This ancient tadpole fossil is the oldest ever discovered

NEW YORK (AP) — Scientists have discovered the oldest-known fossil of a giant tadpole that wriggled around over 160 million years ago.

The new fossil, found in Argentina, surpasses the previous ancient record holder by about 20 million years.

Imprinted in a slab of sandstone are parts of the tadpole's skull and backbone, along with impressions of its eyes and nerves.

"It's not only the oldest tadpole known, but also the most exquisitely preserved," said study author Mariana Chuliver, a biologist at Buenos Aires' Maimonides University.

Researchers know frogs were hopping around as far back as 2...