Sharks Nearly Went Extinct 19 Million Years Ago From Mystery Event 75
An anonymous reader quotes a report from The New York Times: Researchers believe they've now pinpointed a previously unknown planetary-scale reset that occurred about 19 million years ago. This extinction event transpired in the world's oceans, and decimated shark populations. The boneless fishes still have not recovered from the damage, the team suggests in a paper published Thursday in Science. Scales cover the bodies -- and even the eyeballs -- of sharks. Known as "dermal denticles," these scales function like protective armor and their ridges also reduce drag as the animals swim, said Elizabeth C. Sibert, an oceanographer and paleontologist at Yale University. These scales are microscopic -- each one is only about the width of a human hair -- but sharks slough off about 100 denticles for each tooth they lose, making them common in the fossil record. This abundance makes them valuable to scientists seeking to understand the past, said Paul Harnik, a paleobiologist at Colgate University, not involved in the research. "It's a sheer numbers game."
In 2015, Dr. Sibert received a box of mud spanning about 40 million years of history. The reddish clay, extracted from two sediment cores that had been drilled deep into the Pacific Ocean seafloor, contained fish teeth, shark denticles and other marine microfossils. Using a microscope and a very fine paintbrush, Dr. Sibert picked through the two sediments and counted the number of fossils in samples separated in time by several hundred thousand years. About halfway through her data set, Dr. Sibert spotted an abrupt change in the fossil record. Nineteen million years ago, the ratio of shark denticles to fish teeth changed drastically: Samples older than that tended to contain roughly one denticle for every five fish teeth (a ratio of about 20 percent), but more recent samples had ratios closer to 1 percent. That meant that sharks suddenly became much less common, relative to fish, during an era known as the early Miocene, Dr. Sibert concluded. Dr. Sibert and her collaborators, in an earlier study using the same data set, had also found that sharks declined in abundance by roughly 90 percent about 19 million years ago. These declines in relative and absolute shark abundance suggest that something happened to shark populations about 19 million years ago, Dr. Sibert concluded.
But there was still the question of whether a true extinction occurred, she said. "We wanted to know if the sharks went extinct, or if they just became less prominent." To test the idea of an extinction, Dr. Sibert recruited Leah D. Rubin, a marine scientist then at the College of the Atlantic in Maine. Together, they developed a framework to identify distinct groups of denticles. The researchers settled on 19 denticle traits -- such as their shape and the orientation of their ridges. Dr. Sibert and Ms. Rubin sorted roughly 1,300 denticles into 88 groups. These groups don't correspond exactly to shark species, but seeing more groups is an indicator that a shark population is more diverse, the researchers proposed. Of the 88 denticle groups initially present before 19 million years ago, only nine persisted afterward. The reduction in shark diversity suggests that they experienced an extinction around that time, Dr. Sibert and Ms. Rubin concluded. In fact, this event was probably even more cataclysmic to sharks than the dinosaur-killing asteroid impact that occurred 66 million years ago, they said. "There were just a small fraction that survived into this post-extinction world," Dr. Sibert said. The researchers have no idea what caused this massive die-off. "There were no significant climatic changes in the early Miocene, and there's no evidence of an asteroid impact around that time," the report says.
In 2015, Dr. Sibert received a box of mud spanning about 40 million years of history. The reddish clay, extracted from two sediment cores that had been drilled deep into the Pacific Ocean seafloor, contained fish teeth, shark denticles and other marine microfossils. Using a microscope and a very fine paintbrush, Dr. Sibert picked through the two sediments and counted the number of fossils in samples separated in time by several hundred thousand years. About halfway through her data set, Dr. Sibert spotted an abrupt change in the fossil record. Nineteen million years ago, the ratio of shark denticles to fish teeth changed drastically: Samples older than that tended to contain roughly one denticle for every five fish teeth (a ratio of about 20 percent), but more recent samples had ratios closer to 1 percent. That meant that sharks suddenly became much less common, relative to fish, during an era known as the early Miocene, Dr. Sibert concluded. Dr. Sibert and her collaborators, in an earlier study using the same data set, had also found that sharks declined in abundance by roughly 90 percent about 19 million years ago. These declines in relative and absolute shark abundance suggest that something happened to shark populations about 19 million years ago, Dr. Sibert concluded.
