Bi Discovers New Fossil Showing Mammals Appeared on Earth Earlier Than Scientists Thought; Study Published in ‘Nature’

Posted on 11/5/2013 2:21:20 PM

Arboroharamiya fossil found by Shundong Bi

Shundong Bi, associate professor of biology, has coauthored a fossil study that suggests mammals appeared 50 million years earlier than scientists thought. His research was published in the August 8, 2013, issue of Nature.

Dr. BiThe Discovery in the Drawer

Professor Shundong Bi, a paleontologist, stood in front of a cabinet filled with drawers lining one wall in the Shandong Tianyu Museum of Nature in Pingyi, China. He pulled open the drawers one by one and with a well-trained eye scanned hundreds of fossils gathered by local residents.

Something caught his attention: a rock showing the complete skeleton of a small animal.

"The moment I saw it, I thought, this is a big discovery," he recalls. "This is the specimen I want to work on."

Bi, on sabbatical, was serving as a visiting scholar at the Institute of Vertebrate Paleontology and Paleoanthropology. He spent many hours searching for fossils for his classroom teaching and research on mammals at IUP.

For the next year, Bi led a research team in an analysis of this fossil that resulted in their exciting discovery of an animal representing a new extinct genus of early mammal.

The previously unknown creature indicates that mammals appeared on Earth 50 million years earlier than scientists thought.

Bi and his team created a schematic skeleton of Arboroharamiya based on the fossilBringing a New Mammal up out of the Past

An expert in evolutionary biology, Bi focuses his research on the morphology, systematics, and functional anatomy of mammals, especially insectivores and rodents.

He and his team determined they were looking at the most complete fossil skeleton ever found of a member of the Haramiyida clade (evolutionary group) of mammals. Weighing in at 354 grams, it was also the largest.

Not much has been known about the haramiyids, because previous fossils have been mostly just teeth, Bi explains. This specimen provided information never before seen.

Through extensive analysis, Bi and his team concluded, moreover, that this was a new type of haramiyid, one that probably dwelled in trees. They named it Arboroharamiya jenkinsi.

The creature had small hands and feet but exceptionally long digits. Like an opossum with a prehensile tail, it may have been capable of wrapping its long tail around and grasping small twigs. Based on the shape of its teeth, it may have been an omnivore or a seed eater.

But their most dramatic finding was this: Arboroharamiya jenkinsi had a single lower jaw bone.

Leading the Science on When Mammals Originated

In fish and reptile species before their evolution into mammals, the middle ear bone was located close to the jaw.

Its absence from the jaw in Arboroharamiya implies a three-boned middle ear, says Bi. This is highly significant because it puts Arboroharamiya in the class of "crown mammals," or true mammals.

This means that mammals originated at least 215 million years ago, during the Triassic Period, over 50 million years earlier than the time in the Jurassic Period scientists have attributed mammal origins.

Bi’s findings were published in the August 8, 2013, issue of Nature.

Arboroharamiya with insect

The location of the middle ear bone is the telling detail in Arboroharamiya jenkinsi that times the origin of mammals on Earth about 50 million years earlier than scientists thought.

Bi feels drawn to China’s Gobi Desert region, which is known for its fossils of mammals and dinosaurs. He’s conducted research in museum settings and in the field, sifting sand to find tiny fossil rodent teeth.

“Every summer, I go back to China for field work,” Bi says. “I’ve collected lots of samples to use in my teaching."

For example, Bi and undergraduate biology honors student Sarah McLean recently finished fossil research and analysis indicating a new genus of mountain beaver. Their results were published in the journal PLOS, the Public Library of Science.

The Arboroharamiya specimen is, says Bi, "the biggest discovery in my career—so far."

—Marilyn Kukula and Deborah Klenotic