Some of the most basic categories in the dinosaur family tree may be in need of a rewrite.
For around 130 years, scientists have divided dinosaurs into two major groups (called "clades"), based in large part on their bone structure, especially the shape of their hips. These two groups are the Ornithischia (or "bird-hipped") and the Saurischia (or "lizard-hipped") dinosaurs.
But now, a group of researchers says this scheme is wrong.
Famous lizard-hipped Saurischians include Tyrannosaurus rex, (and many of the other bipedal carnivore dinosaurs, called theropods), whereas Ornithischians included dinosaurs such as Stegosaurus.
The study, which was published Wednesday in the journal Nature, now calls for theropods such as T. rex to be grouped with the Ornithischians, and for sauropods (including Brontosaurus, Apatosaurus, and Brachiosaurus) to be included with a group of early dinosaurs called Herrerasauridae.
The paper also suggests also suggests dinosaurs may have originated in the Northern Hemisphere, rather than in the Southern supercontinent of Gondwana.
"The repercussions of this research are both surprising and profound," said study co-author David Norman, of the University of Cambridge. "The bird-hipped dinosaurs, so often considered paradoxically named because they appeared to have nothing to do with bird origins, are now firmly attached to the ancestry of living birds."
Members of the paleontology community have differing opinions on the certainty of the study's findings.
While apparently impressed with the research, some paleontologists are cautioning against overstating the certainty of paper's conclusions. Kevin Padian, a vertebrate paleontologist at the University of California, Berkeley, told Nature News that the study will, at the very least, "send people back to the drawing board."
Smithsonian Institute paleontologist Hans-Dieter Sues told Nature News, "I caution against totally reorganizing the dinosaur family tree just yet," because analyses of relations among species is dependent on the factors being considered.