Snakes, with their sleek bodies and diversity, have long entranced humans. But we know very little about the evolutionary past of these legless lizards because of a scarcity of fossils left by snake ancestors that shared Earth with dinosaurs.

That’s why excavated snake fossils from Argentina, described in a study published in Science Advances, are such a big deal. The intricate fossils, mostly skulls, are nearly 100 million years old and belong to the extinct snake group Najash, which still retained hind legs. Scientists have not found fossils of the snake family’s four-legged ancestors. But the study suggests that those mysterious proto-snakes probably lost their forelimbs early in snake evolution, at least 170 million years ago. But the back legs stuck around for tens of millions of years.

That means that hind-legged snakes, such as the Najash group, did not represent a short-lived evolutionary phase. Instead, snakes retaining two of their legs lived for eons until most snakes transitioned into fully limbless slitherers in the latter half of the Cretaceous period.

Discovery may help reveal tie between wolves, dogs

An 18,000-year-old puppy buried for centuries in a lump of frozen mud was unveiled by scientists who hope it can help bridge the connection between dogs and wolves.

The male puppy was discovered in permafrost in Siberia, said Dave Stanton, a research fellow at the Center for Palaeogenetics in Stockholm. The fur, skeleton, teeth, head, lashes and whiskers of the pup are still intact, he said. But scientists don’t know whether it is a dog or wolf. Stanton said more DNA research would be conducted.

Many scientists say dogs evolved about 15,000 years ago from a species of extinct wolves. Others suggest it could have happened much earlier, perhaps 30,000 years ago or more. Several extinct animals have been found in the thick permafrost, in part because of the melting of ice resulting from climate change.

“It must have frozen quickly before scavengers could get to it,” Stanton said of the puppy.

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