Museum Curator Bones Up on His Extinction Theory

Ross MacPhee opened a clear plastic vial that held what looked like finely grated cheese.

Take a whiff, he said.

Two young visitors to his office at the American Museum of Natural History sniffed, wrinkled their faces and turned away from the rancid stench.

No doubt about it. Bone marrow from woolly mammoths really stinks.

But for MacPhee, who’d just returned from Siberia with three dozen vials of ancient bone samples, this scent may lead to a sweet reward: hard evidence for his theory of why mammoths and many other species of big mammals in North and South America disappeared about 13,000 years ago.

MacPhee, curator of mammalogy at the museum, counts 135 species that disappeared from the Americas. The North American losses include mastodons, camels, lions, cheetahs, saber-tooth cats, horses and giant sloths as big as buffalo.

What caused this? Debate has gone on for decades, centering mostly on two possible explanations: climate change and voracious hunting by newly arrived humans.

MacPhee didn’t buy either idea.

Mammals had survived much bigger climate changes before, and how could a general phenomenon like climate kill animals from Alaska to Tierra del Fuego within a few centuries without bothering others in the West Indies at the same time?

The over-hunting idea made no sense to him either. The early Americans were too sparse and ill-equipped to drive so many mammals to extinction, he reckoned.

MacPhee got into the debate after reading a magazine article about Ebola virus, the highly lethal germ that infects people. He began to wonder: Could viruses have arrived in the Americas with early humans or accompanying animals like wolf-dogs and scavenging rodents and birds? And could they have then jumped into a wide variety of mammals that had no natural defenses, causing a bunch of diseases that wiped out whole species?

MacPhee and virus expert Preston Marx developed this “hyperdisease” idea and published it in 1997.

“I don’t give it much chance,” said Paul S. Martin, an emeritus professor in geosciences at the University of Arizona. But the proposal is worth considering, he said.

MacPhee cheerfully admits he doesn’t have a whit of direct evidence yet for his idea. Nor is it clear what diseases are vicious enough to have done the job.

The search for direct evidence to support the hyperdisease explanation began earlier this year, when MacPhee’s colleague Alex Greenwood started looking for traces of viruses in ancient mammal bones.

The quest for more samples sent MacPhee in August to Siberia, where mammoths appear to have died out at about the same time as in North America.

He joined other scientists and a group of local fishermen in strolling the tundra near Lake Taimyr, between the Kara and Laptev seas. They looked along river banks for exposed bones of mammoths and other big mammals.

MacPhee used a cordless drill to extract tissue samples the size of wine corks from these bones, including specimens like a 3.5-foot hipbone from a mammoth that stood 8 feet tall at the shoulder.

It’ll take a long time to uncover and recognize any trace of a killer virus, if it’s there to be found at all. In the meantime, MacPhee says he’s not staking his career on the hyperdisease idea.

“If something better comes along tomorrow, it’s dead meat,” he said. But “right now I don’t know what’s much better.”