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Contact: Steve Koppes
University of Chicago

Prehistoric birds lacked in diversity

IMAGE: Jeholornis, an early bird, lived during the early Cretaceous period approximately 120 million years ago. The evolution of Jeholornis and other Cretaceous birds is the subject of a new paper...

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To tease out the ecological roles played by the prehistoric birds, the researchers used modern-day birds to build a statistical technique that could relate the physical characteristics of a bird to its diet, behavior and habitat. Long legs might be associated with birds that wade through water, for instance, and the shape of the beak might hint at what the bird ate. For this purpose, the scientists painstakingly measured 1,400 modern birds--mostly from the Field Museum's collections--and extracted the correlations between these measurements and the birds' behavior.

IMAGE: Longipteryx, an early bird, lived during the early Cretaceous period approximately 120 million years ago. Research at the University of Chicago and the Field Museum shows that the birds during...

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Toothy birds

However, the scientists still had to show that this technique, which was useful for modern birds, could be applied effectively to the distinct sample of ancient birds. "These birds are very different from modern birds--some of them have teeth, some of them have long bony tails," said Mitchell. Therefore, it wasn't clear if the method would translate.

In order to test the method, they looked at the contents of the birds' stomachs--the last meals they ate before their demise--which in some cases had survived the process of fossilization. They found agreement between the method's predictions and the birds's diet, indicating that it worked for ancient birds as well.

Once they had confirmed that the method was effective for the fossil birds with food preserved in their bellies, the scientists applied their method to the full complement of the region's bird fossils. They found that these early birds were less diverse than modern birds. In particular, larger birds and water birds were lacking. "They were all pretty much the same. They were ground-dwelling or forest-dwelling little birds, mostly eating insects and seeds," said Mitchell.

Fossilization bias?


IMAGE: Confuciusornis, an early bird, lived during the early Cretaceous period approximately 120 million years ago. University of Chicago graduate student Jonathan Mitchell has collaborated with Field Museum paleontologist Peter Makovicky...

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The scientists' research is beginning to untangle some possible reasons for this lack of diversity. One feasible explanation is that early birds were less diverse due to competition with similar groups--such as the prehistoric flying reptiles known as pterosaurs. But the scientists used an evolutionary model to show that the paucity of ecological niches could be explained simply by the fact that birds were new to the scene, and thus hadn't had time to diversify. "It looks like they just hadn't evolved the crazy diversity of ecologies that we see in modern birds," said Mitchell.


The results have implications for when and how birds originated--a topic under some debate--as well as for the study of evolution in general. "In a broader sense, I think that our research speaks to an understanding of how groups of organisms, which are perhaps dominant today in modern ecosystems, get to that point," Makovicky, said. Birds, for example, evolved from humble beginnings into the diverse group we know today. The early bird, therefore, may indeed have gotten the worm--or the insect or seed--but not much else.


Citation: "Low ecological disparity in early Cretaceous birds," by Jonathan H. Mitchell and Peter J. Makovicky, May 28, Proceedings of the Royal Society B.

Funding: National Science Foundation.


