Top of the heap

I don't understand why, amongst prehistoric animals, dinosaurs get all the attention.

Don't get me wrong, I like dinosaurs just fine, but there are so many others that are insanely cool.  

Many of which would be no fun to meet close-up.

Take, for example, the gorgonopsians, that had their heyday in the mid to late Permian Period.  These creatures were serious badasses -- apex predators that predated most of the dinosaurs, and which actually are a sister clade to the one containing mammals (Cynodontia), making them far more closely related to us than they are to a velociraptor.  The name means "looks like a Gorgon" -- referring, of course, to the terrifying monster from Greek mythology.

[Image licensed under the Creative Commons Mario Lanzas, Inostrancevia reconstruction, CC BY-SA 4.0]

The above shows a size comparison between Inostrancevia, one of the largest gorgonopsians, and a human.  You have to wonder why this guy is willing to walk right behind it like that, hands in his jacket pockets, whistling a tune.  Of course, I'm reminded of observing human behavior around bison, elk, and even once a juvenile grizzly bear, when I was in Yellowstone National Park, where many people seemed to think the place was an enormous petting zoo.  We talked to an exasperated ranger, who told us that his main job in the park was "keeping stupid tourists from committing suicide by wild animal."

But I digress.

Anyhow, the selective pressures on carnivores triggered something like convergent evolution between the gorgonopsians and (much more recent) animals like saber-toothed cats.  Gorgonopsians had elongated canine teeth and serrated molars, perfect for killing and slicing up prey.  The jaw morphology indicated that they had something like a ninety-degree gape, allowing for an enormous bite force when they closed.

Inostrancevia latifrons, attacking what is about to be an ex-Scutosaurus [Image licensed under the Creative Commons Creator: Dmitry Bogdanov, Inostranc lati2DB, CC BY 3.0]

Gorgonopsian fossils have been found primarily in two places -- Russia and South Africa.  While they're pretty distant from each other now, keep in mind that in the Permian, they (and every other land mass on Earth) were a lot closer:

[Image licensed under the Creative Commons Massimo Bernardi, MUSE, Trento, Italy. Published by Michael J. Benton., Permian–Triassic paleoclimate, CC BY 4.0]

The gorgonopsians were the top-tier carnivores for over twenty million years -- which, to put it in perspective, is around a hundred times longer than anatomically-modern humans have been in existence.  And who knows how long that hegemony would have lasted, and what direction history (well, prehistory) would have taken, but catastrophe was on the horizon.  The powder keg had been filled to overflowing during the preceding period, the Carboniferous, when high temperatures and precipitation had fostered the formation of enormous swaths of rain forest and swamp, leading to the accumulation of vast coal beds.  The climate had been drying out through the entire Permian, but the fuse was lit with the eruption of the Siberian Traps, the biggest volcanic eruption ever recorded.  The outpouring of lava ripped through the coal seams, depleting oxygen and dumping gigantic amounts of carbon dioxide into the atmosphere, and spiking the global average temperature by an estimated fourteen degrees Celsius.

The result: 95% of life on Earth became extinct, including the gorgonopsians.  The biggest, meanest, most badass predators of the Permian were one of the many groups that didn't survive the cataclysmic bottleneck between the Permian and Triassic Periods.

What did survive was the group that was to dominate everything for the next 180 million years -- the dinosaurs.  And, obviously, our own ancestors, the cynodonts, who at that point were pretty much small, scurrying, shrew-like beasts that a visitor to Earth wouldn't think could ever amount to much.  But as you know, the dinosaurs had their heyday come to a sudden, unexpected, and violent end as well, 66 million years ago.

Just shows that nothing stays on top forever -- something our policymakers might do well to heed, because we're the only animals on Earth that have the intelligence to recognize that what we're doing might endanger our own survival, and potentially do something about it.

We're not immune to the fates of other groups that, in their time, seemed like they'd be permanently on the top of the heap.  

Let's hope we can learn from our planet's past history.

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Creepy crawlies

Whenever we have a wet summer -- not an uncommon occurrence in our rainy climate -- we have a plague of little pests trying to get into our house.

They're called millipedes, slinky guys maybe a couple of centimeters long, with lots of legs (not a thousand, though).  They're completely harmless; they don't bite like their cousins the centipedes do, and if you poke at them, they coil up into a ball.  So I guess they're really more of a nuisance than an actual problem.  They don't even damage anything, the way mice can.  Mostly what they seem to do is get in through every crack and crevice (there are lots of these in a big old house like ours), look around for a while, then curl up and die.

[Image licensed under the Creative Commons Totodu74, Anadenobolus monilicornis 03, CC BY-SA 3.0]

So I don't like them, and I wish they stayed outside, but in the grand scheme of things they're no big deal.  Imagine, though, if they were bigger.

A lot bigger.

Just last week, paleontologists announced the discovery on a beach in Northumberland, England, of a millipede fossil from the Carboniferous Period.  It's been dated to the middle of the period, about 326 million years ago.  It looks a bit like the millipedes I see trundling across my basement floor in summer.

