As to what led to this continental-level decline, "there is a very large unknown looming here," MacPhee said. He does not think competition between the different mammoth populations is a likely culprit. Human over-hunting also does not make sense.
"You have humans in both Asia and North America at that time, but no drop-out in North America at that time," he added. "Disease of course immediately comes to mind, but we have nothing to go on for that yet."
Although the iconic mammoth of the Late Pleistocene, the woolly mammoth (Mammuthus primigenius), has traditionally been regarded as the end point of a single anagenetically evolving lineage, recent paleontological and molecular studies have shown that successive allopatric speciation events must have occurred within Pleistocene Mammuthus in Asia, with subsequent expansion and hybridization between nominal taxa [1, 2]. However, the role of North American mammoth populations in these events has not been adequately explored from an ancient-DNA standpoint. To undertake this task, we analyzed mtDNA from a large data set consisting of mammoth samples from across Holarctica (n = 160) and representing most of radiocarbon time. Our evidence shows that, during the terminal Pleistocene, haplotypes originating in and characteristic of New World populations replaced or succeeded those endemic to Asia and western Beringia. Also, during the Last Glacial Maximum, mammoth populations do not appear to have suffered an overall decline in diversity, despite differing responses on either side of the Bering land bridge. In summary, the ‘‘Out-of-America’’ hypothesis holds that the dispersal of North American woolly mammoths into other parts of Holarctica created major phylogeographic structuring within Mammuthus primigenius populations, shaping the last phase of their evolutionary history before their demise.
Last woolly mammoths had North American roots: study
Last Updated: Thursday, September 4, 2008 | 12:20 PM ET Comments26Recommend26
The last of the woolly mammoths to roam the Earth had North American ancestry, according to a study released Thursday by researchers at McMaster University in Hamilton.
The study, based on DNA of woolly mammoth specimens, is expected to cause some controversy among paleontologists, because it suggests that North American mammoths replaced their Eurasian counterparts. The study appears in the September issue of Current Biology.
Hendrik Poinar, associate professor in the departments of anthropology, and pathology and molecular medicine at McMaster University, said the results of the study are surprising.
"Scientists have always thought that because mammoths roamed such a huge territory, from western Europe to central North America, that North American woolly mammoths were a sideshow of no particular significance to the evolution of the species," he said.
"However, it now appears that mammoths established themselves in North America much earlier than presumed, then migrated back to Siberia, and eventually replaced all pre-existing haplotypes of mammoths."
Poinar said migrations over Beringia, the land bridge that once spanned the Bering Strait, were rare. "It served as a filter to keep eastern and western groups or populations of woollies apart," he said.
DNA evidence reveals ancestry
But the study shows that a migration of North American mammoths did occur. Woolly mammoths lived between 40,000 and 4,000 years ago.
Poinar and Regis Debruyne, a post-doctoral research fellow in Poinar's lab, spent three years collecting and sampling mammoths from much of their former range in Siberia and North America. They extracted DNA and pieced together the samples, comparing and studying hundreds of mammoth specimens using a database of ancient DNA.
Debruyne said the study shows that North American mammoths were more important in evolutionary terms than previously considered by scientists.
"Like paleontologists, molecular biologists have long been operating under a geographic bias," he said.
"For more than a century, any discussion on the woolly mammoth has primarily focused on the well-studied Eurasian mammoths. Little attention was dedicated to the North American samples, and it was generally assumed their contribution to the evolutionary history of the species was negligible. This study certainly proves otherwise."