The researchers, reporting in the July 22 issue of the journal Science, also found that chromosomal evolution has accelerated, based on the rate of breakages and reorganization, since the extinction of dinosaurs 65 million years ago.
In a study led by Harris A. Lewin of the University of Illinois at Urbana-Champaign and William J. Murphy of Texas A&M University, the organization of chromosomes of humans, mice, rats, cows, pigs, dogs, cats and horses was compared at high resolution.
"This study has revealed many hidden secrets on the nature and timing of genome evolution in mammals, and it demonstrates how the study of basic evolutionary processes can lead to new insights into the origin of human diseases," said Lewin, the director of the Institute for Genomic Biology at Illinois and a professor of animal sciences.
The multi-species comparison was aided by a computer visualization tool -- the "Evolution Highway" -- developed by collaborators in the Automated Learning Group at the National Center for Supercomputing Applications at Illinois. Other lead participants were from the University of California at San Diego and the Genome Institute of Singapore.
The acceleration of evolution since dinosaurs disappeared surprised the researchers, who studied a computer-generated reconstruction of genomes of long extinct mammals, including the ancestor of the majority of living placental mammals of 94 million years ago.
"Based on our findings of the mammalian rate speed-up, we postulate that early mammals, with conservative body plans, retained fairly conserved genomes, as evidenced in the striking similarities in the reconstructed ancestral genomes," Murphy said.