Scientists believe they have unravelled the mystery behind a graveyard of whales dating back five million years uncovered beside the Pan-American Highway in Chile.
A report published today in the Royal Society Journal B suggests the animals, which are one of the most astonishing fossil discoveries in recent years, may have died in four mass strandings after ingesting toxic algae.
The animal carcasses are then thought to have washed into an estuary before becoming buried by sand over time, preserving the fossils.
Northern Chile’s Atacama Desert is well known for preserving whale fossils after the site was discovered during an expansion project of the Pan-American Highway in 2010. Bones could be seen sticking out of rock faces, leading many to nickname the spot Cerro Ballena, or "whale hill", as a result.
American and Chilean paleontologists were finally given the opportunity to examine properly the fossil beds when a cutting was made to widen the Highway in 2011.
A team from the Smithsonian’s National Museum of Natural History and Chilean scientists had just two weeks to undertake their investigations before the heavy plant returned to complete construction of the new road, according to the BBC.
In pictures: 12 amazing archaeological discoveries
In pictures: 12 amazing archaeological discoveries
1/12 Ancient forest, discovered in February 2014
Ancient forest revealed by storms. The recent huge storms and gale force winds that have battered the coast of West Wales have stripped away much of the sand from stretches of the beach between Borth and Ynyslas. The disappearing sands have revealed ancients forests, with the remains of oak trees dating back to the Bronze Age, 6,000 years ago. The ancient remains are said by some to be the origins of the legend of ‚Cantre‚r Gwealod‚ , a mythical kingdom now submerged under the waters pif Cardigan Bay
2/12 Medieval royal palaces, discovered in November 2014
Archaeologists in southern England have discovered what may be one of the largest medieval royal palaces ever found – buried under the ground inside a vast prehistoric fortress at Old Sarum. The probable 12th century palace was discovered by archaeologists, using geophysical ground-penetrating ‘x-ray’ technology to map a long-vanished medieval city which has lain under grass on the site for more than 700 years
3/12 The Dead Sea Scrolls, discovered ca. 1950
The Dead Sea Scrolls are almost 1,000 biblical manuscripts discovered in the decade after the Second World War in what is now the West Bank. The texts, mostly written on parchment but also on papyrus and bronze, are the earliest surviving copies of biblical and extra-biblical documents known to be in existence, dating over a 700-year period around the birth of Jesus. The ancient Jewish sect the Essenes is supposed to have authored the scrolls, written in Hebrew, Aramaic and Greek, although no conclusive proof has been found to this effect
4/12 Diamond, discovered in March 2014
This rare diamond that survived a trip from deep within the Earth's interior confirmed that there is an ocean’s worth of water beneath the planet’s crust
Richard Siemens/University of Alberta
5/12 Whale skeletons, discovered in February 2014
Chilean and Smithsonian paleontologists study several fossil whale skeletons at Cerro Ballena, next to the Pan-American Highway in the Atacama Region of Chile
6/12 Complete mammoth skeleton, discovered in November 2012
The first complete mammoth skeleton to be found in France for more than a century was uncovered in a gravel pit on the banks of the Marne, 30 miles north-east of Paris. Picture shows experts at work making a silicon cast of the mammoth's tusk
7/12 Million-year-old human footprints, discovered in February 2014
Photograph of the footprint hollows in situ on the beach as Happisburgh, Norfolk
8/12 Terracotta warrior, discovered in June 2010
Chinese archaeologists unearthed around 120 more clay figures in June 2010 excavations at the terracotta army site that surrounds the tomb of the nation's first emperor in the northwestern Shaanxi Province
© Jason Lee / Reuters
9/12 Neolithic 'lost avenue' - prehistoric stone circle, discovered in September 1999
The discovery of a Neolithic 'lost avenue' was described as one of the most important finds of the last century. Since the 1700s, archeologists and historians have argued over the existence of the huge sarsen stones, which were unearthed at the site of the world's biggest prehistoric stone circle at Avebury in Wiltshire
10/12 Byzantine mosaic, discovered in February 2007
Plans for a walkway at the centre of the furious dispute over Jerusalem's holiest site were delayed by the discovery of a Byzantine mosaic
11/12 Ancient gold, discovered in March 2014
Gold fitting for a dagger sheath (around 1900 BC.) found near Stonehenge
12/12 Rosetta Stone, discovered in 1799
The Rosetta Stone is a basalt slab inscribed with a decree of pharaoh Ptolemy Epiphanes (205-180 BC) in three languages, Greek, Hieroglyphic and Demotic script. Discovered near Rosetta in Egypt
The team recorded as much detail as possible and created 3D models of the skeletal remains in situ. They also removed some bones from the site to study further in the lab.
In addition to the skeletons of more than 40 large baleen whales that dominated the site, the team documented the remains of an extinct walrus-like whale – dolphins which evolved a walrus-like face – and found skeletons of billfishes, seals and aquatic sloths.
"To me, it's amazing that in 240m of road-cut, we managed to sample all the superstars of the fossil marine-mammal world in South America in the Late Miocene. Just an incredibly dense accumulation of species," Nicholas Pyenson, a palaeontologist at the Smithsonian, told the BBC.
The team also noted how the carcasses were arranged. The skeletons, which were nearly all complete, were preserved in four separate levels, pointing to a repeated and similar underlying cause of death. But the different fossil levels suggested it was not one event but four separate episodes spread over a period of several thousand years.
From their research, the scientists concluded toxins generated by harmful algal blooms are likely to have poisoned the animals. If the algae were inhaled or large quantities of contaminated prey consumed, death would have been rapid.
"All the creatures we found - whether whales, seals or billfishes - fed high up in marine food webs and that would have made them very susceptible to harmful algal blooms," Dr Pyenson said.
The bodies would then have been funnelled into a restricted area by the coastline at Cerro Ballena in the late Miocene period (five to 11-million-years-ago). Once stranded on the tidal flat, the dead or dying animals would have been protected from marine scavengers.
However, the team could not say for certain that harmful algal blooms were responsible for the mass strandings, as there were no distinct algal cell fragments present in the sediments. They did find multiple grains encrusted in iron oxides that could suggest past algal activity.
Dr Pyenson added: "They're found in algal-like mats all around the site. We can't say whether those were the killer algae, but they do not falsify the argument for harmful algal blooms being the cause in the way that the sedimentology falsifies tsunami being a potential cause."