How Birds and Reptiles are Related
Here at the zoo, we specialize in reptiles and amphibians, and that includes exhibits with emus and parakeets. Because of this, we often hear feedback from visitors wondering why on earth we have birds at a reptile zoo. Well, the short answer is…birds are reptiles! However, that wasn’t always the case. Let us explain.
There are four major groups of reptiles living today: turtles/tortoises, lizards/snakes, crocodilians, and dinosaurs. The last two groups are archosaurs, a very specialized group of reptiles that have been around for 225 million years! Archosaurs are the living reptiles that birds are most closely related to.
Here’s a more detailed explanation from Arizona State University’s Ask a Biologist:
Birds are most closely related to crocodiles. To understand this, we should look at some history. The first groups of reptiles evolved about 300 million years ago. About 40 million years later, (very quickly by geologic standards), a group of reptiles called therapsids branched off, which eventually became modern mammals. Other groups of reptiles split off over the next 120 million years, and one branch called the dinosaurs were very successful. These dinosaurs were only distantly related to modern snakes, lizards, and turtles, groups that had split off at different times. But 65 million years ago there was a massive extinction event, and all dinosaurs were killed except for a single group of feathered dinosaurs. These evolved over the next 65 million years into modern birds. So birds aren’t just closely related to dinosaurs, they really are dinosaurs!
© Arizona Board of Regents / ASU Ask A Biologist.
The Missing Link
For centuries, many scientists hypothesized that birds were reptiles due to similarities in their anatomy, but there was no hard fossil evidence to support it. But in 1860, archaeologists discovered a fossil of a highly detailed Archaropteryx lithographica (a bird-like dinosaur), which filled the void of the “transitional species” that scientists needed to link birds and reptiles. Since then, many fossils of feathered dinosaurs have been found.
Dinosaurs and Birds
Although the living reptiles birds are most closely related to are crocodilians (archosaurs), when it comes to their relation to dinosaurs, birds evolved from theropod dinosaurs. These theropods share over 100 traits with modern birds. Here are a few:
- Three forward-facing toes
- Fused collarbone, called a wishbone (yes, that kind of wishbone!)
- Hollow bones
Of course, not all theropod dinosaurs could fly—can you imagine a flying Tyrannosaurus rex?! Some dinosaurs didn’t have the right skeletal adaptations or their feathers were rudimentary. It is thought that feathers were originally used for mating displays, and modern birds still use them for that today.
As mentioned above, a mass extinction event 65 million years ago caused rapid global events like tsunamis and volcanic eruptions. When resources became scarce, larger animals were at a disadvantage, and all non-avian dinosaurs died. Ultimately, the need to adapt to a changing environment drove the evolution of birds and made them successful. Modern birds evolved directly from dinosaurs, and today, there are between 9,000 and 10,000 species of birds!