麻豆淫院

Long before the construction of the Felipe 脕ngeles International Airport, which lies northeast of Mexico City, the area was home to the former Lake Xaltocan and inhabited by a rich ecosystem of prehistoric animals. Eons later, in 2019, the somewhat controversial construction of the airport began, which led to the unearthing of at least 110 individual mammoths, as well as many other animal fossils.

Paleontologists assumed that these mammoths would be genetically the same or very similar to the Columbian mammoth (Mammuthus columbi)鈥攖he only species of mammoth native to North and Central America. The other species of mammoth found in North America is the woolly mammoth (Mammuthus primigenius), which clearly migrated from the Eurasian continent and has been mostly found in Canada and the United States. However, the origins of the Columbian mammoth are less clear.

Past research suggests that the Columbian mammoth may have arisen from the hybridization between woolly mammoths and another Eurasian species, the steppe mammoth (Mammuthus trogontherii) sometime around 800,000-400,000 years ago. It seemed likely that these mammoths were the same as those found in Mexico.

However, a new study, in Science paints a different picture by analyzing the mitochondrial DNA of the mammoths found during the construction of the Felipe 脕ngeles International Airport, along with samples from mammoths excavated between 2016 and 2019, at a site in nearby Tultepec.

Most often, extracting usable DNA for analysis in the tropics is difficult, since DNA doesn't typically fare well in warmer climates. This is in contrast with the many woolly and steppe mammoth DNA samples found in the far north. Therefore, most prior Columbian mammoth DNA came from fossils found in more northerly regions of North America. Using mitochondrial DNA extracted from the teeth, instead of nuclear DNA, was a way around this issue, although only the maternal lineage could be studied this way, which may not reflect the nuclear genome diversity.

The study revealed a distinct mitochondrial lineage of the Mexican mammoths, referred to as Clade 1G, separate from other North American mammoths. There were also further groupings within Clade 1G. The groupings within the Mexican group showed deeper genetic divergence than expected, with the divergence within Clade 1G being as great as the divergence between other major North American mammoth lineages.

The authors offer two explanations for these results. "First, there could have been structure at the mitochondrial level in the ancestral population of M. primigenius before the hybridization event with the M. trogontherii-like Krestovka lineage that gave rise to M. columbi. Second, this pattern could indicate different M. primigenius parental populations admixing at different times, with a similar M. trogontherii-like Krestovka lineage, giving rise to divergent M. columbi mitogenomes."

The study authors note that they lean toward the first explanation being the correct one. The researchers also used radiocarbon dating to determine the ages of the fossils, which suggested that these divergent lineages coexisted during the Late Pleistocene, between 40,000鈥�12,700 years ago.

The study has finally shed a bit more light on a previously difficult to analyze species. They say, "This study emphasizes the importance of recovering ancient genomic data from wider geographical ranges in order to fully understand the evolutionary trajectory of extinct species, and demonstrates the feasibility of recovering DNA from Late Pleistocene samples from tropical latitudes."

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