By Will Dunham
WASHINGTON (Reuters) - Some of the best-known dinosaurs, like Tyrannosaurus rex and Brontosaurus, may be headed for a divorce due to irreconcilable differences.
Scientists on Wednesday proposed a radical overhaul of the dinosaur family tree first laid out in 1888, concluding after an analysis of 75 species that the meat-eating group that includes T. rex should not be lumped in with the long-necked, long-tailed, four-legged plant-eaters like Brontosaurus.
The proposed new family tree includes two reformulated categories, or clades, of dinosaurs to replace the two that paleontologists have long recognized. The research also pushes dinosaur origins back to relatively soon after a mass extinction that rocked the Earth 252 million years ago.
"We may be proved to be correct, we may not," said University of Cambridge paleontologist Matthew Baron, who led the research published in the journal Nature.
"But what has to happen now is a complete abandonment of old dogmatic views across the field because we have shown that rigorous and objective studies can pull apart age-old ideas, and that we as scientists should never got too comfortable with an idea when it can still be tested in new ways."
Key skeletal differences indicate the meat-eating group called theropods, including giants like T. rex, Allosaurus, Giganotosaurus and Spinosaurus, and the long-necked group called sauropods, including huge Brontosaurus, Diplodocus and Argentinosaurus, should not be banded together, he said.
Scientists long have organized dinosaurs into two clades.
The so-called bird-hipped Ornithischia includes the herbivorous spiky-tailed stegosaurs, tank-like ankylosaurs, horned dinosaurs, duckbills and dome-headed dinosaurs. The so-called reptile-hipped Saurischia covered theropods including birds and the sauropods.
Baron proposed two newly devised categories. The first, called Ornithoscelida, joins the theropods with all the current members of Ornithischia. The current Saurischia group would lose the theropods but add a strange, primitive group of two-legged carnivores called herrerasaurids.
The analysis placed the earliest dinosaur at 242 to 247 million years ago, a small Tanzanian species called Nyasasaurus. After humble beginnings, dinosaurs become the dominant land animals until an asteroid wiped them out 66 million years ago.
"Our results strongly suggest that the ancestral dinosaur was a quick, two-footed, generalist feeder that would have eaten a mix of plants and meat," Baron said.
University of Maryland paleontologist Thomas Holtz, not involved in the study, praised the research, saying, "There is a very good chance that they are correct, even though it goes against decades of research pointing a different way."
(Reporting by Will Dunham; Editing by Sandra Maler)