But there was still the question of whether a true extinction occurred, she said. "We wanted to know if the sharks went extinct, or if they just became less prominent." To test the idea of an extinction, Dr. Sibert recruited Leah D. Rubin, a marine scientist then at the College of the Atlantic in Maine. Together, they developed a framework to identify distinct groups of denticles. The researchers settled on 19 denticle traits -- such as their shape and the orientation of their ridges. Dr. Sibert and Ms. Rubin sorted roughly 1,300 denticles into 88 groups. These groups don't correspond exactly to shark species, but seeing more groups is an indicator that a shark population is more diverse, the researchers proposed. Of the 88 denticle groups initially present before 19 million years ago, only nine persisted afterward. The reduction in shark diversity suggests that they experienced an extinction around that time, Dr. Sibert and Ms. Rubin concluded. In fact, this event was probably even more cataclysmic to sharks than the dinosaur-killing asteroid impact that occurred 66 million years ago, they said. "There were just a small fraction that survived into this post-extinction world," Dr. Sibert said. The researchers have no idea what caused this massive die-off. "There were no significant climatic changes in the early Miocene, and there's no evidence of an asteroid impact around that time," the report says.
Sharkdemic (Score:5, Funny)
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I'm not sure I want to watch that obvious SyFy movie. Nor am I *really* wanting anyone to tell SyFy about that movie idea. But someone (SyFy) should definitely make that movie.
Re: Sharkdemic (Score:2)
Shark std (Score:3)
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Not really. Evolutionarily speaking, viruses tend towards the harmless. The ones which damage their hosts' ability to reproduce wouldn't, themselves, be able to procreate beyond the immediate host, thus limiting their genetic spread.
It's possible, just highly unlikely.
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Nah. In the base article they mention that it's hard to get core samples from that time period, while the time periods around it are still relatively easy to spot. They didn't do the extrapolation on that point, but it makes me wonder if there wasn't some sort of cataclysmic upheaval of the oceans during that time. I wouldn't begin to speculate what that upheaval could have been, other than to say the sediment either was kept stirred up for a long period of time, or the waters moved so much during that t
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Giorgio A. Tsoukalos says (Score:2, Funny)
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Then what happened to all the creatures on land that didn't have a gazillion cubic gallons of water to absorb all that energy?
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Then what happened to all the creatures on land that didn't have a gazillion cubic gallons of water to absorb all that energy?
Not being slowed down by the water, they were able to dodge the quasars.
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Nah, clearly it was aliens [youtube.com]...
Menu Theory (Score:1)
Some other animal probably found them delicious relatively suddenly, and it took them a while to counter-adapt.
Re:Menu Theory (Score:5, Interesting)
Great white sharks will haul ass and not return to the same area for up to a year once orcas arrive on the scene.
https://www.smithsonianmag.com... [smithsonianmag.com]
Dolphins evolved about 50M years ago, and orcas (which are a type of dolphin) about 5M years ago.
If I had to guess, I'd say somewhere between those two periods there was probably a killer whale ancestor that found sharks delicious and may shark species were slow to adapt, getting wiped out, seeing as how the shark most people would consider the apex of apex predators is so keen to avoid orcas these days.
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seeing as how the shark most people would consider the apex of apex predators is so keen to avoid orcas these days.
Great white sharks are only considered the apex of apex predators because of that movie. Orcas, with their huge, wrinkly, mammal brain should frighten the shit out of anyone.
"fishes" (Score:1)
What the actual fuck.
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I can haz dictionary?
You're one of these idiots who attempts to "correct" people, but you didn't even look it up first? What the actual fuck?
Predators (Score:5, Insightful)
When a predator dies off isn't it usually because of a collapse in prey population and food source?
If not wouldn't there be a proportional rise, or spike, in whatever sharks were munching on then?
Or is the shark population's impact on the fish population negligible normally?
What I've read only talks about the fish teeth to shark denticles ratios but not the actual numbers.
Unless I've missed something? Anyone got access to the full paper?
Interesting article but it feels like there must be more to this than just the sharks.
Something Similar (Score:4, Interesting)
That time period might be long enough to coincide with geologic changes to the Earth’s crust, to the ocean’s salinity or temperature. It might overlap with the emergence of a species that developed the ability to digest shark denticles before that same species evolved onwards.
