Illustration by Ian Berry.

'Giant flying murder heads' and other creatures that ruled the ancient sky

Updated 9:19 AM ET, Mon September 27, 2021

Science has transformed our understanding of dinosaurs in the past two decades. Get caught up with what's new in this five-part CNN series.

(CNN)One close glimpse of a modern bird, especially around the eyes, and it may feel like you're looking into the ancient past, when massive creatures walked the Earth and soared across its skies. It's because birds are dinosaurs -- they just happened to survive the mass extinction event that wiped out their large relatives 66 million years ago.

Today, birds are one of the most diverse groups of vertebrates, and they've had a long time to evolve. The first "bird" in the fossil record is largely considered to be Archaeopteryx, which existed 155 million years ago. Around 55 million years ago, the first hummingbirds and parrots began to appear.