Branching Out: A Bird's Family Tree

If someone were to ask you what the closest living relative of a bird is, what would be your first guess?

If you’re drawing a blank, you’re not alone. Birds are their own class of animal characterized by the ability to fly, and that always seems to set them apart from the rest. But they must have animal relatives, so who is comparable?

The answer is the crocodile.

Surprised? It does seem an odd comparison. Birds, whom we associate with the elegance and grace of flight, being similar to crocodiles, who are known for raw ferocity and power. But when really examining the two species, the similarities begin to reveal themselves.

Let’s start with feet. A bird’s legs are rough and scaly, much like the skin of their reptilian relatives. Studies have begun unraveling the history of both scales and feathers, and there are several theories of how the two have developed simultaneously. Some scientists believe that reptilian scales were gradually stretched out and frayed, becoming feathers.

Now compare the heads of the animals. The pointed beaks of birds and triangular heads of reptiles are quite similar. The eyes are situated on the sides of the head rather than the front, and they each share the two side skull openings characteristic of their shared family of diapsids.

Not only in appearance are the two similar, but also in biology. More recent studies are revealing that the method of breathing used by birds is also the method used by crocodilians.

Let’s get technical for a moment to illustrate this family tree:

Crocodiles and birds both come from the same branch of diapsida called Archosauriformes. The Archosauriformes are the only group of the diapsida that are not extinct. From there, they reside under the Archosauria label, which includes crocodiles, dinosaurs, pterosaurs, and birds. Finally, the archosauria split off into two categories: Pseudosuchia and Ornithosuchia. The former developed into crocodiles and their relatives, the ladder into dinosaurs, pterosaurs, and birds.


Because the dinosaurs and pterosaurs are long gone, this leaves the bird alone with its cousin, the crocodile.

So the next time you spot a hummingbird zooming through your garden, you can remember the origins of such tiny, delicate creatures and the monstrous crocodiles that are their cousins. (Talk about a family reunion!)

By Brittany Webb, Pandemonium Aviaries Intern

Works Cited

"Alligators Breathe Like Birds, Study Finds." ScienceDaily. ScienceDaily, 15 Jan. 2010. Web. 24 Oct. 2012. <>.

Hutchison, John R., Brian R. Speer, and Matt Wedel. "Archosauria." Archosauria. University of California Museum of Paleontology, n.d. Web. 24 Oct. 2012. <>.

Zimmer, Carl. "Feather Evolution - National Geographic Magazine." Feather Evolution - National Geographic Magazine. National Geographic, Feb. 2011. Web. 24 Oct. 2012. <>.