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.

Recently, 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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Bugs of unusual size

Although you don't tend to hear much about it, the Ordovician Period was a very peculiar time in Earth's history.

From beginning (485 million years ago) to the end (444 million years ago) it experienced one of the biggest global climatic swings the Earth has ever seen.  In the early Ordovician the climate was a sauna -- an intense greenhouse effect caused the highest temperatures the Paleozoic Era would see, and glacial ice all but vanished.  By the end, the center of the supercontinent of Gondwana was near the South Pole, and glaciers covered much of what is now Africa and South America, resulting in a massive extinction that wiped out an estimated sixty percent of life on Earth.

At this point, life was confined to the oceans.  The first terrestrial plants and fungi wouldn't evolve until something like twenty million years after the beginning of the next period, the Silurian, and land animals only followed after that.  So during the Ordovician, the shift in sea level had an enormous impact -- as the period progressed and more and more ocean water became locked up in the form of on-land glacial ice, much of what had been shallow, temperate seas dried up to form cold, barren deserts.

But during the beginning of the period, life thrived in the warm oceans, giving rise to huge ecosystems based on reef-building corals and sponges.  Just as today, back then coral reefs provided habitats to a tremendously diverse community, and fossil beds like the Fezouata Formation of Morocco give us a glimpse of a strange and wonderful world.

Here's one of the exceptionally well-preserved fossils from Fezouata, a marrellomorph arthropod called Furca mauritanica:

[Image licensed under the Creative Commons Didier Descouens, Furca mauritanica MHNT, CC BY-SA 3.0]

And here's a reconstruction of another one from the same group, the bizarre Mimetaster hexagonalis (the genus name means "mimics a starfish"):

[Image licensed under the Creative Commons Franzanth, Mimetaster hexagonalis reconstruction, CC BY-SA 4.0]

These arthropods, more closely related to trilobites than to any living species, were one of the dominant groups during the temperate early Ordovician, but had vanished almost entirely during the icehouse conditions of the end of the period.  

The reason this comes up is because of a paper out of the University of Exeter about further research into the fossils of the Fezouata Formation.  And this study has turned up something phenomenal -- another kind of marrellomorph arthropod related to Furca and Mimetaster that was something on the order of two meters long.

That is one big swimming bug.

I found this a little surprising, above and beyond simply being shocking because it's enormous.  As far as I understand physical chemistry, I would think that the greenhouse conditions of the early Ordovician implied two things: (1) higher carbon dioxide and lower oxygen levels, both in the atmosphere and the oceans; and (2) the warmer temperatures making what oxygen there was less soluble in water.  Both of these would lead to more hypoxic conditions, and -- again, as far as my layperson's understanding goes -- should result in generally smaller body size, especially in arthropods.

Arthropods have a couple of limitations that keep cockroaches from getting big as elephants (despite what you might have seen in any number of bad 1950s horror movies).  First, they aren't built to support a large body mass; a terrestrial insect expanded to enormous size, with its bodily proportions left intact, wouldn't be able to stand up, much less move.  This disadvantage is somewhat offset by living in the water, where buoyancy supports the body's mass.  (Note how much bigger oceanic mammals can get than terrestrial ones do.)

Second, and more apposite to this discussion, arthropods are limited by their rather shoddy respiratory systems.  They don't circulate oxygen using their blood, as we do; oxygen is absorbed passively, through channels called tracheal tubes (in terrestrial arthropods) and feathery gills (in aquatic ones).  Gills do have an edge, efficiency-wise, over tracheal tubes, but are working against water's much lower oxygen concentration (way less than one percent, as compared to air at sea level, which averages around twenty-one percent).  This is why terrestrial animals drown; their lungs are just not efficient enough to extract oxygen from a fluid that has so little of it.

And, as I said before, the likelihood is that the conditions of the early Ordovician would likely have combined to cause a far lower dissolved concentration in the oceans than we have now.

So how did marrellomorphs get so big?

At the moment, we don't know.  But the new study has shown that the early Ordovician seas were even weirder than we'd thought, with arthropods swimming around as long as a fully-grown human is tall.

No idea what those things ate, but if I ever get in a time machine and go back then, I'm sure as hell going to be careful if I go swimming.

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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.

 **********************************

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!]

Insect rebound

I vividly recall my first visit to the American Museum of Natural History in Washington, DC, perhaps fifteen years ago.  Having a fascination for evolutionary biology and paleontology, I was thrilled to take a walk down the hallway with exhibits of each biological taxon, in phylogenetic order -- put simply, all the groups of living things in the order they come on the family tree of life.

