How Birds Survived when Dinosaurs Died

[taiwan_girl]

I have read that birds are the closest "relatives" to dinosaurs.

https://www.scientificamerican.com/article/an-asteroid-extinguished-all-the-dinosaurs-except-for-birds-heres-why/

Why did birds persevere when every single other type of dinosaur died? Scientists have puzzled over this question for decades. The mystery has deepened in the past 30 years as paleontologists have uncovered scores of feathery and winged dinosaurs that were closely related to birds and similar in many aspects of biology and behavior, though not actually part of the avian lineage. Some of these dinosaurs could even fly. What, then, allowed birds alone to escape the fate of their family?

Recently an answer has emerged, based on new research into fossils, genetics and ecology. Many birds were flying over the heads of T. rex and Triceratops when the asteroid hit, and most died alongside their dinosaur cousins. The only birds to make it out of the Cretaceous were modern-style species. Their survival came down to circumstance: where they happened to live and the features they happened to possess served them in good stead when the world went to hell.

and

Recent studies by Field, Derek Larson of the University of Toronto and their colleagues suggest that two factors were critical: habitat and diet. Where you lived and what you ate might have dictated your fate at the end of the Cretaceous. Crown-group birds had the winning combos.

Let’s consider habitat first. The effects of the asteroid touched all corners of Earth, but no environment had it worse than forests. They were pummeled, first by shock waves near the impact zone and then globally by fires and acid rain over the following days and weeks. Any trees that survived the onslaught would have been slowly starved of the sunlight they needed to photosynthesize their food. A plague of fungi preserved in the fossil record marks the mass die-off of forests. It probably took hundreds of years for them to grow back once the sunlight returned.

All animals that frequented trees would have been in trouble—their shelter, nesting grounds and food sources would have disappeared. Many Cretaceous birds, particularly the archaic long-tailed species, were tree-living specialists. But not Vegavis, Asteriornis, and other early crown-group birds, which lived around the water and on the ground. Their homes would have been damaged but not destroyed.

Now on to diet. When the long winter descended, ecosystems built on a foundation of photosynthesizing plants collapsed. When the plants died, plant-eating animals had no food, so they also died. Then the meat eaters succumbed, with the losses cascading up the food chain until the entire network went kaput. But one plant resource remained available for those that could take advantage of it: seeds.

Most plants would have died quickly, and animals that ate leaves, stems, shoots, fruits, or other parts of a growing plant were out of luck. Not so with seeds. As we see in modern-day disasters, seeds can remain viable in the soil for decades and allow ecosystems to return after a fire or volcanic eruption. Because crown-group birds had sharp, mobile nutcracker beaks, they would have been able to exploit seeds as food, whereas most other animals—including the archaic toothed birds—could not.

When you add it all together, survivorship at the end-Cretaceous meant winning an unhinged game of poker. Each species sat at the proverbial table with a hand of cards: where they lived, what they ate, how they grew and behaved. But the deck was frozen—they couldn’t draw any new cards, because there was no time to adapt through the usual processes of natural selection, of genes shaping success over the generations.
Instead the rules of the game were simple but brutal: What hand did you hold when the calamity struck? If you were slow-growing, unable to burrow or shelter, lived in the trees or had to eat a lot of food (especially plants), then game over. The nonavian dinosaurs, including most feathered dinosaurs, found themselves in this situation despite their resounding dominance over the previous 150 million years. So, too, did many bona fide flapping, flying birds.

But if you grew fast, could shelter or fly away from danger, lived on the ground or in the water, and could eat seeds, then any of those assets would have been beneficial and improved your odds at the poker table. And if you held all of those cards? You had a royal flush. Crown-group birds just so happened to hold this hand, and they won the game—and with it the opportunity to evade extinction, live another day and spawn a new dynasty of dinosaurs.