DINOSAURS ALL AROUND US
What are the major camps in the dinosaur-bird evolution debate?
There are several camps of paleontologists in the dinosaur-bird evolution debate. One group believes birds descended from certain dinosaurs about 60 million years ago. Another camp believes proto-birds evolved separately from dinosaurs about 200 million years ago. And there is another group that has emerged: scientists who believe that birds are actually dinosaurs. Right now, there are not enough fossils to come to a definite conclusion, and all sides have good arguments. However, with the advent of DNA sequencing, scientists may one day have the answer.
What is cladistic analysis?
Cladistic analysis is a method used to determine an organisms family tree. The older system of classification, developed by Carolus Linnaeus (Carl von Linne, 1707-1778) in the eighteenth century, categorizes plants and animals by organisms overall similar characteristics. Cladistic analysis uses specific characteristics, such as wrist bones, and relates them to previous and following generations, thus tracing the evolution of these structures. The more characteristics previous and following generations share, the more likely they are related. (A cladogram represents a diagram of all the clades, or groups of organisms.)
Cladistic analysis is not easy. Scientists must study the minute details of early animal fossils, noting the tiniest differences in bones and joints. Each different characteristic is assigned a code and added to a computer database. The computer then sorts the information, producing what looks like a family tree, linking together past and modern animals by these detailed characteristics.
What does cladistic analysis tell us about birds and dinosaurs?
According to cladistic analysis, birds share some 132 characteristics with dinosaurs. Some scientists believe this hard evidence indicates that birds are, indeed, a kind of dinosaur. But many scientists still disagree.
How long ago did modern birds originate?
Scientists are still debating this question. Many researchers have suggested, based on fossils and cladistic analysis that modern birds arose around 60 million years ago. But more recent fossil discoveries have caused the debate to become heated, and some researchers suggest modern birds may have evolved more than 100 million years ago. The problem comes with how scientists look at bird evolution: some use the fossil records and others use genetic data, both of which yield conflicting results. New techniques, such as DNA sequencing, may help scientists resolve when and how the worlds close to 10,000 bird species originated.
What recent genome study may rewrite the evolutionary history of birds?
The debate about the origin of birds and their connections to dinosaurs has reached into the molecular lab. For many years, the Early Bird Assembling the Treeof-Life Research Project, centered at The Field Museum in Chicago, has been examining DNA sequences from all major living bird groups. So far, more than 32 kilo- bases of nuclear DNA sequences from 19 different locations on the DNA sequencing have been checked for each of 169 bird species. This massive undertaking has already revealed some birds secrets. For example, distinctive bird lifestyles, such as being nocturnal or raptorial, may have evolved several times. One example is the colorful, daytime hummingbirds that evolved from the darker-colored, nocturnal nightjars. As the studies continue, researchers already know that not only will the names of dozens of birds have to be changed, but so will many biology, paleontology, and birdwatchers field guides.
