Dig in Sonora Yields Intriguing Finds

By ERIC SWEDLUND; JAMES GREGG

Fossil fever

Kids help paleontologists find evidence area was a crossroads for varied species

SAN CLEMENTE de TERAPA, Sonora – The curiosity of a 7-year-old boy trumped the expertise of a group of field paleontologists for the find of the day: a tiny owl bone dug from the dirt of the arid badlands of northeastern Sonora.

The site has already revealed a remarkable diversity of prehistoric life, but even a quick examination of Martin Bademi’s discovery impressed the researchers, who say the distinct and well- preserved fossil may be “the key element” in proving the long- extinct owl species was prevalent in the region.

In eight years of excavating, scientists from the University of Arizona and Northern Arizona University – along with colleagues from both sides of the border – have unearthed a wealth of fossils that indicate the area was once a rich biological crossroads for creatures from both tropical and arid regions.

“There are literally tens of thousands of bones, and what we are seeing is a very unique site,” said NAU’s Jim Mead.

“It has crocodile and capybara and all the things you would expect to find with marshes, and yet we’re also finding some of the things you’d find in Arizona – mammoth, bison and horse. It’s that intermixed zone between two environments.”

Mead’s team and various helpers – including, as always, local children – have found about 70 animal types.

The researchers have cataloged everything from crustaceans, snails and fish to crocodiles, capybara, camels and bison. One particularly notable find is fossils from the glyptodont, an extinct, giant armadillo-type creature that Mead described as “a VW bug with an attitude.”

Just as Martin’s sharp eyes brought the key owl bone to researchers, the whole dig is credited to another boy who unearthed a tooth from an extinct elephantlike mammal.

Others from the isolated Opata village overlooking the Rio de Moctezuma started finding more bones in the area and contacted the UA’s Arturo Baez, who grew up nearby.

Baez, now a senior farm supervisor for the campus agricultural center, and Mead, a geology professor and director of NAU’s Laboratory of Quaternary Paleontology, have been leading groups to the site, about 150 miles south of Agua Prieta, Sonora, for week- long digs for the last several years.

“Each time we come back, we’re finding more and more bones, and the neat thing is, we haven’t plateaued,” said Mead, who grew up in Tucson and earned his doctorate from the UA. “Usually when you dig a site, at some point you start finding the same things over and over again. We haven’t reached that.”

Sonora represents a transition zone from the tropical regions of central Mexico to more arid forest regions beginning in Arizona and continuing north. Mead calls it a critical “doorway” from one environment to another that changes as the climate changes.

“For whatever reason, northern Sonora just has not been examined well,” Mead said.

“It’s one of the best-kept secrets because there’s just nobody out here. The paleontologists of Mexico are finding all the stuff they need to keep themselves busy down in central and southern Mexico.”

Further study in the area might turn up more of the diversity of fossils, but for now Terapa remains a unique and inspiring site.

“We’re finding stuff that is just unheard of,” Mead said. “We’re finding this giant armadillo that was thought to occur no farther north than central Mexico, and here we’re getting it 1,000 kilometers farther north and west.”

“In terms of the discipline, we’re learning a lot. In terms of Sonora and that doorway between northern Mexico and the southern U.S., we’re learning tremendous things.”

Mead said that over the years the researchers have been refining a working hypothesis to describe how the fossil-rich deposits were created.

Exposed lava flow in the area oozed out of a volcano vent and was able to spread out and flow down a canyon. The flow pushed the Moctezuma River closer to the mountains, carving out a little basin along the way.

The lava-dammed river produced a short-lived marsh that held diverse and rich wildlife. Most of the animals found since excavation began are either extinct or no longer found in the region.

“This was a semi-tropical environment, probably only along this corridor,” Mead said. “It was a riparian zone that was tropical, and we’re getting some unusual things that haven’t been found this far north.”

The village is the southern edge of the site, and a deep canyon comes in from the south, where it appears the water finally breached the lava.

The deepest portion of the basin is named Camel Bill, where a wall is exposed 11 meters high.

But the site is eroding quickly. “We’d like to find out what all happened here before it all disappears and washes down into the gulf,” Mead said.

For students, the work represents a relaxing and productive spring break, as opposed to the typical big-bash destinations.

Not only is it a chance to dirty their hands as paleontologists, but it’s also a cultural exchange as they engage with the local children curious to help out.

Alicia Al-Aryan, a 23-year-old NAU graduate student studying quaternary science and paleontology, said unearthing fragments of ancient turtle shells reminded her of the time she spent as a child digging in the woods behind her Minnesota house.

“To actually find a little fossilized fish on the side of a rock was pretty exciting, and then you find more and know what to look for,” she said.

“It’s just the experience and getting more familiar with how to actually excavate and find fossils.”

DID YOU KNOW

A dinosaur called Sonorasaurus thompsoni was discovered in the Whetstone Mountains northeast of Sonoita by Rich Thompson in November 1994.

The dinosaur’s bones were well-preserved and embedded in sandstone. Paleontologists from the Arizona-Sonora Desert Museum excavated parts of the skeleton and re-created the setting of the dinosaur’s resting place at the museum. The exhibit opened in 2000.

The Sonorasaurus was a sauropod that lived about 100 million years ago during the Cretaceous period. While digging up the bones, paleontologists also discovered fossils of carnivores that fed on the carcass, including a 2 1/2-inch-long tooth from an Acrocanthosaurus, an 8,000-pound predator from the same period.

Source: Star archives

On StarNet: See more images from the dig at azstarnet.com/ slideshows.

* To contact reporters: Eric Swedlund at 573-4115 or eswedlund@azstarnet.com; James Gregg at 573-4155 or jgregg@azstarnet.com.

Originally published by ERIC SWEDLUND AND JAMES GREGG, ARIZONA DAILY STAR.

(c) 2008 Arizona Daily Star. Provided by ProQuest Information and Learning. All rights Reserved.