Only this one was 2.6 meters long (approximately the length of a Mini Cooper), a half a meter across, and weighed something on the order of fifty kilograms.

It's been named Arthropleura, and holds the record as the largest-known arthropod in Earth's history.  Nothing is known for sure about its behavior; if it's like the rest of millipedes, it was a scavenger on leaf detritus, but there's no way to know for certain.  Given its size, it could well have been a lot more dangerous than the ones we have around now.  To paraphrase the old joke about five-hundred-pound gorillas:

Q:  What does a fifty-kilogram millipede eat?

A:  Anything it wants.

Those of you who are (like me) biology nerds may be frowning in puzzlement at this point.  How on earth could an arthropod get so big?  Their size is limited by the inefficiency of their respiratory system (not to mention the weight of their exoskeletons).  Most arthropods (millipedes included) breathe through pairs of holes called spiracles along the sides of the body.  These holes open into a network of channels called tracheae, which bring oxygen directly to the tissues.  Contrast that with our system; we have a central oxygen-collecting device (lungs), and the hemoglobin in our blood acts as a carrier to bring that oxygen to the tissues.  It's a lot more efficient, which is why the largest mammals are a great deal bigger than the largest arthropods.  (So, no worries that the bad sci-fi movies from the 50s and 60s, with giant cockroaches attacking Detroit, could actually happen.  A ten-meter-long cockroach not only wouldn't be able to oxygenate its own tissues fast enough to survive, it couldn't support its own weight.  It wouldn't eat Detroit, it would just lie there and quietly suffocate.)

So how could there be such ridiculously enormous millipedes?

The answer is as fascinating as the beast itself is.  As the temperature warmed and rainfall increased after the previous period (the Devonian), it facilitated the growth of huge swaths of rain forest across the globe.  In fact, it's the plant material from these rain forests that produced the coal seams that give the Carboniferous its name.  But the photosynthesis of all these plants drove the oxygen levels up -- by some estimates, to around 35% (contrast that to the atmosphere's current 21% oxygen).  This higher oxygen level facilitated the growth of animals who are limited by their ability to uptake it -- i.e., arthropods.  (At the same time, there was a dragonfly species called Meganeura with a seventy-centimeter wingspan.  And unlike millipedes, these things were carnivores, just as modern dragonflies are.)

Eventually, though, the system was unsustainable, and a lot of the rain forests began to die off in the Late Carboniferous, leading to a drier, cooler climate.  However, remember the coal seams -- by that time a huge percentage of the carbon dioxide that had fed the photosynthesis of those rain forests was now locked underground.  The fuse was lit for a catastrophe.

Fast forward to the end of the next period, the Permian, 255 million years ago.  What seems to have happened is a series of colossal volcanic eruptions that created the Siberian Traps, a basalt deposit covering most of what is now Siberia.  The lava ripped through the coal seams, blasting all that stored carbon into the atmosphere as carbon dioxide.  The temperature in the late Permian had been cool and dry, and the spike of carbon dioxide created a commensurate spike in the temperature -- as well as a huge drop in oxygen, used up by the burning coal.  The oxygen concentration seems to have bottomed out at around twelve percent, just over half of what it is now.  The extra carbon dioxide dissolved into ocean water, dropping the pH, and the increasing acidity dissolved away the shells of animals who build them out of calcium carbonate -- e.g. corals and mollusks.

Wide swaths of ocean became anoxic, acidic dead zones.  The anaerobic organisms began to eat through all the dead organic matter, churning out more carbon dioxide and another nasty waste product, sulfur dioxide (which gives the horrible smell to rotten eggs, and is also an acidifier).  The result: an extinction that wiped out an estimated ninety percent of life on Earth.  In short order, a thriving planet had been turned into a hot, dead, foul-smelling wasteland, and it would take millions of years to recover even a fraction of the previous biodiversity.

Of course, at highest risk would be the big guys like our friends Arthropleura and Meganeura, and the Earth hasn't seen giant arthropods like this since then.  Today, the largest arthropod known is the Japanese spider crab (Macrocheira), topping out at around twenty kilograms -- but crabs and other crustaceans have gills and an oxygen carrier called hemocyanin, so they can boost the efficiency of their respiratory system somewhat over their terrestrial cousins.  The largest insect today is the African Goliath beetle (Goliathus), at about a tenth of a kilogram.  And in today's atmosphere, it's at a pretty significant disadvantage.  They may look big and scary, but in reality, they're slow-moving, harmless creatures.  Kind of a beer can with six legs, is how I think of them.

So that's today's look at creepy-crawlies of the past.  In my opinion it's just as well the big ones became extinct.  The last thing I need is having to shoo a fifty-kilogram millipede out of my basement.

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Neil deGrasse Tyson has become deservedly famous for his efforts to bring the latest findings of astronomers and astrophysicists to laypeople.  Not only has he given hundreds of public talks on everything from the Big Bang to UFOs, a couple of years ago he launched (and hosted) an updated reboot of Carl Sagan's wildly successful 1980 series Cosmos.

