This video says about itself:
26 November 2011
From Wildlife Extra:
Ancient marine graveyard mystery solved
The marine graveyard was discovered in 2011 when builders working to extend the Pan-American Highway discovered a 250 metre wide quarry site filled with the skeletons of more than 40 marine mammals including 31 large baleen whales, seals, a walrus-like toothed whale, an aquatic sloth and an extinct species of sperm whale, suggesting that they died from the same cause.
The wide array of animals buried at the site over four levels indicated that the cause of death didn’t differentiate between the young and old or between species, and occurred repeatedly over thousands of years. This suggests that harmful algae blooms, which cause organ failure, could be the most common cause of mass strandings.
Other causes, like tsunamis, were ruled out by the team of Chilean and Smithsonian paleontologists because they would have produced a range of skeletons including much smaller species, rather than the primarily large mammals found at Cerro Ballena. A mass stranding while alive was ruled out as a cause of death due to the way all the marine mammals were were found at right angles to the direction that the current would have flowed.
Humans have been using echolocation in the form of sonar since the early part of the 20th century, but whales have made use of the ability to use sound to pinpoint locations for tens of millions of years. As evidenced in the fossils – which belong to a new species of ancient whale named Cotylocara macei – cetaceans have been using echolocation for at least 30 million years: here.
Fossil algae reveal 500 million years of climate change: here.