Discover 1-2

Theropoda

16

26 DISCOVERMAGAZINE.COM

❯

FOR THE PAST 130 YEARS, paleontologists divided

dinosaurs into two groups, based on a handful

of anatomical features — a split they believe

occurred early in the animals’ evolution more than

230 million years ago. The “lizard-hipped” saurischians

comprised meat-eating theropods such as T. re x and

long-necked, herbivorous sauropodomorphs, such

as Diplodocus. On the other side of the divide, “bird-

hipped” ornithischians included beaked plant-eaters

such as Triceratops.

In March, however, Nature published a proposal that

trashes the traditional family tree. Instead, researchers

placed theropods with ornithischians, forming a group

called Ornithoscelida, and put sauropodomorphs with

the early and primitive herrerasaurs.

“Our new hypothesis has lots of exciting implications

about when and where dinosaurs may have originated,

as well as when feathers may have evolved,” says

University of Cambridge paleontologist Matthew

Baron, lead author of the study.

Not all researchers are so enthusiastic: A number of

early dinosaur evolution experts have challenged the

proposed reorganization. But even some of the critics

are open-minded.

“I don’t think we can be quite sure whether the new

or the traditional arrangement is correct,” says Steve

Brusatte of the University of Edinburgh, “but new

fossils will hopefully help us untangle it.”

Baron and colleagues aren’t waiting for new fossils to

be found, however. In August, they published a reanalysis

of Chilesaurus in Biology Letters. The dinosaur, first

described in 2015 as a bizarre, herbivorous theropod,

is actually a primitive ornithischian, according to the

study — a placement that would strengthen the authors’

argument for rewriting the entire family tree.  JON TENNANT

ESSAY

WHAT IF THE MOST BASIC

THING WE KNOW ABOUT

DINOSAURS IS WRONG?

TOP: GABRIEL LÍO. BOTTOM: JAY SMITH

Chilesaurus

SHAKING THE FAMILY TREE

Traditional dinosaur evolutionary tree

Ornithischia Sauropoda

Dinosauria Herrerasauridae

Saurischia

Proposed revision

Herrerasauridae Sauropoda Theropoda Ornithischia

?

Dinosauria