Springtime collision

I've written here before about the rather sobering topic of mass extinctions, and from what reading I've done on the topic, it always leaves me thinking about how fragile Earth's ecosystems are.  Most of the biggest extinctions were not due to a single cause, though; for example, the Ordovician-Silurian extinction of about 445 million years ago seems to have been touched off by plate tectonics -- the massive southern continent of Gondwana meandered across the south pole, leading to ice cap formation, massive glaciation, and a drop in sea level.  However, there followed a huge drop in atmospheric oxygen and spike in sulfur, leading to worldwide oceanic anoxia.  The result: an estimate 60% mortality rate in species all over the Earth.

Anoxia is also thought to have played a role in the largest mass extinction ever, the Permian-Triassic extinction of 252 million years ago.  This one, however, seems to have begun with a catastrophic volcanic eruption that boosted the carbon dioxide in the atmosphere, and thus the temperature.  Temperature is inversely related to oxygen solubility, so as the oceans warmed, what oxygen was left in the air didn't dissolve as well, and nearly everything in the oceans died (a mortality rate estimated at an almost unimaginable 95%).  This caused an explosive growth in anaerobic bacteria, pumping both carbon dioxide and methane into the atmosphere.  The average temperature skyrocketed by as much as ten degrees Celsius.

Even the smaller extinctions seldom come from one cause.  I wrote recently about the Eocene-Oligocene extinction, which wiped out a good many of Africa's mammal species (our ancestors survived, fortunately for us), and was apparently an evil confluence of three unrelated events -- rapid cooling of the climate after the Paleocene-Eocene Thermal Maximum, a massive meteorite collision near what is now Chesapeake Bay, and explosive volcanism in Ethiopia.

The exception to the rule seems to be the most famous extinction of all, the Cretaceous-Tertiary extinction of 66 million years ago.  The one that ended the hegemony of the dinosaurs.  I always find it wryly amusing when the dinosaurs are described as some kind of evolutionary dead-end, as if their failure to survive to today is indicative that they were inferior or maladapted.  In fact, the dinosaurs as such were the dominant group of terrestrial animals for almost two hundred million years -- from the late Permian to the end of the Cretaceous -- and that's not counting birds, which are (frankly) dinosaurs, too.  That means if you consider the earliest modern humans to have lived in Africa on the order of three hundred thousand years ago, the dinosaurs kind of ran the planet for over six hundred times longer than we've even existed.

And in the blink of an eye, everything changed.  Far from being an evolutionary cul-de-sac, the dinosaurs were doing just fine, when a meteor ten kilometers in diameter slammed into the Earth near what is now the Yucatán Peninsula of Mexico.  And now scientists have been able to pinpoint not only where the collision happened, but what time of year -- the middle of the Northern Hemisphere's spring.

The Chicxulub Impact, as visualized by artist Donald E. Davis [image is in the Public Domain courtesy of NASA]

Paleontologists working in North Dakota have found a rich fossil site that was created on that fateful day.  Pre-collision, the area was a wet lowland forest with a shallow river.  The slow-moving water was the home of paddlefish and sturgeon, swimming slowly and nosing around in the mud for food.  Then, three thousand kilometers away, the meteor struck.  The shock wave ejected a sheet of superheated steam and molten rock skyward; the impact, which occurred in what was (and still is) a shallow marine region, generated a tsunami the likes of which I can't even imagine.  The southern part of North America got flash-fried by the heat generated by the strike; only a few minutes later, it was followed by a wall of water the height of a skyscraper that swept across the land at an estimated five hundred kilometers an hour.

The first thing the fish would have noticed, though, is a rain of tiny globs of molten glass that sizzled as they hit the water and settled out, coating the riverbed and clogging their gills.  Then the tsunami hit, burying the site under thick layers of sediment.  By the time things calmed down, most of the living things in North America were dead, their fossils left behind as a near-instantaneous photograph of one of the worst days the Earth has ever seen.

It's the quickness of the event that allowed scientists to figure out when it happened.  Paddlefish bones form growth layers -- a little like the rings inside a tree trunk -- and all of the paddlefish fossils from the site show an increasing rate of growth, but not yet at its annual peak (which occurs in the warmest parts of summer).  The Chicxulub meteorite seems to have struck the Earth in April or May.

This may be another reason why the Northern Hemisphere flora and fauna took a much bigger hit than the ones in the Southern Hemisphere.  The initial explanation was that the meteor struck the Earth at an angle, on with a trajectory on the order of forty-five degrees south of vertical, so the shower of molten debris mostly got blasted northward.  (This may well be true; the current research doesn't contradict that assessment.)  But if the strike occurred in the Northern Hemisphere's spring, when plants are leafing out and flowering, and animals increasing in activity, it would have been catastrophic.  The ones in the Southern Hemisphere, heading into fall and winter, would have been in the process of powering down and moving toward dormancy and hibernation, and may have been more insulated from the effects.

