Approximately 85 million years ago, a family of bird-like dinosaurs with large claws and short, powerful forearms named Alvarezsauroidea roamed the earth. But after a decade of research, a discovery by GW researchers has revealed previously unknown stages in the dinosaurs’ evolutionary development — and extended their fossil record back another 63 million years.
A 10-foot-long, nearly complete skeleton from the family Alvarezsauroidea was found preserved in river-lain rock in the Xinjiang Autonomous Region of northwestern China, a region well-known for fossils from the beginning of the Late Jurassic period, approximately 162 to 158 million years ago. George Washington University doctoral candidate Jonah Choiniere named the specimen Haplocheirus sollers, or “simple, skillful hand.”
“Haplocheirus is a transitional fossil, because it shows an early evolutionary step in how the bizarre hands of later alvarezsaurs evolved from earlier predatory dinosaurs,” says Mr. Choiniere. “The fossil also confirms our prediction that Alvarezsauroidea was evolving during the Late Jurassic time period.”
The fossil contains several distinguishing features that link it to Alvarezsauroidea, a family of dinosaurs that was previously thought to be a flightless offshoot of ancient birds. Despite skeletal similarities between the dinosaurs and ancient birds, Mr. Choiniere’s research demonstrates that the family Alvarezsauroidea evolved in parallel to birds and did not descend from them. The new species shows some of the earliest evolutionary stages in the development of a short, powerful arm with a single functional claw that may have been used for digging termites.
Mr. Choiniere collaborated on a report about the discovery in the Jan. 29 edition of Science with James Clark, the Ronald B. Weintraub Professor of Biology in GW’s Columbian College of Arts and Sciences, and Xu Xing of the Chinese Academy of Sciences’ Institute of Vertebrate Paleontology and Paleoanthropology. Drs. Clark and Xing, along with Associate Professor of Biology Cathy Forster, collected this new species of dinosaur in 2004 during a series of expeditions to Xinjiang. Until now, there was no direct evidence that dinosaurs of this type lived during the late Jurassic period.
“The primary goal of our expeditions was to find evidence of the theropod dinosaurs closest to birds, and the discovery of Haplocheirus is one of our major discoveries,” says Dr. Clark.
Funded by the National Science Foundation Division of Earth Sciences, the National Geographic Society, the Chinese National Science Foundation and GW, the expeditions have unearthed several other interesting discoveries, including a small, agile relative of crocodilians (Junggarsuchus sloani), the oldest horned dinosaur (Yinlong downsi), one of the oldest tyrannosaurs (Guanlong wucaii), and several skeletons of an unusual, toothless new ceratosaurian dinosaur (Limusaurus inextricabilis) that were buried while stuck in mud pits.
To identify Haplocheirus as part of the family Alvarezsauroidea, Mr. Choiniere spent six months traveling to museums in Utah, New York, England, Spain, Mongolia and China to examine already indentified specimens and compare them with Haplocheirus. The identification process, he says, is “a series of small steps” involving careful analysis of bone features as well as a phylogenetic software analysis to determine evolutionary relationships.
Mr. Choiniere says he developed a “good feeling” about Haplocheirus’ connection to the family Alvarezsauroidea as he furthered his research. “It was really rewarding to have my anatomical observations confirmed by the data,” he says.
Mr. Choiniere, who joined Dr. Clark’s research team in 2004, has traveled to China six times for expeditions and research. On an average day in the field, he will walk 10 miles in the desert in up to 114-degree heat to look for fossils. Once one is discovered, the research team will cut a trench around the area to dig out the find and coat it in plaster and burlap to prepare it for transport to a laboratory—a process that can take anywhere from a few hours to weeks depending on the size of the find. In 2009, the team transported 80 of these pieces or “jackets” to Beijing.
Mr. Choiniere, who credits his love for science from a childhood growing up on a 1,400-acre wildlife sanctuary in Massachusetts, compares the paleontology expeditions to “fishing expeditions” in that there’s no guarantee what, if anything, researchers will find. “Sometimes you reel in something great, and sometimes you don’t find anything new,” he says. The mystery is compounded by the fact that the Xinjiang area of China contains fossils from a relatively unexplored time period, he says. “Most of the time, we have no idea what we’re going to find.”