He has also communicated his vision through his writing, and this week's Skeptophilia book-of-the-week is his 2019 Letters From an Astrophysicist.  A public figure like Tyson gets inundated with correspondence, and Tyson's drive to teach and inspire has impelled him to answer many of them personally (however arduous it may seem to those of us who struggle to keep up with a dozen emails!).  In Letters, he has selected 101 of his most intriguing pieces of correspondence, along with his answers to each -- in the process creating a book that is a testimony to his intelligence, his sense of humor, his passion as a scientist, and his commitment to inquiry.

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

Relics of a lost age

If I can be allowed to geek out a little, today's post is about two new discoveries in the field of paleontology.

The mid-Permian period was (1) a challenging time to live, when the climate was rapidly warming and drying, and (2) at 270 million years before the present, was a really long time ago.  Not only was the climate getting dicey, the world was heading for catastrophe -- the lockup of the supercontinent Pangaea, as all the world's land masses fused into one and the rest of the Earth was covered by a giant ocean, is thought to have been the kickoff to the largest wipeout the Earth has ever seen -- the Permian-Triassic extinction.  Not only did the formation of the supercontinent (and superocean) 252 million years ago drastically change the climate, the event coincided with the formation of the Siberian Traps, when four million cubic kilometers of basaltic lava flowed out over what is now eastern Russia.  The resulting massive burning of organic matter spiked the carbon dioxide content of the atmosphere, simultaneously causing the oxygen content to crash and triggering a warm-up that resulted in average ocean surface temperatures of 40 C (104 F).

The result: 95% of the species on Earth became extinct.

Of course, one of the lineages that made it through the bottleneck was our own ancestors.  Back in the mid-Permian -- pre-mass-extinction -- there was a group of protomammals called Gorgonopsians, which included some seriously scary carnivores (one, Inostrancevia, had a 45-centimeter-long skull and saber teeth -- preceding the more famous "saber-toothed tiger" Smilodon by a good 260 million years).

Permian protomammal fossils are quite rare, however.  So it's pretty awesome that paleontologist Christian Kammerer, paleontology curator of the North Carolina Museum of Natural Sciences, discovered fossils of not one, but two new species of mid-Permian protomammals in a small museum in Russia.

Called Gorynychus matsyutinae and Nochnitsa geminidens, the two were drastically different in size.  Gorynychus was probably one of the apex predators of its time, with a 25-centimeter-long skull and big, nasty, pointy teeth.  Nochnitsa, also a predator, was weasel-sized.  The genera were both named after beasts from Russian mythology -- the three-headed dragon Zmey Gorynych and the malevolent, vampiric night spirit Nochnitsa.

Artist's reconstruction of Gorynychus and Nochnitsa [by Matt Celeskey @clepsydrops, from the press release from the North Carolina Museum of Natural Sciences; used with permission]

These lineages both made it through the bottleneck, but not unscathed.  Their descendants, eighteen or so million years later, underwent some rapid evolution during the Permian-Triassic extinction, especially with respect to size.  "In the age before the dinosaurs, when protomammals were the dominant life on land, you had two different groups that switch off on which is the top predator," Kammerer said.  "You have wolf- to lion-sized saber tooth animals wiped out by a mass extinction, and [the Nochnitsa-like animals] take over.  But [Gorynychus-like animals] aren’t wiped out altogether in this extinction, and they take over and become a small insect eating predator, not large carnivores anymore."

Kammerer and his co-author (and co-discoverer of the fossils), Vladimir Matsyutin of the Vyatka Paleontological Museum of Kirov, Russia, were excited not only about having found fossils of two hitherto-unknown species, but about the potential for other discoveries tucked away in museums.  "I would guarantee you there are thousands of undescribed species in museum collections,” Kammerer said.  "Most new species are found in museum collections for the sole reason that there are literally millions of species on Earth today and many more in the fossil record.  When you’re going out and collecting specimens, you won’t know those things.  The people in the museum knew they were protomammals but they didn’t know they were new species."

So that's today's cool science story, about some of our (very) distant relatives.  I've always been fascinated with the early mammals -- for some reason, much more than the charismatic megafauna that were just getting their start at the same time (the dinosaurs, of course).  And the fact that these critters were out doing their thing as the Earth was heading toward the largest catastrophic extinction ever just adds a nice little frisson to the discovery.  You kind of want to warn them about what's coming, you know?

Oh, well, probably wouldn't have helped.  It's not like you can hide from four million cubic kilometers of lava.

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This week's recommended read is Wait, What? And Life's Other Essential Questions by James E. Ryan.  Ryan frames the whole of critical thinking in a fascinating way.  He says we can avoid most of the pitfalls in logic by asking five questions: "What?"  "I wonder..." "Couldn't we at least...?" "How can I help?" and "What truly matters?"  Along the way, he considers examples from history, politics, and science, and encourages you to think about the deep issues -- and not to take anything for granted.