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If you were asked to close your eyes and picture a dinosaur, what would come to mind? Would it be the powerful Tyrannosaurus, or maybe the heavily-horned Triceratops?
What about a seagull or a woodpecker? Although long-extinct dinosaurs are what have fueled our fascination for films like Jurassic Park or books like Journey to the Center of the Earth, the birds that live among us today are avian dinosaurs.
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What is the origin of birds?
In 1861, a single fossilized feather was found in a slab of limestone in Solnhofen, Germany. Although it may sound simple, this was no ordinary fossil. It was found in a layer of rock that was 150 million years old, much older than when scientists thought feathers first appeared. That is why paleontologist Christian Erich Hermann von Meyer, who was asked to examine the fossil, thought it was a fake! Little did he know that he was holding a piece of the earliest bird-like dinosaur. The animal that bore this feather all those millions of years ago was named Archaeopteryx, meaning “old wing.” Archaeopteryx is now considered a link between two-legged dinosaurs and modern birds.
We have learned so much about Archaeopteryx over the past 160 years. It weighed about two pounds and was the size of the common raven (Corvus corax). Unlike modern birds, Archaeopteryx had teeth instead of a beak. It had a very long tail for its reptilian body, which was covered in black feathers. This early bird had strong enough wings to be able to fly in short flapping bursts. It had claws on the ends of its wings that may have been used to climb trees.
Why did feathers first appear?
Did feathers first evolve to help birds fly? If so, then why are some birds not able to fly? Other dinosaur fossil discoveries have shown that non-avian dinosaurs had feathers 100 million years before Archaeopteryx existed. Since flying birds showed up much later than the first feathers, scientists agree that feathers did not evolve specifically for flight. Instead, many scientists believe feathers helped to control the dinosaurs’ body temperature. This is similar to the way hair and fur help to warm up or cool down the bodies of mammals. Other scientists claim that the most important role of the first feathers, which may have been very colorful, was to attract mates.
Different opinions among scientists are important for learning and discovery. With the help of advancing technologies, new research constantly builds upon the findings from the past. Perhaps you could be the next scientist to help us learn more about the purpose of the first feathers 250 million years ago!
How did birds start to fly?
The evolution of flight was an incredible moment in the history of avian dinosaurs. Being airborne opened up many resources that were once unreachable in the highest treetops, like food, nests, and hiding spots from predators. Although Archaeopteryx was able to fly in short bursts, these animals were not capable of powered flight, which appeared later in bird evolution. You would not see Archaeopteryx soaring above your head like a falcon, or migrating long distances like an Arctic tern. Scientists have proposed three main hypotheses for the evolution of powered flight: trees-down, ground-up, and wing-assisted incline running.
Trees-down: bird ancestors were tree-dwellers that jumped between branches. Eventually, they were able to glide and fly greater distances between trees.
Ground-up: early birds ran along the ground as they flapped their wings and jumped into the air.
Wing-assisted incline running (WAIR): early birds ran up an incline while flapping their wings, which made it easier to fly than running along level ground. This hypothesis was tested in an experiment with newly hatched ground birds. Researchers saw that hatchlings used WAIR to develop their flight capabilities as they grew older.
Whether early birds started flying by hopping from tree to tree or running along the ground or up rocks, they achieved something that few of us other vertebrates can brag about. Next time you see a hummingbird flitting from flower to flower, or a pelican scanning the sea for fish, send a nod or wink of appreciation to these avian dinosaurs. They have earned it!
Avian dinosaurs: members of class Aves, also known as birds
Hypothesis: a testable statement about an observation
Powered flight: flight that requires power to attain speed
Transitional fossil: a fossil that has characteristics of both ancestral and more modern forms
Vertebrate: an animal with a backbone
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