The family tree used by paleontologists for nearly 130 years to classify species of dinosaurs may soon face extinction.

Scientists at the University of Cambridge and the Natural History Museum in London this week proposed a wild new hypothesis that is likely to force a rewrite on how various dinosaur lineages are related.

Writing in the journal Nature, the team suggests that the current method of arranging dinosaurs based on the structure of their pelvic bones is incorrect. Currently, the family tree is divided into either Ornithiscian (bird-hipped dinosaurs) or Saurischia (reptile-hipped dinosaurs), with more specific branches, like theropods (T. Rex) and sauropods (Brontosaurus), sprouting off from each.

The current method for classifying dinosaurs based on pelvic bones was created by Harry Seeley in 1887. The current method for classifying dinosaurs based on pelvic bones was created by Harry Seeley in 1887. (Photo: Nature)

The problem, according to study lead author Matthew Baron of the University of Cambridge, is that while dividing dinosaurs based on hip bones may have worked well in the late 19th century, modern paleontologists have more data, technology, and most importantly, many more fossils with which to better understand dinosaur evolution.

Working on a hunch that the current system was flawed, Baron led a team that meticulously studied and compared 457 anatomical features of 74 different dinosaurs. After three years, they came up with a new tree that, among other changes, places Theropoda and Ornithischia under a new unified group called “Ornithoscelida.”

“When we started our analysis, we puzzled as to why some ancient ornithischians appeared anatomically similar to theropods," he told Forbes. "Our fresh study suggested that these two groups were indeed part of the same clade. This conclusion came as quite a shock since it ran counter to everything we'd learned.”

Under the new classification system, theropods like T. Rex are now grouped with bird-hipped dinosaurs such as Stegosaurus under 'Ornithoscelida.' Under the new classification system, theropods like T. Rex are now grouped with bird-hipped dinosaurs such as Stegosaurus under 'Ornithoscelida.' (Photo: Nature)

Besides shaking up the family tree, Baron and his team also propose changes to both the arrival of dinosaurs on Earth's timeline and their potential origin.

Previously, scientists believed dinosaurs emerged some 237 million years ago on an ancient supercontinent called Gondwana. In the paper, the researchers say the first dinosaurs actually showed up slightly earlier –– about 247 million years ago, somewhere in the northern region of the supercontinent Laurasia.

Whether or not the proposed family tree becomes accepted by the wider paleontological community, it's clear that the research has already made some reconsider how dinosaur species are related.

“This is a textbook changer — if it continues to pan out,” Thomas Holtz, a vertebrate palaeontologist at the University of Maryland in College Park, told Nature. “It’s only one analysis, but it’s a thorough one.”

Michael d'Estries ( @michaeldestries ) covers science, technology, art, and the beautiful, unusual corners of our incredible world.