Mammal Evolution King ID'd

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Remains of the oldest ancestor of the most evolutionarily successful and long-lived mammal lineage have just been unearthed in China, according to a new study.

The mammal —  one of several creatures known as multituberculates – looked like a cross between a small rat and a chipmunk. It lived 160 million years ago during the Cretaceous era, according to the paper, published in the journal Science.

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This particular new species was Rugosodon eurasiaticus, which is the oldest known multituberculate. Its remains were found preserved in lake sediments, suggesting that it lived on the shores.

“The later multituberculates of the Cretaceous and the Paleocene are extremely functionally diverse: Some could jump, some could burrow, others could climb trees and many more lived on the ground,” explained Zhe-Xi Luo, a co-author of the paper. “The tree-climbing multituberculates and the jumping multituberculates had the most interesting ankle bones, capable of ‘hyper-back-rotation’ of the hind feet.”

China was a hotbed for dinosaurs during the Cretaceous, so one can imagine these little rodent-type animals scurrying around gigantic dinosaur legs, grabbing spilled food. Apparently these early mammals could eat almost anything that would fit into their mouths.

Its teeth were appropriate for gnawing on both plants and animals alike, revealing that it was an omnivore. Luo and colleagues believe that R. eurasiaticus was nocturnal and primarily lived on the ground. This makes its super-flexible ankles all the more surprising. Usually those are more associated with tree dwellers.

Multituberculate arose in the Jurassic period and went extinct in the Oligocene epoch. They occupied a diverse range of habitats for more than 100 million years before they were out-competed by more modern rodents.

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By the end of their run on the planet, multituberculates had evolved complex teeth, suitable for eating the toughest plants, and locomotive skills that enabled them to traverse treetops with ease.

No other mammal group has survived that long. Could humans/primates break the record? I very much doubt that, but we’ll see. We still have 99 million years plus of existence to beat out these prehistoric rat-like animals.

Like most early nocturnal mammals, Rugosodon eurasiaticus was active at night. This reconstruction shows Rugosodon searching for food among ferns and cycads on the lakeshores in the darkness; Credit: April Isch, University of Chicago 

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