Besides the obvious fascination of an event so cataclysmic, it's just stupendous that we can analyze the evidence so finely that we can determine what time of year it occurred, 66 million years later.  It also highlights how suddenly things can change.  The dinosaurs had been around for two hundred million years, surviving not only the colossal Permian-Triassic extinction but the smaller (but still huge) end-Triassic extinction, that took out thirty percent of the species on Earth.  In one particular April of 66 million years ago, a quick look around would have led you to believe that everything was fine, and that the dinosaurs and other Mesozoic critters weren't going anywhere.

A day later, the entire face of the Earth had changed forever.

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Meet Wonderchicken

Since Jurassic Park, it hasn't been news to most people that birds are dinosaurs.  The evidence from skeletal analysis is unequivocal; not only is your average little garden sparrow a dinosaur, it's close cousin to one of the most famous prehistoric animals, the fearful Velociraptor.  (Which apparently was a pack hunter, but probably wasn't smart enough to figure out how to unlatch a freezer door, so take what you see in the movies with a grain of salt or two.)

The mystery is why the ancestors of modern birds survived, and all of the other dinosaur lineages died out.  The old saw of "the dinosaurs were dying out anyhow, and the meteorite impact finished 'em off" is almost certainly untrue; the dinosaurs were apparently doing just fine when Chicxulub hit, flash-frying anything nearby and causing global havoc (and nearly simultaneously the colossal Deccan Traps volcanic eruptions occurred -- geologists are still debating whether those two events are causally linked).

But whatever the cause(s), the dinosaurs were clearly doing well, then whammy.  And, for what it's worth, they'd been pretty much in charge of the world for the entire Mesozoic Era, a time span of 180 million years (and to put that in perspective, that's over a hundred times longer than Homo sapiens has been in ascendancy).  It's probable that the reason most of the best-known species of dinosaurs became extinct is that when conditions suddenly become dire, the two groups to suffer most are the large species and the extreme specialists, both of whom are intolerant to a rapidly changing environment.  But hard evidence of this, in the form of fossils from right around the time of the end-Cretaceous Extinction, have been few and far between.

This week a paper in Nature added a new piece to the puzzle -- a fossil bird from 66.7 million years ago, only 700,000 years before Chicxulub et al. said finis to the Age of the Dinosaurs.  So here we have in hand a species that probably made it through the bottleneck -- because it looks like what may well be the common ancestor between galliform birds (chickens and turkeys) and waterfowl.

In "Late Cretaceous Neornithine from Europe Illuminates the Origins of Crown Birds," by Daniel Field, Juan Benito, and Albert Chen (of Cambridge University), John Jagt (of Natuurhistorisch Museum Maastricht in the Netherlands), and Daniel Ksepka (of the Bruce Museum of Greenwich, Connecticut), we read about read about a fascinating find that the researchers have dubbed "Wonderchicken:"

Our understanding of the earliest stages of crown bird evolution is hindered by an exceedingly sparse avian fossil record from the Mesozoic era.  The most ancient phylogenetic divergences among crown birds are known to have occurred in the Cretaceous period, but stem-lineage representatives of the deepest subclades of crown birds—Palaeognathae (ostriches and kin), Galloanserae (landfowl and waterfowl) and Neoaves (all other extant birds)—are unknown from the Mesozoic era.  As a result, key questions related to the ecology, biogeography, and divergence times of ancestral crown birds remain unanswered.  Here we report a new Mesozoic fossil that occupies a position close to the last common ancestor of Galloanserae and fills a key phylogenetic gap in the early evolutionary history of crown birds.  Asteriornis maastrichtensis, gen. et sp. nov., from the Maastrichtian age of Belgium (66.8–66.7 million years ago), is represented by a nearly complete, three-dimensionally preserved skull and associated postcranial elements.  The fossil represents one of the only well-supported crown birds from the Mesozoic era, and is the first Mesozoic crown bird with well-represented cranial remains.  Asteriornis maastrichtensis exhibits a previously undocumented combination of galliform (landfowl)-like and anseriform (waterfowl)-like features, and its presence alongside a previously reported Ichthyornis-like taxon from the same locality provides direct evidence of the co-occurrence of crown birds and avialan stem birds.  Its occurrence in the Northern Hemisphere challenges biogeographical hypotheses of a Gondwanan origin of crown birds, and its relatively small size and possible littoral ecology may corroborate proposed ecological filters that influenced the persistence of crown birds through the end-Cretaceous mass extinction.

This fossil is pretty spectacular -- and unique.  "It shows a never previously seen mashup of ducklike and chickenlike features," said study lead author Daniel Field, a vertebrate paleontologist at the University of Cambridge.  "It’s like a turducken."

