How did birds evolve from theropod dinosaurs?

Birds evolved during the Jurassic period from a specialized group of theropod dinosaurs known as Paraves. Current scientific consensus places birds firmly within the dinosaur clade, sharing numerous skeletal and physiological traits with their extinct relatives. Four distinct avian lineages survived the Cretaceous-Paleogene extinction event, eventually diversifying into the thousands of species living today.

What we know

• The evolution of birds began in the Jurassic period with their derivation from a clade of theropod dinosaurs named Paraves. [2]
• For over a century, the small theropod Archaeopteryx lithographica from the Late Jurassic period was considered the earliest bird. [2]
• Fossils of more than thirty species of non-avian dinosaurs have been found with preserved feathers, including small forms with long arm and leg feathers. [4]
• Four distinct lineages of birds survived the Cretaceous-Paleogene extinction event 66 million years ago to give rise to modern groups. [2]

Still open

• The exact relationship between non-avian dinosaurs, Archaeopteryx, and modern birds remains under debate.
• A small minority of scientists dispute dinosaurian ancestry, arguing instead that birds share a common stem-ancestor with theropods among more basal archosaurian lineages.

Where to go next

• what caused itWhat caused the extinction of non-avian dinosaurs?
• how it workedHow did powered flight develop in early birds?
• how we knowWhat shared skeletal features link birds and dinosaurs?
• the bigger pictureHow are living birds classified into modern groups?
• a case in pointWhat was the role of Archaeopteryx in evolutionary history?
• an unexpected connectionWhy are crocodiles the closest living relatives of birds?Despite birds being living theropod dinosaurs, their closest surviving biological relatives outside of dinosaurs are crocodilians, with both forming the archosaur clade.

Sources

• [1]evolution of birds (Wikidata Q468822) · CC0 1.0
• [2]Evolution of birds · CC BY-SA 4.0
• [3]Bird · CC BY-SA 4.0
• [4]Origin of birds · CC BY-SA 4.0
• [5]Alan Feduccia · CC BY-SA 4.0