The most salient trait of birds is their ability to fly. Flight allows peregrine falcons to dive at just over 200 miles/hour, flight allows for migration, and flight allows birds like albatrosses to make vast expanses of ocean their home. Indeed, the evolution of flight was a critical event (and maybe the critical event) in the evolution of birds. Given the importance of flight for the class Aves, evolutionary biologists have long studied the origins of flight, and researchers are beginning to delineate how and why birds evolved flight.
|Peregrine Falcon, Point Reyes, CA. Dec. 2011 [Photo by Lukas Musher]|
Birds’ closest ancestors were theropod dinosaurs (1). We all know what theropods dinosaurs are thanks to Jurassic Park (and as far as I’m concerned, only one Jurassic Park movie was ever made and it came out in 1993). As depicted in Jurassic park dinosaurs such as Velociraptor (see below), which is actually much smaller than depicted in the movie , and Tyrannosaurus, which may have been more of a scavenger than a predator, are both examples of theropod dinosaurs. In general, theropods were bipedal dinosaurs with strong hindlimbs and a long tail that was likely used for balance. From theropods we get birds, here is a woefully brief description of how.
|An artist's rendition of velociraptor [Wikipedia]|
|An artist's rendition of anchiornis [National Geographic]|
|Proto-feather evolution in chronological order. [Wikipedia]|
|Wings, such as the long wings allowing Black-footed Albatross to wander countless miles over vast expanses of ocean|
evolved from the forelimbs of therapod dinosaurs. Pelagic out of Fort Bragg, CA. Aug. 2011. [Photo by Lukas Musher]
What I will mention as an aside is the downstream evolutionary consequences after wings evolved. After proto-birds lost any sort of forelimb dexterity, the duty of manipulating objects was transferred to the beak. This transfer likely explains the extraordinary diversity of bill forms, compared to other groups. So lets assume that the wing morphology is coming into place, even with wings, other physiological structures and adaptations were necessary to yield contemporary birds. Among the adaptations are hollow bone structures that largely reduce the weight of a bird (1), and save the bird significant amounts of energy during flight. And to actually get into flight, birds rely on their oversized breast muscles, which became so powerful that they need to be anchored to a keeled sternum.
|Archeopteryx lithographica, Wyoming Dinosaur Center. Taxonomically the first bird. One of 8 specimens worldwide. |
Note the details of feathers and other traits that link dinosaurs to birds including the furcula. [Photo by Lukas Musher]
Gavin Leighton is a PhD candidate at the University of Miami, studying cooperative behavior in Socialble Weavers. See more on Gavin at Guest Writers.
1 Kaiser, G. The inner bird: anatomy and evolution. 386 (2007).
2 Prum, R. & Brush, A. Which came first, the feather or the bird? Sci Am 288, 84-93 (2003).
3 Vinther, J., Briggs, D. E. G., Clarke, J., Mayr, G. & Prum, R. O. Structural coloration in a fossil feather. Biol Letters 6, 128-131, doi:10.1098/rsbl.2009.0524 (2010).
To read the Why of Fly - the Origin and Evolution of Flight in Birds: Part 2, click here.