This pushes forward the date estimated for the last common ancestor of all modern birds, previously estimated by molecular clock data as between 139 and 89 million years ago.  Asteriornis is a very close ally to the ancestor of two large bird groups, so it could be that true birds evolved much closer to the end-Cretaceous Extinction than we'd previously thought.

So I'm sure you're wondering what Wonderchicken looked like.  Here's an artist's reconstruction (art by Phillip Krzeminski):

Recognizably a bird, isn't it?  Not some scary toothy flying dinosaur like Archaeopteryx.  Poor thing, little did it know that hard times were coming, although maybe knowing its descendants would be some of the survivors would have cheered it up.

And its relevance was obvious the moment the team saw the results of the computerized tomography of the skull.  "The timeline was: See the skull, scream ‘Holy shit,’ give my Ph.D. student a high five, and then start calling it the Wonderchicken," Field said, in an interview with Science News.

Wonderchicken was about the size of a modern quail, further supporting the conjecture that small size was a factor in surviving the bottleneck.

So that's another piece in the evolutionary puzzle, and something to think about next time you fill the birdfeeders for the local chickadees.  Modern biodiversity has been mostly shaped by evolution, but random and unpredictable natural disasters played their own role in determining who the winners and losers would be.  And here we have hard evidence of one of the winners -- an unprepossessing bird from right before one of the biggest catastrophes the Earth has ever seen.

Wonderchicken, indeed.

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This week's Skeptophilia book recommendation of the week is a classic -- Martin Gardner's wonderful Did Adam and Eve Have Navels?

Gardner was a polymath of stupendous proportions, a mathematician, skeptic, and long-time writer of Scientific American's monthly feature "Mathematical Games."  He gained a wonderful reputation not only as a puzzle-maker but as a debunker of pseudoscience, and in this week's book he takes on some deserving targets -- numerology, UFOs, "alternative medicine," reflexology, and a host of others.

Gardner's prose is light, lucid, and often funny, but he skewers charlatans with the sharpness of a rapier.  His book is a must-read for anyone who wants to work toward a cure for gullibility -- a cure that is desperately needed these days.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

Life finds a way

I've dealt more than once here at Skeptophilia with the repeated mass extinctions the Earth has undergone.  Part of this is that I have an admitted fascination with things that are big and powerful and can kill you.  These include:

• tornadoes and hurricanes
• lightning
• earthquakes
• volcanoes
• death asteroids from outer space

The latter is thought to have been the prime mover of the Cretaceous Extinction, which occurred 66 million years ago and killed an estimated 75% of the species on Earth, including all of the large dinosaurs (the exception being the lineage that led to modern birds).  Here's a cool, if terrifying, simulation of what it'd be like if the Earth got hit by an asteroid five hundred kilometers in diameter (the Chicxulub Meteorite, which caused the extinction, is estimated to be about a tenth that diameter, so you can scale down your picture of that event accordingly):

But dwelling on that stuff is a little morbid, even if it's kind of awe-inspiring.  So today, I'd like to look at some recent research that looks at how life recovered after the cataclysm -- discoveries that suggest the encouraging idea that even with a catastrophe, life can bounce back amazingly quickly.

A few years ago, Ian Miller and Tyler Lyson of the Denver Museum of Nature and Science were involved in a fossil dig in Corral Bluffs, Colorado, and made a rather astonishing discovery.  Initially the area seemed to be rather fossil-poor, but it had a great many concretions (roughly spherical blobs of cemented sediment).  When Miller and Lyson split one of these open, they found it was full of skeletal remains.

It turns out Corral Bluffs represent sedimentary layers of rock deposited immediately after the collision, so it provides an incredibly detailed record of the years following.  Large animals and flowering plants (especially trees) were hit the hardest by the extinction; despite the prevailing wisdom that "dinosaurs died and mammals didn't," the more accurate statement is "big species were much more likely to die than little ones."  The bottleneck, in fact, seems to have taken out all the mammals larger than your average rat.  (Miller and Lyson found no evidence of mammals larger than six hundred grams that survived the extinction.)  Miller, who is a paleobotanist, concentrated not on the animal remains but the plants -- especially the 37,000 pollen grains he found fossilized in the sediment layers.  And from this, a picture began to emerge of what things were like in the years following the collision, which was described this week in a fascinating paper in Science.

The largest group of plants to come through the bottleneck were ferns, which thrive in disturbed areas and have spores that are pretty damage-resistant.  Unfortunately for the animals, fern leaves and roots are rather low in nutrients, so for a while, body sizes remained small because there simply wasn't enough food around to support big, or even medium-sized, herbivores.  But within a few thousand years -- a flash, evolutionarily speaking -- Fern World was replaced by Palm World, as proto-monocots (the group that contains not only palms, but grasses, lilies, orchids, irises, and a variety of other familiar plant families) evolved to be more robust.  Palms have oily fruit that are high in sugar, and there's a commensurate jump in mammalian body size, with species showing up that weighed five kilograms.

