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A couple of years ago a large number of fossilized skeletons of whales that died between 6 and 9 mya (Late Miocene) were discovered in the Atacama Desert of Northern Chile at a site called Cerro Ballena (which is Spanish for "whale hill")[1] merely 240 meters long by 20 meters wide (787½' x 65½') while workers were widening the Pan American Highway.
The whales, many of which were found in excellent states of preservation, were uncovered in four distinct layers indicating that there were four separate strandings over a period of between 10,000 to 16,000 years. While this was a treasure trove for paleontologists it did create a mystery -- namely what killed these whales. The skeletons' orientation and condition along with an examination of a high resolution 3-D reconstruction of the site and all its fossils indicated that the animals died at sea, prior to burial on a tidal flat.
One early suspect was some sort of virus but this possibility was eliminated because they are unlikely to kill such a wide variety of species including both mammals and birds. The site contains the skeletons of nearly 40 large baleen whales but other creatures were discovered along with them including an extinct species of sperm whale, a "walrus whale" (a dolphin with walrus-like tusks), two seals (one of which was a previously unknown species), an aquatic sloth, several billfish and a penguin.
Another possibility was a tsunami which can also produce mass strandings but a close analysis revealed no evidence for a tsunami.
After examining the evidence a team led by Nicholas Pyenson, paleontologist at the Smithsonian's National Museum of Natural History, came to the conclusion that there is only one cause that fits all the available evidence -- that these animals were poisoned by toxins. The researchers think that the animals ate toxic algae before being washed into an estuary and eventually on to flat sands.
In modern settings, because they cause organ failure in marine mammals through ingestion of contaminated prey or inhalation, toxins from harmful algal blooms (HABs) such as red tides are the most prevalent cause for repeated mass die-offs or strandings for a wide variety of large marine animals. Further, HABs are the only known natural cause for such repeated, multi-species accumulations such as that seen at Cerro Ballena.
As Pyenson explained, "Harmful algal blooms in the modern world can strike a variety of marine mammals and large predatory fish. The key for us was its repetitive nature at Cerro Ballena: no other plausible explanation in the modern world would be recurring, except for toxic algae, which can recur if the conditions are right."
He pointed to a case in the late 1980s near Cape Cod, Massachusetts where over a dozen humpback whales washed ashore in a similar fashion to the way the fossils appear to have piled up in Chile and that had been poisoned by mackerel loaded with toxins from red tides as just one modern example.
Deadly algal blooms are common along the coasts of continents where they are enhanced by nutrients such as iron, which are released during erosion and washed into the oceans by rivers causing the formation of thick mats of plankton. Since the Andes Mountains are iron-rich, the runoff that has occurred along the west coast of South America has long provided ideal conditions for harmful algal blooms to form for millions of years.
The researchers say that taphonomic analysis reveals that toxins generated by HABs poisoned the whales and other ocean-going vertebrates, killing them fairly quickly[2]. Their carcasses then floated toward the coast where they were washed into a barrier-protected tidal flat by waves where they were protected from marine scavengers. The fact that there were no large terrestrial scavengers in South America at this time also allowed the bodies to remain unmolested as they were buried by sand.
Support for the conclusion that HABs were the cause of the deaths was provided by the discovery of orange splotches in the rock surrounding many of the skeletons that they thought were left by the chemical degradation of the algal mats. Examination of these splotches under a high-power microscope revealed tiny spheres similar to those found in dinoflagellates -- the plankton responsible for producing red tides.
Still, due to their degragation over millions of years it is not possible to definitively confirm that they came from a species associated with harmful algal blooms. As Pyenson noted, "It's a good candidate, but we can't exclude the possibility that these have a geological origin."
The results of the research were published today in the science journal "Proceedings of the Royal Society B"
1. about a kilometer (a little more than a half mile) from the current Pacific shoreline of the Pacific Ocean roughly 708 km (440 miles) or so north of the Chilean capital Santiago.
2. This is supported by the high percentage of the skeletons which were found belly-up which means they were already dead when they washed ashore rather than beaching themselves.
