NEW YORK – Since the extinction of the mammoths and mastodons some 12,000 years ago, the only animals with trunks and tusks in North America have been those brought here to perform in circuses or to live in zoos. But two prominent ecologists want that to change. David Burney, a Fordham associate professor of biological sciences, and Paul Martin, who recently retired from the University of Arizona, want to bring a herd of African and Asian elephants to North America to replace their extinct relatives. In 1999, Burney and Martin published, “Bring Back the Elephants!” in the respected conservation journal Wild Earth. In it, they described their vision of thousands of elephants roaming the grasslands of the West a century or two from now. Mammoths and mastodons arrived in North America tens of millions of years ago. They even roamed Manhattan, where mastodon bones are often found when the Harlem River Canal is dredged. Their disappearance was part of a wider extinction that wiped out three-quarters of the large mammals in North America. Burney and Martin, who have both spent their careers studying prehistoric ecosystems, believe that humans caused the animals’ extinction. So, as they see it, humans ought to do what they can to replace the animals with their closest living relative: the elephant. The ecologists believe that the trunked herbivores would do well in western climates because they can tolerate a wide range of environments. The elephants would have plenty to eat in the West, which is overrun with shrubs and small trees because of a lack of shrub-eating animals. A herd of elephants would solve that problem, as they consume 400 pounds of thorny plants, brush and small trees every day. Should their plan come to fruition, Burney says the first transplants should be Indian elephants because they are smaller and more manageable than their African counterparts. The ecologists suggest starting with about a dozen elephants in an area between 50 and 400 square miles. Burney and Martin say tracts of Nevada, Arizona and New Mexico would be ideal because their remote grasslands, usually seen as unproductive, could feed the animals well.