Palms were superseded by the ancestors of today's walnuts and hickories a hundred or so thousand years after that, and in "Pecan Pie World" (as Miller and Lyson call this era), and the higher nutritional quality of those seeds fueled another jump in body size, with the largest ones reaching thirty kilograms (the size of a large dog).  And after seven hundred thousand years, legumes diversified, and the high protein content of these species triggered another growth spurt, topping out at fifty kilograms -- a hundred times larger than the survivors of the collision, in less than a million years.

Nota bene: the growth in size wasn't done yet.  The Oligocene Epoch, from 34 to 23 million years ago, saw the largest land mammals that have ever existed, including the enormous Baluchitherium, a behemoth that could have converted an African elephant into an African elephant pancake:

[Image licensed under the Creative Commons Waqas-anees2014, Baluchitherium, The Largest Land mammal at Pakistan Museum of Natural History (PMNH), CC BY-SA 3.0]

The Miller and Lyson study offers us a message that is simultaneously reassuring and terrifying.  First, the human-caused "Sixth Extinction" that we are almost certainly undergoing as we speak is not going to eliminate life on Earth, and the species that survive will quickly spring back and diversify once we stop doing whatever we can to make the planet uninhabitable.  But the cautionary tale is that no matter what, it won't be what we had.  The diversity of flora and fauna that existed before the Chicxulub Collision was gone forever, and even though "life found a way" (to borrow a phrase from Jurassic Park), what evolved afterward was dramatically different than what was lost.  And, to put not too fine a point on it, the years immediately following the bottleneck were pretty freakin' horrible for all concerned, with an entire planet laid waste, and the animals that weren't directly killed by the impact itself largely facing habitat loss and rampant starvation.

So we shouldn't be so quick to adopt the Pollyanna-ish "it'll all be fine, nature is resilient" attitude toward our current fossil-fuel-crazy, pollution-blind willfully ignorant behavior.  If anything, we should recognize how fragile it all is -- and how, if we push too hard, we're likely to see a collapse of catastrophic proportions.  While we can pretty much count on evolution eventually producing a whole new set of what Darwin called "endless forms most beautiful and most wonderful," there's more than a passing chance that we won't be around to see them.

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In keeping with Monday's post, this week's Skeptophilia book recommendation is about one of the most enigmatic figures in mathematics; the Indian prodigy Srinivasa Ramanujan.  Ramanujan was remarkable not only for his adeptness in handling numbers, but for his insight; one of his most famous moments was the discovery of "taxicab numbers" (I'll leave you to read the book to find out why they're called that), which are numbers that are expressible as the sum of two cubes, two different ways.

For example, 1,729 is the sum of 1 cubed and 12 cubed; it's also the sum of 9 cubed and 10 cubed.

What's fascinating about Ramanujan is that when he discovered this, it just leapt out at him.  He looked at 1,729 and immediately recognized that it had this odd property.  When he shared it with a friend, he was kind of amazed that the friend didn't jump to the same realization.

"How did you know that?" the friend asked.

Ramanujan shrugged.  "It was obvious."

The Man Who Knew Infinity by Robert Kanigel is the story of Ramanujan, whose life ended from tuberculosis at the young age of 32.  It's a brilliant, intriguing, and deeply perplexing book, looking at the mind of a savant -- someone who is so much better than most of us at a particular subject that it's hard even to conceive.  But Kanigel doesn't just hold up Ramanujan as some kind of odd specimen; he looks at the human side of a man whose phenomenal abilities put him in a class by himself.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

Titans of the ocean

As far as scary critters go, you'd have to look hard to find one scarier than the elasmosaurs.

If you've never seen an artist's reconstruction of one of these beasts, picture something like the body of a sea turtle, with an incredibly long neck and snake-like head, with lots of big, nasty, pointy teeth.  The largest ones reached a length of twelve meters, and a weight of several tons.  The conventional wisdom is that they "mostly ate crustaceans and mollusks," but my feeling is that if they encountered a swimmer, the result would be something like what happened in the movie Jaws, only worse.

Artist's reconstruction of Thalassomedon haningtoni, a late Cretaceous elasmosaur [Image licensed under the Creative Commons DiBgd, Thalassomedon haningtoni, CC BY-SA 4.0]

Fortunately for us, they are one of the groups that ran afoul of the Chicxulub Meteorite Impact 66 million years ago, and they all became extinct, unless you believe in the Loch Ness Monster, which would definitely be an elasmosaur if it actually existed.

