Until 1909, naturalists grouped hippos with pigs, based on molar patterns. Several lines of evidence, first from blood proteins, then from molecular systematics and DNA and the fossil record, show that their closest living relatives are cetaceans - whales, dolphins and porpoises. The common ancestor of hippos and whales branched off from Ruminantia and the rest of the even-toed ungulates; the cetacean and hippo lineages split soon afterwards. Read more ...
Kenyan fossils show evolution of hippos Science Daily - February 24, 2015
A French-Kenyan research team has just described a new fossil ancestor of today's hippo family. This discovery bridges a gap in the fossil record separating these animals from their closest modern-day cousins, the cetaceans. It also shows that some 35 million years ago, the ancestors of hippos were among the first large mammals to colonize the African continent, long before those of any of the large carnivores, giraffes or bovines.
Million-Year-Old Fossils Show Hippos Going for a Swim Live Science - June 13, 2014
More than a million years ago, hippopotamuses paddled across a shallow pool in the region that's now northern Kenya, occasionally scraping their feet on the sandy bottom. Today, researchers have evidence of the hippos' fleeting swim in the form of fossilized footprints. The newly identified prints represent the first known tracks of ancient mammals taking a dip, joining previously discovered trace fossils left behind by swimming dinosaurs, turtles and crocodiles, the researchers said.
Signs of Arctic 'hippo' seen down mine News in Science - April 25, 2007
Fossils of a hippopotamus-like creature on an Arctic island show the climate was once balmy, giving clues to risks from modern global warming, a scientist says. Fossil footprints of a pantodont, a plant-eating creature weighing about 400 kilograms, add to evidence of sequoia-type trees and crocodile-like beasts in the Arctic millions of years ago when greenhouse gas concentrations in the air were high. The climate here about 55 million years ago was more like that of Florida Where we are now was once a temperate rainforest at the end of a horizontal mine shaft 5 kilometres inside a mountain and 300 metres below the surface. He points to a row of footprint impressions found in December in the roof of the mine north of Longyearbyen, the main settlement on the barren treeless Norwegian archipelago 1000 kilometres from the north pole.
Two miners found the footprints by chance. "As far as we know there are only five pantodonts of this type found in the world," says Steve Torgersen, a mining expert. Sluijs says forests grew in the Arctic when carbon dioxide, the main greenhouse gas, was at about 1000 parts per million in the atmosphere because of natural swings in the climate. The ancient warming was triggered by natural shifts, perhaps linked to volcanic activity and a thaw of frozen methane. And Sluijs says such high carbon dioxide concentrations point to risks with surging modern emissions stoked by human use of fossil fuels. "It's a worrying scenario for future global warming," he says. Sea levels 55 million years ago were about 100 metres higher than now and Antarctica was free of ice. "We are starting processes that will last for hundreds, perhaps thousands of years," he says of modern emissions from burning fossil fuels in power plants, factories and cars. When Svalbard was hot - the islands were also close to the North Pole 55 million years ago - many parts of the globe near the equator would have been too hot for modern plants and animals that have adapted to a modern climate, he says.
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