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"Something must have happened to preserve these in the fossil record," said Prof Richard Butler, a palaeobiologist from the University of Birmingham.

"You can learn things about how that animal moved. You can learn exactly what the environment that it was living in was like. So tracks give us a whole different set of information that you can't get from the bone fossil record."

"In biological anthropology, we're always interested in finding new ways to extract behavior from the fossil record, and this is a great example," said Rebecca Ferrell, a program director at the National Science Foundation who helped fund this portion of the research.

The team assembled the largest-ever dataset of ancient human fossils spanning 7 million years and used advanced computational and statistical methods to account for gaps in the fossil record.

According to the fossil record, cetaceans -- whales, dolphins and their relatives -- evolved from four-legged land mammals that returned to the oceans beginning some 50 million years ago.