This comes up because last week, paleontologists announced that they have unearthed a nearly-complete fossil of the largest-known elasmosaur, Aristonectes, which when alive would have been thirteen meters long and weighed twelve tons.  The fossil was found on Seymour Island in 1989, but was only excavated now because Seymour Island is at the tip of the Antarctic Peninsula, and is windswept, cold, hostile, and hard to get to even during the brief Antarctic summer.  The research team, led by José O’Gorman, a paleontologist with the National Scientific and Technical Research Council of Argentina (CONICET) who is based at the Museum of La Plata near Buenos Aires, has finished the excavation and submitted their results to the journal Cretaceous Research.

What to me is most fascinating about this specimen -- besides its sheer size, which is eye-opening enough -- is that it dates to only thirty thousand years before the K-T Extinction, which (palenontologically speaking) is barely any time at all.  So these big guys were thriving (and diversifying) right up to the moment the big crash occurred -- further evidence that the meteorite was the trigger to the entire extinction event.

O'Gorman says that the work to recover the specimen was grueling.  It began in 2012, proceeding at a snail's pace because the site was only accessible a couple of weeks a year, in late January and early February, and sometimes not even then if there was an unexpected storm. "The weather is one of the problems," O'Gorman said.  "The weather controls all.  Maybe one day you can work, and the next day you cannot because you have a snowstorm."

But their painstaking labor has finally paid off, and given us a picture of a truly awesome critter who was swimming around the oceans right on the verge of one of the "Big Five" extinction events.  Like I said, as a swimmer and scuba diver, I'm just as happy they're not around any more, but getting a glimpse of one of the largest aquatic predators the Earth has ever produced is enough to leave me in awe.
 
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This week's Skeptophilia book recommendation is a little on the dark side; Jared Diamond's riveting book Collapse: How Societies Choose to Fail or Succeed.  Starting with societies that sowed the seeds of their own destruction -- such as the Easter Islanders, whose denuding of the landscape led to island-wide ecological collapse -- he focuses the lens on the United States and western Europe, whose rampant resource use, apparent disregard for curbing pollution, and choice of short-term expediency over long-term wisdom seem to be pushing us in the direction of disaster.

It's not a cheerful book, but it's a very necessary one, and is even more pertinent now than when it was written in 2005.  Diamond highlights the problems we face, and warns of that threshold we're approaching toward catastrophe -- a threshold that is so subtle that we may well not notice it until it's too late to reverse course.

[If you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

Double whammy

Having a rather morbid fascination with things that are big and scary and dangerous and can kill you, I've dealt more than once with topics like mass extinctions and asteroid collisions and supervolcanoes.  So naturally, when there was a piece of recent research on all three at the same time, I felt obliged to write a post about it.

The paper, published last week in Science, was written by a team of scientists from the University of California - Berkeley (Courtney J. Sprain, Paul R. Renne, Loÿc Vanderkluysen, Kanchan Pande, Stephen Self, and Tushar Mittal), is called "The Eruptive Tempo of Deccan Volcanism in Relation to the Cretaceous-Paleogene Boundary."  In it, they examine one of the biggest volcanic eruptions in Earth's history -- the Deccan Traps -- which seem to have occurred right around the time of the Cretaceous Extinction, 66 million years ago.

The Western Ghats, part of the Deccan Traps lava flow [Image licensed under the Creative Commons Nicholas (Nichalp), Western-Ghats-Matheran, CC BY-SA 2.5]

This certainly isn't a coincidence, and it's been thought for a while that the eruption, which occurred in what is now India and released an estimated one million cubic kilometers of lava, were at least contributory to the mass extinction that occurred at the end of the Cretaceous Period.  Such an unimaginably huge eruption would have burned everything in its path, converting any organic matter that got in the way into ash and carbon dioxide -- causing a spike in temperature that certainly would have put a huge strain on ecosystems to compensate.  The actual blow (literally) that marked the end of the Cretaceous Period, though, was an enormous meteorite collision, the Chicxulub Impact, near the Yucatan Peninsula on the other side of the planet.

Almost precisely on the other side, in fact.  This got Sprain et al. wondering if the two might be connected, especially since geologists still don't know what causes trap-type eruptions (there are two other trap eruptions known, the Emeishan Traps in China and the unimaginably huge Siberian Traps that are likely to be the cause of the largest mass extinction known, the Permian-Triassic Extinction).  Whatever the cause, it apparently happens without a great deal of warning, which is scarier than hell.  The crust of the Earth fissures, and phenomenal quantities of lava come pouring out, causing serious issues for anyone or anything living nearby.  But the observation that the Chicxulub Impact and the Deccan Traps are not only close to simultaneous but are almost exactly antipodal made scientists wonder if that wasn't a coincidence.

Apparently, the thought is this.  When the Chicxulub Impact occurred, it sent huge shock waves through the Earth, which propagated both through the mantle and along the crust.  When those waves had traveled all the way around (or through) the Earth, they converged on a single point, almost like a magnifying glass bringing rays of sunlight focusing on one spot.  This reinforced the waves, ringing the Earth like a bell, and the crust destabilized...

