March 30, 2015 at 5:41 am (mammals, paleontology, Prehistoric Life series)
Tags: Ardipithecus ramidus, Australopithecus, Clovis culture, Denisovan, evolution, human evolution, literature review, Neandertal, Pleistocene, Pliocene
by Carl Strang
Human. Photo by Linda Padera.
Kimbel, William H., et al. 2014. Ardipithecus ramidus and the evolution of the human cranial base. Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1322639111 From a ScienceDaily article. The base of this skull of the 3.4-million-year-old species Ardipithecus ramidus places it in the Australopithecus-human line and separates it from chimpanzees and other apes. The shape features may reflect a change to a more upright posture, or the early reorganization of the brain. Earlier studies had indicated that Ardipithecus was arboreal but also could walk upright on the ground.
Ashton, N., et al. 2014. Hominin footprints from Early Pleistocene deposits at Happisburgh, UK. PLoS ONE 9(2): e88329. doi:10.1371/journal.pone.0088329 They describe footprints of hominins estimated to be 850,000 years old, in sediments of an age where flint tools have been found, and establishing the earliest evidence of hominins outside of Africa. A combination of pollen analysis and stratigraphy (e.g., the footprints are beneath glacial sediments) established the age.
Vernot, Benjamin, and Joshua M. Akey. 2014. Resurrecting surviving Neandertal lineages from modern human genomes. Science 343:1017-1021. Gibbons, Ann. 2014. Neandertals and moderns made imperfect mates. Science 343:471-472. The Gibbons article is a news review describing Vernot and Akey’s study, which showed that though Neandertals and modern humans interbred, there were costs to the hybridization. Only a small amount of Neandertal genetic material has persisted in Europeans and East Asians as a result, mainly genes connected with keratin function, and so affecting skin color, waterproofing, and resistance to cold, helping modern humans to survive in more northern latitudes. They looked at whole genomes of several hundred European and Asian people, and found that collectively they preserve about 20% of the Neanderthal genome (each individual has only 1-3%).
Huerta-Sánchez, Emilia, et al. 2014. Altitude adaptation in Tibetans caused by introgression of Denisovan-like DNA. Nature, DOI: 10.1038/nature13408 From a ScienceDaily article. They looked at the genetics of these high altitude dwellers, and found that the main adaptation that allows them to live in low oxygen without heart problems comes from a gene their ancestors got through the Denisovans. The individuals who first moved into the area had some in their number descended from a modern human-Denisovan cross, and those people had a selective advantage in that environment.
Rasmussen, Morten, et al. 2014. The genome of a Late Pleistocene human from a Clovis burial site in western Montana. Nature 506 (7487): 225. DOI: 10.1038/nature13025 They worked up the genome of the only skeleton ever found in association with Clovis tools, that of a boy less than 2 years old found in a burial. His family and relatives are found to be ancestral to all Native Americans, and connected to Asian ancestors. The boy shares about 1/3 of his genes with the Baikal boy whose genome was sequenced in 2013, with the rest coming from east Asians, that blend happening before emigrating across the Bering Sea land bridge. The Clovis culture developed after the people were established in the New World, well before the 12,600-year age of the newly sequenced genome.
April 2, 2012 at 6:20 am (archeology, mammals, paleontology, Prehistoric Life series)
Tags: brown bear, caribou, Clovis culture, continental glacier, elk-moose, literature review, mastodon, megafauna, Pleistocene, polar bear, stag moose
by Carl Strang
The following notes complete my review of last year’s scientific literature. These studies looked at the most recent epoch, the Pleistocene, and focus on the megafauna, the large mammals.
Mastodon fossil, an iconic megafaunal species
Edwards, Ceiridwen J., et al. Ancient Hybridization and an Irish Origin for the Modern Polar Bear Matriline. Current Biology, 07 July 2011 DOI: 10.1016/j.cub.2011.05.058 As described in a ScienceDaily article. This new mitochondrial DNA study places the female ancestor of all current polar bears in Ireland 50,000 years ago, at the peak of the last ice age. Brown and polar bears once were both circumpolar, or nearly so, and the ebb and flow of the glaciers brought them in and out of contact, providing hybridization opportunities. The authors mention that this continues today, with the retreat of polar ice bringing the two species more into contact, and several recent hybrid individuals are known. The researchers indicate that this process needs to be taken into consideration both in understanding the nature of these species and in conservation planning.
Long, Charles A., and Christopher J. Yahnke. 2011. End of the Pleistocene: elk-moose (Cervalces) and caribou (Rangifer) in Wisconsin. J. Mammal. 92:1127-1135. They describe the northernmost caribou fossils found to date in Wisconsin, from Marathon County. The Cervalces (also known as stag moose) from the same site is the first for the state, and northernmost for the species. The study location was at the boundary between the glacier’s Green Bay Lobe and the driftless area. The age of the caribou antler is placed at 11,260-11,170 years ago. The elk-moose was from 12,920-12,790 years ago. The caribou probably was of the more southern woodland caribou species. The older elk-moose fossil was found in a sediment layer suggesting it lived close to the edge of the glacier, in more of a tundra environment.
Eline D. Lorenzen, et al. Species-specific responses of Late Quaternary megafauna to climate and humans. Nature, 2011; DOI: 10.1038/nature10574 As described in a ScienceDaily article. They looked at a range of genetic, archeological and other evidence, and found that the megafauna that went extinct and those that survived in the northern hemisphere represent a complex picture. All had survived previous glacial cycles by finding refugia in warm periods, with populations just large enough to continue. Some were able to do so again after the most recent glacial retreat, for instance caribou and musk oxen in the far north and bison in the North American plains, and survive to this day. Others did not, and in at least most of these cases humans are implicated, either by preventing retreat to refugia or by decimating the reduced populations.
Waters, Michael R., et al. 2011. Pre-Clovis mastodon hunting 13,800 years ago at the Manis site, Washington. Science 334:351-353. (also interpreted in a news article on p. 302 of the same issue). They found a spear point made of mastodon bone, imbedded in the rib of an adult male mastodon. It is dated to several hundred years before the Clovis culture. The location near the coast in Washington State is consistent with a coastal spread of people from Beringia, where bone spear points also were used. This also supports an extended period of megafauna hunting, further pointing toward human hunting as a factor in extinctions (a long period of hunting, even if it only removes animals slightly faster than they can reproduce, increases the importance of that mortality factor).