So I'm walking up the hall, and things are progressing the way I'd expect -- bacteria to protozoans to plants to primitive animals, and within Kingdom Animalia, jellyfish to flatworms to roundworms to more complex invertebrates, and then on to fish, amphibians, reptiles, birds, and mammals.

But that wasn't the end of the hall.  The usual approach to the "Great Tree of Life" -- with, of course, mammals at the top of the heap and humans at the top of the mammals, as befits the pinnacle of evolution -- wasn't applied here.  If you progress past mammals, you're into Phylum Arthropoda, those animals with jointed legs and an exoskeleton, which include arachnids, crustaceans, centipedes, millipedes, and the most successful creatures on Earth...

... insects.

Being that it's the end of summer in upstate New York, I can verify that insects are highly successful life forms, given that there are millions of mosquitoes in my back yard alone, every single one of which divebombs my wife whenever she goes outside.  Something about Carol just attracts biting insects.  In fact, she claims that I bring her along to tropical destinations just to draw the mosquitoes away from me.

Which is not true.  Honestly.

In all seriousness, there is incredible diversity amongst insects, and many taxonomists believe that the number of insect species outnumbers all other kinds of animals put together.  Just beetles by themselves -- Order Coleoptera -- represents over 400,000 species, or about 25% of the total animal biodiversity on Earth.

This is the origin of the famous story about biologist J. B. S. Haldane, who was not only a vocal proponent of evolution but was an outspoken atheist.  Haldane frequently had hecklers show up at his talks, and one such asked him at the end, "So, Professor Haldane, what has your study of biology told you about the nature of God?"

Without missing a beat, Haldane replied, "All I can say is that he must have an inordinate fondness for beetles."

Metallic Shield Bug (Scutiphora pedicellata) from Australia [Image licensed under the Creative Commons Benjamint444, Metallic shield bug444, CC BY-SA 3.0]

It's curious that such a diverse and ubiquitous group still has a great many questions unresolved about its origins.  It's known that the big jump in insect diversity came after the Permian-Triassic Extinction of 252 million years ago, the "Great Dying" that wiped out (by some estimates) 95% of life on Earth.  There's a common pattern that a sudden burst of species formation always follows a mass extinction, but in this case, because of a poor fossil record following the event, it's been hard to connect later biodiversity to speciation amongst the survivors.

We just got a huge boost in what we know about insect evolution because of the discovery of a fossil deposit in China dating from 237 million years ago, or only ("only!") fifteen million years after the extinction itself.  The site had eight hundred fossils representing 28 different insect families that had survived the bottleneck, including the ancestors of modern beetles, flies, and cockroaches.

The study, done jointly by Zheng Daran and Wang Bo of the State Key Laboratory of Paleobiology and Stratigraphy in Nanjing, China and Chang Su-Chin of the University of Hong Kong, is only a preliminary analysis of the fossils at the site, and has already helped to connect the dots between pre-Permian-Triassic insects and more modern ones.  As Elizabeth Pennisi, senior correspondent for Science magazine, writes:

The sites underscore that this burst of evolution took place much earlier than researchers had thought, particularly for water-loving insects.  Among the remains are fossil dragonflies, caddisflies, water boatmen, and aquatic beetles.  Until now, paleontologists had thought such aquatic insects didn’t diversify until 130 million years ago.  These insects—which include both predators and plant eaters—helped make freshwater communities more complex and more productive... moving them toward the ecosystems we see today.

It's always fascinating when we add something to our knowledge of past life, and even more impressive when it's about one of the most diverse groups that has ever existed.  Seeing how life rebounded after the Permian-Triassic Extinction should also give us hope -- that even after a cataclysm, the survivors can still come back and rebuild Earth's biodiversity.

Or, as Ian Malcolm put it in Jurassic Park, "Life finds a way."

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This week's Skeptophilia book recommendation is part hard science, part the very human pursuit of truth.  In The Particle at the End of the Universe, physicist Sean Carroll writes about the studies and theoretical work that led to the discovery of the Higgs boson -- the particle Leon Lederman nicknamed "the God Particle" (which he later had cause to regret, causing him to quip that he should have named it "the goddamned particle").  The discovery required the teamwork of dozens of the best minds on Earth, and was finally vindicated when six years ago, a particle of exactly the characteristics Peter Higgs had described almost fifty years earlier was identified from data produced by the Large Hadron Collider.

Carroll's book is a wonderful look at how science is done, and how we have developed the ability to peer into the deepest secrets of the universe.

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