Your challenge about the population of apex predators being intrinsically linked to the population of their prey is even more likely. Maybe there is more background here that helps explain how the researchers were able to eliminate all the other possible explanations and conclude that this was a near-extinction event that impacted sharks and not other marine species
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Two words (Score:1)
Chuck Norris.
Shark Norris (Score:2)
How could you fsck that up ?-)
Four words (Score:1)
laser beam shark wars
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Just like dinosaurs. (Score:1)
alternatively (Score:5, Insightful)
"We wanted to know if the sharks went extinct, or if they just became less prominent."
or if they moved away from that one point in the ocean where the sample was taken.
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Re: alternatively (Score:2)
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What they need is not just another set of researchers looking at different things in the same data set. What they need is additional data sets.
They can't confirm anything by reworking the same data, all they can do is exclude specific types of statistical error.
3 words: Sharks with Lasers (Score:1)
According to a baseless theory I just made up, that's right around the time Sharks discovered lasers. If this massive mutuallly assured destruction event had not happened, they could come out of the water and grown legs.
I say it's either that or my alternative working theory is Sharknado dropped the sharks right in the middle of the desert :p
Heck, I almost went extinct last week... (Score:3)
Megalodon (Score:2)
Dolphins? (Score:1)
Sasquatch: Apex Predator (Score:1)
19 million years ago? Is that is when sasquatch emerged as the all-continent, all-habitat apex predator?
https://i1.wp.com/boingboing.n... [wp.com]
extrapolating from limited data (Score:2, Insightful)
If/when we get global samples of the same time period and span, then we can talk about a "shark extinction event". That one, two, or even five locations show a drop in shark apparent shark populations is something to be categorized as "interesting, needs more data", but means nothing. Globally, what else was happening? Locally, was there some other change to the environment to make it lass attractive to sharks?
Worth publishing the data to get others to add to it, but total fraud to attach any meaning to i
Comment removed (Score:4, Informative)
Re: extrapolating from limited data (Score:2)
That is right, but nothing in the second paragraph suggests that they had more mud samples to work with. The way I read it, they continued the research with the denticles from the initial mud sample.
Orcas (Score:2)
The first whales evolved 50 Million years ago. Orcas are only known from much later than this event. But the evolution of such large predators must have had such an effect on sharks. Since this is the only mystery decline of sharks it must have been that one.
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My theory is that it was caused by the evolution of large carnivorous whales.
Agreed. If it was a one-time event that reduced the population, if there was no major difference in the ecosystem the population would have rebounded. With marine mammals, you now had both a competitor for resources and in some cases, a new predator that was eating you.
What gives? (Score:2)
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I'm tired of hearing that
OK, fine, are you tired enough to finally listen? You were wrong decades ago, and you're too stupid to figure that out, even given nearly unlimited time and repeatedly being told about it?
Rate? (Score:2)
Re:Rate? (Score:5, Informative)
The teeth are from all kinds of fish. The denticles only from sharks.
That is how they measure the ratio of fish vs sharks.
Re: Rate? (Score:2)
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And so (Score:2)
The researchers have no idea what caused this massive die-off.
Way Bigger Jaws
Sample size (Score:2)
Dr. Sibert received a box of mud
I certainly hope yhese convlusions were reached based on a larger sample size than one.
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For this statistical transgression, his name is Mudd.
Evolution? (Score:2)
The laser beams were (Score:1)
...installed in the wrong direction.
Microscopic? (Score:2)
These scales are microscopic -- each one is only about the width of a human hair
Human hair is visible to the naked eye, it is not microscopic.
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These scales are microscopic -- each one is only about the width of a human hair
Human hair is visible to the naked eye, it is not microscopic.
A short object, not long like a hair, that is the width of human hair is microscopic.
Width of a human hair" means 75 microns, though some hairs are somewhat thicker than this, others are less than half. Human visual resolution of a dot-like object is about 100 microns. You can see a hair that is thinner than this because it is straight and long, and crosses many retinal cell detection zones, and the retina and brain cells can extract the path from the data.
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You're a fucking idiot. An object visible to the naked eye is not microscopic.
Martin Brody (Score:2)
He is the most likely suspect . . .
That's not what "decimate" means (Score:2)
Sharknado! (Score:2)
Extiniction? (Score:2)