Miami geologist part of "dawn runner" discovery in early dinosaur graveyard

Miami University geologist Brian Currie is a member of an international team of paleontologists and geologists who report in the Jan. 14 issue of the journal Science the discovery of a previously unknown dinosaur that roamed South America 230 million years ago. Sporting a long neck and tail and weighing only 10 to 15 pounds, the new dinosaur has been named Eodromaeus, the "dawn runner."

Currie and his colleagues describe a near complete skeleton of the new species in their report. The paper presents a new snapshot of the dawn of the dinosaur era during the Triassic time period. Eodromaeus is the oldest known member of an evolutionary lineage that culminated in dinosaurs like Tyrannosaurus rex some 165 million years after their first appearance.

The site of discovery, set in the foothills of the Andes, is known as the “Valley of the Moon,” said the report’s lead author, Ricardo Martinez of Argentina’s National University of San Juan.

“Two generations of field work have generated the single best view we have of the birth of the dinosaurs,” Martinez said. “With a hike across the valley, you literally walk over the graveyard of the earliest dinosaurs to a time when they ultimately dominate.”

Currie's work on the project focused in refining the geological stratigraphy (rock layers) and structure of the study area and interpreting the depositional environments of the basin in which the earliest dinosaurs lived. The area was once a rift valley in the southwest corner of the supercontinent Pangaea. Over the course of approximately five million years, ancient rivers deposited sediments that accumulated a thickness of more than 2,000 feet (700 meters). Volcanoes occasionally spewed volcanic ash into the valley, allowing the team to use radioactive elements in the ash layers to determine the age of the deposits.

In the oldest deposits, Eodromaeus lived alongside Eoraptor, a similar-sized plant-eating dinosaur that team members discovered in the valley in 1991. Eoraptor’s descendants would eventually include the giant, long-necked sauropods. Eodromaeus, with stabbing canine teeth and sharp-clawed grasping hands, is the pint-sized precursor to later meat-eaters called theropods, and eventually birds, say the researchers.

The authors logged thousands of fossils unearthed in the valley. The fossil data presented in the Science article provide an early glimpse into the evolutionary origins of dinosaurs.

"Analysis of the fossils from Argentina reveal that the different dinosaur lineages were all represented during their early history, but at the time they contained many similarities," Currie said.

In the youngest rocks of the valley, larger plant- and meat-eating dinosaurs had evolved many times the size of Eoraptor and Eodromaeus, but it would be even later when they dominated all land habitats in the succeeding Jurassic and Cretaceous periods.

“The story from this valley suggests that there was no single advantage or lucky break for dinosaurs but rather a long period of evolutionary experimentation in the shadow of other groups,” said co-author Paul Sereno, University of Chicago paleontologist.

Along with Martinez, Serano and Currie, the other study authors are Oscar Alcobar and Carina Colombi of the National University of San Juan; Paul Renne of University of California, Berkeley; and Isabel Montanez, University of California, Davis. Colombi was a visiting international research scientist at Miami in 2004-2005.

Currie, associate professor of geology at Miami, was also part of a team that uncovered evidence of the oldest hominid skeleton yet reported, Ardipithecus ramidus, known as Ardi. The Ardi report, which was co-authored by Bill Hart, chair and professor of geology, among others, appeared in a special issue of Science (Oct. 2, 2009) and was named the magazine’s “Breakthrough of the Year” for 2009.

This article contains text from the University of Chicago press release.