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It's called the latitudinal diversity gradient, a phenomenon seen today in most plant and animal species around the world: Biodiversity decreases from the equator to higher latitudes. A new study of fossils representing 63 million of the past 65 million years reveals that—for North American mammals, at least—the modern LDG is the exception rather than the rule

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The findings, reported in the Proceedings of the National Academy of Sciences, point to the importance of not assuming that the way things are today is the way they've always been, the researchers say

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The LDG says there are more species at the equator than at the poles," said Jonathan Marcot, a University of Illinois animal biology professor who conducted the study with David Fox and Spencer Niebuhr of the University of Minnesota. "This has been considered a first-order pattern of biodiversity, meaning one of the most general patterns in ecology. You find it in mammals, you find it in birds, you find it in insects, you find it in plants, you find it in the ocean and you find it on land

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The iTunes and Apple Stores used WebObjects -- and actually still use some of its code. A group of WebObjects developers still exist, even though Apple hadn't updated the software since 2008.If you go back a few thousand years ago, before we lost a lot of the large mammals that we had in North America, and probably for millions or tens of millions of years before this, we had horses in the higher latitudes, we had mammoths, we had rhinoceroses. Things that you find mostly in southern latitudes today, we had in northern latitudes as well," Marcot said.

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To answer this, the team turned again to the fossil record, this time looking at 27,903 fossil occurrences in all latitudes of North America representing 63 million years of mammalian life—from the time of the dinosaur extinctions to 2 million years ago. They compared mammalian species diversity at every latitude and every time period for which sufficient data were available. They also analyzed diversity in relation to the record of temperature changes over the same time period

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Porta fusce suscipit
Jan 11, 2014

What we found is that for most of the time that we considered, from 65 million years ago to about 10 million years ago, there was no strong evidence for a gradient," Marcot said. "There were roughly as many animal species in the northern parts of North America as there were in the southern regions

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Pellener tesque sed
Aug 19, 2015

The guy I spoke to called a couple of times, at first, he had absolutely no idea what WO was but the second time he called, he had obtained information and had a clear statement: 'WebObjects is a discontinued product and will never be upgraded.

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sit amet consectetur
sep 11, 2014

Between 10 million and 4 million years ago, "we start to see a strengthening of a gradient," he said. "And finally, we found strong evidence for a negative gradient—that is, more species in the south than in the north—starting around 4 million years ago

The team also analyzed the gradient in relation to the record of temperature changes over the same time period and found "a statistically significant correlation between temperature and the diversity gradient, meaning that the colder it gets, the stronger the diversity gradient gets for North American mammals," Marcot said.