a few that live in mineral springs at the bottom of the ocean at the ridges, which may not have been much affected by the Chicxulub bolide impact which blasted up the cloud which blotted out the sun, which killed the plants, which starved the herbivorous animals, which starved the carnivorous ones.
The surface-dwelling animals living on the most available part of living plants above the surface would be the first to die because they would be most exposed to the quick die-off of the plants. But those animals which were forced to live underground and eat roots, and which lived in the high latitudes and hibernated much of the year would be the least dependent upon continuous sunshine. When the plants died from lack of sunshine, their roots would still be available for several years to the root-eating animals. Those living in the zones which have a long winter would be pre-adapted to long periods of little or no food, and the double length winter might have freed up food resources not usually available in normal winters.
Subarctic gophers and ground squirrels would fit this life pattern and would be much more likely to survive this Earth-darkening event better than any tropical animal. This scenario has appealed to me for years, but tonight on TV-NOVA – Mt. St. Helens Back from the Dead (#3710H) there was a program dedicated to the return of species to the slopes devestated by the eruption of 1980. The researchers were searching the miles of totally scorched and desolated volcanic debris and were shocked to find brown patches appearing on the side of the mountain. On closer inspection they found healthy gophers. These animals appeared on the surface even before vegetation appeared. It later appeared that the gophers themselves were bringing fresh seeds to the surface and restarted the plant communities. These animals were underground when the eruption killed everything and covered the surface with volcanic materials. But the gophers had survived because of their deep habitat. It would have been interesting to discover just how deeply the gophers had been buried and had to dig themselves out. In any case these mammals were the first sign of life after the eruption.
The Chicxulub extinction event might have been even easier for these animals to survive because the onset would have been slower. Instead of a few seconds or minutes to hurry deeper into their burrows, they would have had days or perhaps months. Apparently these subterranean communities can have miles of burrows, so their survival might not have been difficult.
While all else was devastation our distant ancestors’ homes were comfortable.