... cracking open and creating one of the largest volcanic eruptions ever.

So the whole thing becomes a double whammy, and not because of an unfortunate accident.  It seems likely that one event caused the other, and also explains why species that lived in what is now Asia were affected just as much by the extinction as ones that were near the collision itself.  Seems kind of unfair, doesn't it?  The meteorite collides with the Earth, causing massive devastation in the Western Hemisphere, and the critters in the Eastern Hemisphere only had a few minutes to gloat before a massive earthquake launched an event that did them in, too.

"Both the impact and Deccan volcanism can produce similar environmental effects, but these are occurring on vastly differing timescales," study co-author Courtney Sprain said.  "Therefore, to understand how each agent contributed to the extinction event, assessing timing is key."

There you have it.  Yet another reason why we wouldn't want the Earth to get hit by a huge asteroid, if you needed another one.  Kind of dwarfs the earthquakes and volcanoes we've had recently, doesn't it?  Also makes me realize how fragile the biosphere is, and that a sudden and unforeseen event can trigger enormous destruction -- one a bolt from the sky, the other from the deepest regions of the Earth's mantle.

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This week's Skeptophilia book recommendation is a tour-de-force for anyone who is interested in biology -- Richard Dawkins's The Ancestor's Tale.  Dawkins uses the metaphoric framework of The Canterbury Tales to take a walk back into the past, where various travelers meet up along the way and tell their stories.  He starts with humans -- although takes great pains to emphasize that this is an arbitrary and anthropocentric choice -- and shows how other lineages meet up with ours.  First the great apes, then the monkeys, then gibbons, then lemurs, then various other mammals -- and on and on back until we reach LUCA, the "last universal common ancestor" to all life on Earth.

Dawkins's signature lucid, conversational style makes this anything but a dry read, but you will come away with a far deeper understanding of the interrelationships of our fellow Earthlings, and a greater appreciation for how powerful the evolutionary model actually is.  If I had to recommend one and only one book on the subject of biology for any science-minded person to read, The Ancestor's Tale would be it.

[If you purchase the book from Amazon using the image/link below, part of the proceeds goes to supporting Skeptophilia!]

Myths, mammals, and extinctions

It's interesting how the scientific version of urban legends can be incorporated into people's knowledge of how things work, and become so entwined that most folks don't even know which bits are true and which aren't.

Stephen Jay Gould riffed on this theme in his essay "The Case of the Creeping Fox Terrier Clone," which appeared first in Natural History and was later published in his essay collection Bully for Brontosaurus.  He looks at the claim that an early horse species, Hyracotherium, was "the size of a fox terrier" -- something that Gould found quoted in dozens of books on prehistoric animals (and which has therefore been used as a gauge of the animal's size in countless classrooms).  It turns out that it originated with a paleontologist, O. C. Marsh, who said Hyracotherium was the "size of a fox" -- a significant underestimate, as both foxes and fox terriers top out at around twenty pounds, and Hyracotherium weighed in at something closer to sixty.  But the analogy stuck, and people continued to pass it along without checking its veracity -- giving us the impression of tiny dog-sized horses, lo unto this very day.

Another example of this, from the same field, is that mammals were small, few in number, and low in biodiversity until along came a meteorite that for some reason selectively killed all the dinosaurs, leaving the mammals to throw a great big party and evolve like mad into the species we have around today.  This is incorrect on a variety of levels:

1. The K-T (Cretaceous/Tertiary) Extinction of 66 million years ago seems to have been caused by a double whammy -- the aforementioned meteorite, which left the Chicxulub Crater in what is now the Gulf of Mexico, and the formation of the Deccan Traps, a lava field from a colossal supervolcano eruption, all the way around the Earth in what is now India.
2. Dinosaur biodiversity had been decreasing for some time before the K-T Extinction, and in fact by some estimates was already down 40% from its peak during the mid-Cretaceous.
3. ...however...  All the dinosaurs didn't go extinct 66 million years ago, and I'm not talking about Nessie, Ogopogo, and Mokélé-Mbembe.  We still have dinosaurs around, we just call 'em birds.  The evidence is now incontrovertible.  Think about that next time you're putting out sunflower seeds for the chickadees.
4. The extinction hit pretty much every taxon that existed at the time.  The hardest-hit were large carnivores -- a vulnerable spot in the food chain at the best of times -- but no one escaped unscathed.  In fact, one group that got wiped out completely were the ammonites, a cephalopod mollusk that had thrived for 350 million years before getting clobbered during the K-T Extinction.
5. Most pertinent to this post, the mammals weren't just skulking around waiting for their opportunity; they'd been thriving alongside dinosaurs since the Triassic Period, 154 million years earlier.  This was the topic of a paper released a couple of months ago in Biology Letters by Tiago Bosisio Quental of the University of São Paulo and Mathias Pires of the University of Campinas.