Further Reading:
Repeated mass strandings of Miocene marine mammals from Atacama Region of Chile point to sudden death at sea Abstract & Paper
Whale graveyard reveals most ancient mass strandings
Smithsonian scientists solve 'sudden death at sea' mystery
Ancient Whale Graveyard Discovered in Chile, Solves Mystery of Sudden Death at Sea
The Tiny Culprit Behind A Graveyard of Ancient Whales
Chile's stunning fossil whale graveyard explained
Whale graveyard shows mass stranding of species millions of years ago
Mystery of Atacama Desert whale graveyard solved
Killers Were Tiny, Victims Were Huge At Chile's Whale Graveyard
Chile's stunning fossil whale graveyard explained Short video
Excellent images from the site
The whales, many of which were found in excellent states of preservation, were uncovered in four distinct layers indicating that there were four separate strandings over a period of between 10,000 to 16,000 years. While this was a treasure trove for paleontologists it did create a mystery -- namely what killed these whales. The skeletons' orientation and condition along with an examination of a high resolution 3-D reconstruction of the site and all its fossils indicated that the animals died at sea, prior to burial on a tidal flat.
One early suspect was some sort of virus but this possibility was eliminated because they are unlikely to kill such a wide variety of species including both mammals and birds. The site contains the skeletons of nearly 40 large baleen whales but other creatures were discovered along with them including an extinct species of sperm whale, a "walrus whale" (a dolphin with walrus-like tusks), two seals (one of which was a previously unknown species), an aquatic sloth, several billfish and a penguin.
Another possibility was a tsunami which can also produce mass strandings but a close analysis revealed no evidence for a tsunami.
After examining the evidence a team led by Nicholas Pyenson, paleontologist at the Smithsonian's National Museum of Natural History, came to the conclusion that there is only one cause that fits all the available evidence -- that these animals were poisoned by toxins. The researchers think that the animals ate toxic algae before being washed into an estuary and eventually on to flat sands.
In modern settings, because they cause organ failure in marine mammals through ingestion of contaminated prey or inhalation, toxins from harmful algal blooms (HABs) such as red tides are the most prevalent cause for repeated mass die-offs or strandings for a wide variety of large marine animals. Further, HABs are the only known natural cause for such repeated, multi-species accumulations such as that seen at Cerro Ballena.
As Pyenson explained, "Harmful algal blooms in the modern world can strike a variety of marine mammals and large predatory fish. The key for us was its repetitive nature at Cerro Ballena: no other plausible explanation in the modern world would be recurring, except for toxic algae, which can recur if the conditions are right."
He pointed to a case in the late 1980s near Cape Cod, Massachusetts where over a dozen humpback whales washed ashore in a similar fashion to the way the fossils appear to have piled up in Chile and that had been poisoned by mackerel loaded with toxins from red tides as just one modern example.
Deadly algal blooms are common along the coasts of continents where they are enhanced by nutrients such as iron, which are released during erosion and washed into the oceans by rivers causing the formation of thick mats of plankton. Since the Andes Mountains are iron-rich, the runoff that has occurred along the west coast of South America has long provided ideal conditions for harmful algal blooms to form for millions of years.
The researchers say that taphonomic analysis reveals that toxins generated by HABs poisoned the whales and other ocean-going vertebrates, killing them fairly quickly[2]. Their carcasses then floated toward the coast where they were washed into a barrier-protected tidal flat by waves where they were protected from marine scavengers. The fact that there were no large terrestrial scavengers in South America at this time also allowed the bodies to remain unmolested as they were buried by sand.
Support for the conclusion that HABs were the cause of the deaths was provided by the discovery of orange splotches in the rock surrounding many of the skeletons that they thought were left by the chemical degradation of the algal mats. Examination of these splotches under a high-power microscope revealed tiny spheres similar to those found in dinoflagellates -- the plankton responsible for producing red tides.
Still, due to their degragation over millions of years it is not possible to definitively confirm that they came from a species associated with harmful algal blooms. As Pyenson noted, "It's a good candidate, but we can't exclude the possibility that these have a geological origin."
The results of the research were published today in the science journal "Proceedings of the Royal Society B"
1. about a kilometer (a little more than a half mile) from the current Pacific shoreline of the Pacific Ocean roughly 708 km (440 miles) or so north of the Chilean capital Santiago.
2. This is supported by the high percentage of the skeletons which were found belly-up which means they were already dead when they washed ashore rather than beaching themselves.
Further Reading:
Repeated mass strandings of Miocene marine mammals from Atacama Region of Chile point to sudden death at sea Abstract & Paper
Whale graveyard reveals most ancient mass strandings
Smithsonian scientists solve 'sudden death at sea' mystery
Ancient Whale Graveyard Discovered in Chile, Solves Mystery of Sudden Death at Sea
The Tiny Culprit Behind A Graveyard of Ancient Whales
Chile's stunning fossil whale graveyard explained
Whale graveyard shows mass stranding of species millions of years ago
Mystery of Atacama Desert whale graveyard solved
Killers Were Tiny, Victims Were Huge At Chile's Whale Graveyard
Chile's stunning fossil whale graveyard explained Short video
Excellent images from the site