What Was the First Bird? Tracing Avian Ancestry

Birds are one of the most fascinating creatures on earth, not only for their current diversity but for their evolutionary history. The first birds appeared on the earth millions of years ago, and since then, birds have occupied almost every habitat on the planet. One of the most significant questions in the field of ornithology is: What was the first bird? The answer to this question has long perplexed paleontologists and evolutionary biologists. In this article, we will trace the ancestry of birds to try and uncover the answer to this intriguing question.

The Origin of Birds

Birds belong to the class Aves that includes more than 10,000 species, making it one of the most diverse classes of terrestrial vertebrates. The oldest known bird species is Archaeopteryx lithographica, which lived during the Late Jurassic period 151 to 143 million years ago. Archaeopteryx had a mix of bird and reptilian features, such as wings and feathers, but also had a long bony tail, clawed fingers, and teeth. This dinosaur-bird hybrid is considered a transitional fossil between non-avian theropod dinosaurs and modern birds.

The Relationship Between Birds and Dinosaurs

The discovery of Archaeopteryx has led to the realization that birds descended from dinosaurs. Theropod dinosaurs, such as the Velociraptor and T. rex, share many skeletal features with birds, such as the wishbone and hollow bones. These similarities suggest that birds emerged from a group of small, feathered theropod dinosaurs known as paravians about 160 million years ago in the late Jurassic period.

The paravians were a diverse group of dinosaurs that included the well-known Velociraptor and the less familiar Anchiornis. Anchiornis, which lived about 160 million years ago, had feathers covering its legs, arms, and tail, and also had body feathers. These characteristics suggest that Anchiornis, and potentially other paravians, may have flown, albeit in a rudimentary fashion, and were likely to have been among the first true birds.

Other Potential Ancestors of Birds

While modern birds are descendants of small theropod dinosaurs, other groups of archosaurs (the group of animals that includes crocodiles, dinosaurs, and birds) may have given rise to birds as well. Some scientists believe that basal archosaurs, such as the long-gone Proterosuchidae, may have been one of the first archosaurs that evolved into birds. However, definitive fossils to support this theory are lacking as of now.

What Separates Birds from Dinosaurs?

While dinosaurs and birds share many characteristics, such as feathers, there are some important differences that allow us to distinguish birds from their dinosaur ancestors. These differences include:

  • Birds have a beak instead of teeth. The earliest known birds, such as Archaeopteryx, had teeth, but the earliest modern birds had lost their teeth.
  • Birds’ skeletons are lighter and more streamlined than those of their dinosaur ancestors, which facilitated the development of flight.
  • Birds have unique respiratory systems, with separate air sacs that allow them to breathe more efficiently than other animals of similar size.
  • Birds have a more efficient circulatory system that can support high metabolic rates required for flight.
  • Their digestive system is adapted to their diet, which primarily consists of grains and other plant matter, while dinosaurs had a more carnivorous diet.

The Evolution of Modern Birds

After Archaeopteryx, birds evolved into many different forms. They survived a mass extinction that wiped out non-avian dinosaurs and other animals about 66 million years ago. Since then, birds have diversified and occupy almost every habitat on the planet, from the Arctic to the Antarctic, from deserts to forests, and even the open ocean. However, it is still unclear exactly how bird evolution proceeded after Archaeopteryx.

One notable group of birds that emerged after Archaeopteryx were the enantiornithines, a group of birds with teeth that lived during the Cretaceous period about 100 million years ago. The enantiornithines are a sister group to modern birds but became extinct at the end of the Cretaceous period (along with non-avian dinosaurs). Scientists believe that enantiornithines were once as diverse as modern birds and filled many of the ecological niches that modern birds occupy today.

The Avian Explosion

While enantiornithines were a significant group of early birds, modern birds (the group known as Neornithes) did not emerge until after the Cretaceous-Paleogene extinction event. After this mass extinction, modern birds diversified rapidly and explosively, leading to the development of many of the modern bird families we see today. Within a few million years, the ancestors of all the modern bird groups – from songbirds to eagles – had emerged. This period of rapid diversification is known as the “avian explosion.”


The first bird is widely believed to have been a paravian dinosaur that lived in the late Jurassic period about 160 million years ago. However, since birds and dinosaurs share many characteristics, it’s difficult for scientists to pinpoint an exact species or group of species that was the first bird. To date, the oldest known bird is Archaeopteryx, a dinosaur-bird hybrid that lived about 150 million years ago. The evolution of modern birds is a fascinating journey that spans tens of millions of years, and much is still unknown about this process.

Common Questions Related to Bird Evolution

  • Q: What distinguishes birds from dinosaurs?
  • A: There are several differences between birds and dinosaurs, including their respiratory and circulatory systems, their skeletal structure, and their diet.
  • Q: When did the first modern birds emerge?
  • A: Modern birds emerged after the Cretaceous-Paleogene extinction event that wiped out non-avian dinosaurs and many other animals.
  • Q: What is the oldest known bird?
  • A: The oldest known bird is Archaeopteryx lithographica, which lived during the Late Jurassic period about 150 million years ago.
  • Q: Are birds the only surviving dinosaurs?
  • A: Yes, birds are the only surviving members of the dinosaur group and are closely related to theropod dinosaurs such as Velociraptor.


  • Brusatte, S. L., O’Connor, J. K., & Jarvis, E. D. (2015). The origin and diversification of birds. Current Biology, 25(19), R888-R898.
  • Feduccia, A. (2012). Riddle of the feathered dinosaurs. Yale University Press.
  • Saunders, J. J., & Dzierzon, M. (2017). “Birds” in Dinosaurs: The Grand Tour. Pegasus Books.
  • Zhou, Z., & Zhang, F. (2002). A long-tailed, seed-eating bird from the Early Cretaceous of China. Nature, 418(6896), 405-409.

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