What Quental and Pires did is a thorough survey of mammalian fossils, analyzing biodiversity as a function of time in three of the four big lineages of mammals -- Eutherians (most of the mammals you're familiar with), Metatherians (marsupials), and Multituberculates (an odd group of rodent-like mammals that were only distantly related to the rest of Class Mammalia, and which were one of the most common groups of mammals for almost two hundred million years).  They didn't include the fourth lineage -- the Monotremes, or egg-laying mammals -- only because they are extremely rare in the fossil record.

A late Cretaceous multituberculate, Catopsbaatar [Image licensed under the Creative Commons, Artwork by Bogusław Waksmundzki. Article by Zofia Kielan-Jaworowska and Jørn H. Hurum, Catopsbaatar, CC BY 2.0]

What they found -- predictably -- is that the dynamics of the extinction, and the years following it, is far more complex than it's usually represented.  "All these mass extinction episodes are heterogeneous," study co-author Pires said.  "They occurred for different reasons and unfolded in different ways.  Their impact on life forms was not absolute but relative.  Some groups suffered more, others less.  Some disappeared, while others took advantage of the new environmental conditions after the catastrophe to diversify rapidly."

Even within groups, the extinction didn't have uniform effects.  "Extinctions were concentrated among the specialized carnivorous metatherians and insectivorous eutherians," Pires said, "whereas more generalized eutherians and multituberculates survived and maintained higher diversity."

He added, "This means that studies of macroevolutionary phenomena focusing on broad taxonomic groups may miss a much richer macroevolutionary history, which can be perceived only at finer taxonomic scales."

Which can more generally be summed up as "the simple explanation is usually wrong."  It'd be nice if things weren't so complex, especially for we non-scientists.  But like Gould's fox-terrier-horse, many of these oversimplifications are flat-out incorrect -- and the truth is so much more interesting.

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This week's Skeptophilia book recommendation is one of personal significance to me -- Michael Pollan's latest book, How to Change Your Mind.  Pollan's phenomenal writing in tours de force like The Omnivore's Dilemma and The Botany of Desire shines through here, where he takes on a controversial topic -- the use of psychedelic drugs to treat depression and anxiety.

Hallucinogens like DMT, LSD, ketamine, and psilocybin have long been classified as schedule-1 drugs -- chemicals which are off limits even for research except by a rigorous and time-consuming approval process that seldom results in a thumbs-up.  As a result, most researchers in mood disorders haven't even considered them, looking instead at more conventional antidepressants and anxiolytics.  It's only recently that there's been renewed interest, when it was found that one administration of drugs like ketamine, under controlled conditions, was enough to alleviate intractable depression, not just for hours or days but for months.

Pollan looks at the subject from all angles -- the history of psychedelics and why they've been taboo for so long, the psychopharmacology of the substances themselves, and the people whose lives have been changed by them.  It's a fascinating read -- and I hope it generates a sea change in our attitudes toward chemicals that could help literally millions of people deal with disorders that can rob their lives of pleasure, satisfaction, and motivation.

[If you purchase the book from Amazon using the image/link below, part of the proceeds goes to supporting Skeptophilia!]

Science shorts

After the last three days' depressing posts, I thought it was once again time to retreat to my happy place, which is: cool new scientific research.  So, for your reading entertainment, here are some early-summer shorts.

[Image licensed under the Creative Commons marcore! from Hong Kong, China, Board shorts 4, CC BY 2.0]

No, not those kind of shorts.  The scientific variety.

First, we have some research that appeared last week in the Journal of Applied Research in Memory and Cognition, done by Julia Soares and Benjamin Storm of the University of California.  In their paper, entitled, "Forget in a Flash: A Further Investigation of the Photo-Taking Impairment Effect," what Soares and Storm found that for reasons still unknown, taking a photo of something impairs your ability to remember it -- even if you know that you won't have access to the photo later.

The authors write:

A photo-taking-impairment effect has been observed such that participants are less likely to remember objects they photograph than objects they only observe.  According to the offloading hypothesis, taking photos allows people to offload organic memory onto the camera's prosthetic memory, which they can rely upon to “remember” for them.  We tested this hypothesis by manipulating whether participants perceived photo-taking as capable of serving as a form of offloading.  In [our] experiments, participants exhibited a significant photo-taking-impairment effect even though they did not expect to have access to the photos.  In fact, the effect was just as large as when participants believed they would have access to the photos.  These results suggest that offloading may not be the sole, or even primary, mechanism for the photo-taking-impairment effect.

