Not many people realize that taxonomically modern birds are actually a form of reptile: evidence that birds are descended from dinosaurs. But the evolutionary history of birds and where they officially separated themselves from dinosaurs has historically been a confusing topic for paleontologists. Their capability of flight and the traits that come with this ability is murky and has long perplexed scientists.
The power of flight required several evolutionary adaptations. Besides physiological changes in the muscular and skeletal systems to support the physical aspects of flight, a bigger more powerful brain is also thought to be a key characteristic necessary to fly. A larger skull to hold a larger brain has been tracked as a defining feature of avian dinosaurs.
For a long time, Archaeopteryx was pointed to as the first bird because it has been shown to have the power of flight and shows many intermediary characteristics of both avian and non-avian dinosaurs. Archaeopteryx lived in the Jurassic around 150 million years ago. However, due to a recent study in Nature published by Amy Balanoff et al., Archaeopteryx may now be unseated as the first bird. The study used CT scan data to compare the skull size of Archaeopteryx to 10 non-avian dinosaurs and 20 modern birds.
The results showed that Archaeopteryx actually had a smaller skull than some of its non-avian dinosaur relatives and was not in the middle of the data as expected. This means that the complex brain of Archaeopteryx may have been present in non-avian relatives. Although this shifts the timeline making the high powered brain appear before the power of flight, this result does not necessarily upset Archaeopteryx from its title of first bird. As Dr. Balanoff says "Archaeopteryx is in the evolutionary middle-- but it's not uniquely in the middle."
Source:
Balanaoff, A., Bever, G., Rowe, T., & Norell, M. (2013). Evolutionary origins of the avian brain. Nature, 501, 93-96. doi:10.1038/nature12424
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