"Archaeopteryx is considered by many to be the first bird, being about 150 million years old. It was the first reptilian fossil found with clear evidence of feathers, a trait long considered the key distinction between birds and “non-birds.”
“Scientists have argued, ‘feathers are unique. They can only evolve in birds. If you have feathers you are a bird,’ ” says Clark. “Now you have dinosaurs with feathers.”
Scientists quickly recognized this member of the therapod family as the potential “missing link” between birds and more primitive reptiles. Like many dinosaurs, archaeopteryx had a bony tail, teeth, and clawed fingers, and a hyperextendable claw on each foot. However, this species also had several features similar to birds such as its feathers, wings, wishbone, and reduced tail vertebrae. Many scientists believe these feathers may have originally evolved for insulation and later were co-opted for flight."
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