Alaska: Genome analysis pins down arrival and spread of first Americans; Comparing current and ancient genomes shows Siberian migration no earlier than 23,000 years ago - The original Americans came from Siberia in a single wave no more than 23,000 years ago, at the height of the last Ice Age, and apparently hung out in the north - perhaps for thousands of years - before spreading in two distinct populations throughout North and South America, according to a new genomic analysis.

This is an artist's representation of the ice age landscape that early Native Americans would have encountered.
Artwork by Sussi Bech

The findings, which will be reported in the July 24 issue of Science, confirm the most popular theory of the peopling of the Americas, but throws cold water on others, including the notion of an earlier wave of people from East Asia prior to the last glacial maximum, and the idea that multiple independent waves produced the major subgroups of Native Americans we see today, as opposed to diversification in the Americas.

"Our study presents the most comprehensive picture of the genetic prehistory of the Americas to date. We show that all Native Americans, including the major sub-groups of Amerindians and Athabascans, descend from the same migration wave into the Americas. This was distinct from later waves that gave rise to the Paleo-Eskimo and Inuit populations in the New World Arctic region," says Dr. Maanasa Raghavan, a postdoctoral researcher at the Centre for GeoGenetics and one of the lead authors of the study.

"We applied several statistical methods that differ in modeling or utilize different information in the data. That we obtained consistent results across different methods is significant and reassuring," says Professor Yun Song at UC Berkeley, a co-author of the study.

Since Amerindians and Athabascans were part of the same migration into the Americas, the current genetic differences observed between them would have emerged sometime after 23,000 years ago.

This Ice Age migration over a land bridge between Siberia and Alaska is distinct from the arrival of the Inuit and Eskimo, who were latecomers, spreading throughout the Artic beginning about 5,500 years ago.

The findings also dispel the idea that Europeans contributed to the genetic heritage of Native Americans.

Modern and ancient genomes

The data consisted of the sequenced genomes of 31 living Native Americans, Siberians and people from around the Pacific Ocean, and the genomes of 23 ancient individuals from North and South America, spanning a time between 200 and 6,000 years ago.

"There is some uncertainty in the dates of the migration and the divergence between the norther and southern Amerindian populations," Song noted, "but as we get more ancient genomes sequenced, we will be able to put more precise dates on the times of migration."

The international team concluded that the northern and southern Native American populations diverged between 11,500 and 14,500 years ago, with the northern branch leading to the present day Athabascans and Amerindians broadly distributed throughout North America. The southern branch peopled Central and South America, as well as part of northern North America.

"The diversification of modern Native Americans appears to have started around 13,000 years ago when the first unique Native American culture appears in the archeological record: the Clovis culture," said Nielsen. "We can date this split so precisely in part because we previously have analyzed the 12,600-year-old remains of a boy associated with the Clovis culture."

One surprise in the genetic data is that both populations of Native Americans have a small admixture of genes from East Asians and Australo-Melanesians, including Papuans, Solomon Islanders and Southeast Asian hunter gatherers.

"It's a surprising finding and it implies that New World populations were not completely isolated from the Old World after their initial migration," said Eske Willerslev from the Centre for GeoGenetics at the Natural History Museum, University of Copenhagen, who headed the study. "We cannot say exactly how and when this gene flow happened, but one possibility is that it came through the Aleutian Islanders living off the coast of Alaska." - More...
Wednesday PM - July 22, 2015

Alaska: First elasmosaur specimen excavated in Alaska By THERESA BAKKER - A recent expedition to the Talkeetna Mountains by the University of Alaska Museum of the North has uncovered a new marine reptile fossil from the Age of Dinosaurs known as an elasmosaur.

An articulated portion of the spine extends into the hill to the right of the small plaster jacket. The larger plaster jacket contains part of the elasmosaur’s scapula.
Photo by Pat Druckenmiller

Earth sciences curator Patrick Druckenmiller said elasmosaurs are a type of plesiosaur with extremely long necks and two pairs of paddle-like limbs used to swim under water. They lived during the Late Cretaceous period about 70 million years ago. “Picture the mythical Loch Ness monster and you have a pretty good idea what it looked like. This is an exciting find because it is the first time an elasmosaur has ever been discovered in Alaska.”

Over the past few years, Curvin Metzler, an Anchorage-based fossil collector, found several vertebrae from the skeleton eroding out of a bluff. He’d been hiking in the area for 25 years and this was the first vertebrate fossil he found there. When Metzler, Druckenmiller and two others visited the site in June, they were able to identify the source of the bones in the hillside and collect a good portion of the skeleton.

“I’m mostly interested in finding invertebrates, so when I saw the first vertebra I knew it was a bone from something,” Metzler said. “I didn’t want to disturb anything in the cliff so it was exciting to talk to Pat. We are lucky to have someone in the state who works with fossils.”

Even though the new elasmosaur is a first for the state, Druckenmiller has collected plesiosaurs from all over western North American and is one of the world’s marine reptile fossil experts. In 2010, he led a team that collected a nearly complete elasmosaur skeleton from Montana, which is currently on display as part of the museum’s “Expedition Alaska: Dinosaurs” exhibit in Fairbanks.

“I was really excited the first time Curvin showed me one of its bones,” he said. “I recognized it as a vertebra from the base of the animal’s neck and wanted to visit the site to see if we could find more. Based on the size of the bones we excavated, the animal should be at least 25 feet long.” - More...
Wednesday PM - July 22, 2015