New Find At Ghost Ranch, New Mexico Shows Dinosaurs Coexisted With Their Predecessors For 15 To 20 Million Years

by AMNH on


A new species of dinosauromorph (lower left) was among the mixed assemblage of dinosaurs and dinosauromorphs found at Hayden Quarry in Ghost Ranch, N.M.

CREDIT: Donna Braginetz

For decades, paleontologists thought dinosaurs existed with their immediate ancestors for only a relatively short period of time before dinosaurs flourished and dominated the planet. However, a recent discovery by paleontologists from the American Museum of Natural History; the University of California, Berkeley; and other institutions overturns this view with the first evidence showing dinosaurs originated earlier and the two groups of animals coexisted much longer than previously believed. Their findings appear in the July 20 issue of the journal Science.

The paleontologists were digging for fossils last year at Hayden Quarry, a new excavation site on the fossil-rich grounds of Ghost Ranch, New Mexico, when they discovered a surprisingly diverse collection of bones that included the first evidence of dinosaurs and less-advanced dinosauromorphs from the same time period. The discovery indicates that the two groups lived together during the early Triassic period 235 million years ago. 

The find also overturns the widely held view that dinosaurs diversified and replaced their predecessors as the planet's dominant land animal relatively quickly in the late Triassic period 200 to 230 million years ago. The new finding suggests that dinosaurs and dinosauromorphs coexisted for at least 15 to 20 million years before an unknown event or series of events led to the rise of dinosaurs.

"The co-occurrence of these animals demonstrates that the rise of dinosaurs was gradual, not sudden," said Sterling Nesbitt, a graduate student in the Museum's Division of Paleontology and who, along with Randall Irmis from the University of California, Berkeley, was co-lead author on the paper. "Whether they were able to replace dinosauromorphs by out-competing them or for some other reason, and how long the transition actually took, remain to be seen."

At the time these animals roamed the Earth, all of the continents were connected in a single landmass known as Pangaea, and Hayden Quarry was located near the equator. The assemblage of bones unearthed at the site further supports mounting evidence that dinosaur diversity varied across Pangaea, with far northern and southern species differing markedly from those found in mid-latitude regions such as Hayden Quarry.

The team also discovered a new species of dinosauromorph and named it Dromomeron romeriafter Alfred Sherwood Romer, the paleontologist who first described early dinosauromorphs in the early 1970s.

The work was supported by the National Geographic Society, Dave Clark Inc., the Theodore Roosevelt Memorial Foundation, the Jurassic Foundation, a Bryan Patterson Memorial Grant, the National Science Foundation, and the University of California, Berkeley.

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