You may have heard that modern birds evolved from dinosaurs before. More specifically, modern birds descend from theropods, which is a clade of dinosaurs. A clade is a group of species that share some key traits as well as common ancestry. Theropods all had hollow bones and three toed limbs, traits that remain in modern birds. The most famous of theropods was the T. Rex, but you also may have heard of the Spinosaurus, Archaeopteryx, and Allosaurus.
How did we come to this conclusion? It turns out hollow bones and three toed limbs are not the only similarities between theropods and modern birds. Various types of theropods have also been found to have feathers in fossilized remains. Older theropod species, that are “farther” back from dinosaurs on the tree of life, only had one kind of feather, which paleontologists think was used for insulation. Younger theropods, more closely related to birds, such as the oviraptors, had multiple different kinds of feathers. While some of these feathers are also for insulation, others are very similar to the flight feathers on modern birds. Modern birds have three “fingers” in the bone structure that supports their wings. Groups of dinosaurs that are theorized to be closely related to modern birds tend to have less and less fingers. The Orinsthican dinosaurs, very distant ancestors to birds, had five fingers. The Allosaurids, closer ancestors, had four fingers. Eventually, dinosaurs like Archaeopteryx had three fingers, which would eventually lead to the development of modern birds’ wings. Over time, the tails of dinosaurs began to get shorter and shorter. Eventually, the tails got so short that they’re barely there, until the only modern evidence of them are the tail feathers on the backs of birds.
Agnolin, F. L., Motta, M. J., Brissón Egli, F., Lo Coco, G., & Novas, F. E. (2019). Paravian phylogeny and the dinosaur-bird transition: An overview. Frontiers in Earth Science, 6(February), 1–28. https://doi.org/10.3389/feart.2018.00252
The origin of birds – Understanding Evolution. (n.d.). Retrieved December 2, 2021, from https://evolution.berkeley.edu/what-are-evograms/the-origin-of-birds/
Theropod | dinosaur suborder | Britannica. (n.d.). Retrieved November 30, 2021, from https://www.britannica.com/animal/theropod