May 28, 2014
Less Diversity Found In Bird Species Of 125M Years Ago
Brett Smith for redOrbit.com - Your Universe Online
While the typical American wetland hosts a range of birds with different physiologies and behaviors, bird diversity in prehistoric times was significantly lower, according to a new study published in the journal Proceedings of the Royal Society B.
"There were no swans, no swallows, no herons, nothing like that. They were pretty much all between a sparrow and a crow," said study author Jonathan Mitchell, an evolutionary biologist at the University of Chicago.
The researchers began their study by looking at a group of bird fossils dating back about 125 million years ago, when birds first emerged during the Cretaceous. Fossils in the study were compiled from a region in China where there was once heavy volcanic activity, which led to a variety of well-preserved samples. The scientists looked at the range of species in this group, but because fossils show only the physical qualities of the birds, the researchers needed to conduct further analyses to learn the range of bird behaviors.
Next, the researchers looked at 1,400 modern-day birds to construct a statistical method which could connect the physical qualities of a bird to its diet, behavior and habitat. For example, lengthy legs could possibly be connected with birds that wade through water, and the form of the beak might be a clue as at what the bird ate for food.
The study team noted that models based on modern birds may not necessarily apply to birds of the Cretaceous.
"These birds are very different from modern birds—some of them have teeth, some of them have long bony tails," Mitchell said.
To support their model, the team then examined any preserved contents of the birds' stomachs to get a glimpse of their diet. They discovered a connection between the method's estimations and the birds' diet, suggesting that the model would work for ancient birds.
Finally, the model was applied to the Chinese fossil collection. The researchers discovered that birds of the Cretaceous were less diverse than modern birds. Larger birds and water birds were found to be largely absent.
"They were all pretty much the same. They were ground-dwelling or forest-dwelling little birds, mostly eating insects and seeds," Mitchell said.
To determine if their collection of fossils may have been skewed by the fossilization process, the researchers also applied their model to more recent fossils and came to the same conclusions. In fact, the researchers found that the more recent fossils were biased towards larger birds – the opposite bias of the Cretaceous fossils and confirmation that the earlier fossils were not biased via the fossilization process.
The study team theorized that the lack of diversity among Cretaceous birds was due to their newness on the scene and inadequate time to diversify.
"It looks like they just hadn't evolved the crazy diversity of ecologies that we see in modern birds," Mitchell said.
The study team said their results have implications for theories surrounding how and when birds originated.
"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," said study author Peter Makovicky, from The Field Museum of Natural History in Chicago.
Image 2 (below): 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 on a new study about bird evolution during the Cretaceous. Credit: Allison Elaine Johnson