The authors were interviewed by Alex Fradera for the Research Digest of the British Psychological Society, and there's a possible explanation for the phenomenon, although it's still speculative.  Fradera writes:

Soares and Storm have a speculative second interpretation.  They suggest that the effort involved in taking a photo – getting the framing right, ensuring the lens is in focus – leads to the sense that you’ve done a good job of encoding the object itself, even though you have been focusing more on peripheral features.  So you’re not mentally slacking-off because you think the camera has it covered – but because you think you already have.  It may be relevant that people who take photographs at events report afterwards feeling more immersed in the experience, which would tally more with this explanation than the disengagement-due-to-fiddling idea.  In any case this is further evidence that those of us who approach exciting life events through the lenses of our electronic devices may be distancing ourselves from fuller participation.

From the Department of Geophysics at the University of Texas comes a study of the most famous (although not, by a long shot, the largest) mass extinction event -- the Cretaceous-Tertiary Extinction of 65 million years ago, which took out the dinosaurs, with the exception of the ancestors of today's birds.  The accepted explanation of the event is a collision by a massive meteorite near what is now the Yucatán Peninsula, forming the Chicxulub Crater.

A long-unanswered question about mass extinctions such as this one is how fast life rebounded.  The problem is that the difference between a thousand, ten thousand, and a hundred thousand years in the geological record isn't that great, so the error rate for any estimates were bound to be high.  But now, geophysicists Chris Lowery, Gail Christeson, Sean Gulick, and Cornelia Rasmussen, working with Timothy Bralower, a micropaleontologist at Pennsylvania State University, have found evidence that narrows that window down -- and surprisingly, shows that life recovered pretty quickly.

The key was finding a sediment core that contained 76 centimeters of brown limestone that came from the years immediately following the impact.  It contained debris from the event, including crystals of "shocked quartz" (quartz crystals showing signs of sudden, extreme temperatures and pressures).  And what the researchers found was that a little as a few thousand years, the ecosystem was beginning to rebound.

"You can see layering in this core, while in others, they’re generally mixed, meaning that the record of fossils and materials is all churned up, and you can’t resolve tiny time intervals," Bralower said.  "We have a fossil record here where we’re able to resolve daily, weekly, monthly, yearly changes."

Speaking of catastrophes, a fascinating piece of research from Stanford University anthropologists Tian Chen Zeng, Alan Aw, and Marcus Feldman gives us a possible explanation for a peculiar calamity that the human race experienced only seven thousand years ago.  By analyzing the genetic diversity among human Y-chromosomal DNA (inherited only father-to-son) and comparing it to the diversity in mitochondrial DNA (inherited only mother-to-child), they found something decidedly odd; the data suggested a serious genetic bottleneck -- but one that affected only males.

The difference was huge.  Zeng et al. showed that the disparity would only make sense if there was a point about seven thousand years ago when there was one male with surviving descendants for every seventeen females.

Feldman writes, in a press release to EurekAlert!:

After the onset of farming and herding around 12,000 years ago, societies grew increasingly organized around extended kinship groups, many of them patrilineal clans - a cultural fact with potentially significant biological consequences. The key is how clan members are related to each other.  While women may have married into a clan, men in such clans are all related through male ancestors and therefore tend to have the same Y chromosomes.  From the point of view of those chromosomes at least, it's almost as if everyone in a clan has the same father. 

That only applies within one clan, however, and there could still be considerable variation between clans.  To explain why even between-clan variation might have declined during the bottleneck, the researchers hypothesized that wars, if they repeatedly wiped out entire clans over time, would also wipe out a good many male lineages and their unique Y chromosomes in the process.

So as weird as it sounds, if you go back a few thousand years, we all have far fewer unique male ancestors than unique female ancestors.


Last, I would be remiss if I didn't make at least a brief mention of research that appeared in the Journal of Clinical Endocrinology and Metabolism last week.  Authored by Audrey J. Gaskins, Rajeshwari Sundaram, Germaine M. Buck Louis, and Jorge E. Chavarro, the paper was entitled "Seafood Intake, Sexual Activity, and Time to Pregnancy," and amongst its conclusion was that the quantity of seafood eaten correlates positively with the number of times per month people have sex.

The researchers speculate that the reason may be the higher quantity of long-chain omega-3 fatty acids, common in seafood, has an effect on the reproductive hormones, increasing sex drive.  It does, however, make me wonder how anyone thought of correlating these, but my puzzlement is probably indicative of why I never went into research.

In any case, I thought it was interesting.  And makes me glad I brought leftover scampi for lunch.  Hope springs eternal, you know?

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This week's recommended book is one that blew me away when I first read it, upon the urging of a student.  By groundbreaking neuroscientist David Eagleman, Incognito is a brilliant and often astonishing analysis of how our brains work.  In clear, lucid prose, Eagleman probes the innermost workings of our nervous systems -- and you'll learn not only how sophisticated it is, but how easy it can be to fool.