BY FRED SEITZ
I have been somewhat remiss in keeping my bird feeders filled over the past several months. But when I have ventured into my backyard to replenish them, I’ve been closely monitored and followed by local birds. They were likely reluctant to have me encroach on their territory and potentially interfere with their other dining opportunities.
During these close encounters, I’ve contemplated my backyard birds’ ancestry and wondered if they were echoing some of their ancestors’ behaviors and traditions. And I’ve found it difficult to imagine how swallows, wrens and even pigeons evolved from some of the larger theropods, a group of carnivorous dinosaurs that includes Tyrannosaurus Rex. There is a growing scientific consensus that our feathered friends are, in fact, theropod dinos of a kind.
Theropods (literally, “beast footed”) are thought to have evolved about 230 million years ago. They walked on two legs, and each foot had three thin main toes, as our modern birds’ feet do. All meat-eating dinos were theropods.
Apparently, some birds that we think of as modern — birds possessing features like toothless beaks and fused foot bones — shared the planet with Mr. Rex when he was hunting down his more land-bound neighbors. A 2020 article in Nature magazine described fossil remains of Asteriornis maastrichtensis that showed a combination of modern waterfowl and landfowl features. (“It’s like a turducken,” a paleontologist told Science News.) The remains were almost 67 million years old, which means that this modern-type bird would have lived during T. rex’s short reign. Asteriornis is now considered to be the oldest modern bird.
- rex and his non-avian dino cronies departed the scene about 65 million years ago when that rude asteroid struck the earth, kicking up enormous clouds of ash and other debris, obscuring sunlight and changing the environment to something that Mr. Rex couldn’t handle. In contrast, many of his avian contemporaries survived and went on to evolve and thrive. Earth is now home to more than 10,000 species of birds.
Birds had several advantages over that short-armed reptile and his ilk. They had much lighter bones and could fly to more hospitable living places, thus enhancing their chances of survival. Their diets, which included seeds and insects, were more diverse. With pointy beaks, they could even crack open nuts.
Although picturing a T. rex garbed in feathers is challenging (and rather humorous), characteristics of the feathered, gliding Archaeopteryx speak to the evolution that brought us the birds we know today.
Archaeopteryx lived about 150 million years ago. About the size of a crow, it had well-developed teeth and a long tail; its three fingers, with sharp, curving claws, moved independently, like other more reptilian dinosaurs of its day. Unlike those dinos, though, it had feathers and wings, like a bird.
Part of the transition and miniaturization from large reptilian dino to birds was likely facilitated by the widely varying characteristics of the dinos themselves. That not-so-cuddly Velociraptor, who has terrified us in films, was also an ancient predecessor of the cute birds at our feeders. He’s thought to have evolved about 65 to 100 million years ago. About the size of a turkey, Velociraptor was more diminutive in size than many of his reptilian contemporaries. It had feathers but couldn’t fly.
Paedomorphosis, which is the retention of juvenile characteristics into adulthood, may have helped dinosaurs become smaller, over time, so they could inhabit more diverse habitats. Some of these evolutionary changes likely occurred during the embryonic stages of development and were retained.
While I enjoy feeding the birds in my backyard and contemplating the habits of their evolutionary predecessors, I’m grateful that dinosaurs now exist only in their current avian form. When I see a certain gleam in their eyes, though, I know to make my offering and leave them to it — watching from a safe and respectful distance.
