Very like a mammal

"Prior to the End-Cretaceous Extinction, mammals were all small and shrew-like, restricted to skulking, scurrying forms because of competition from, and predation by, dinosaurs.  Once the dinosaurs were out of the way, the mammals were free to diversify and to grow larger."

How many times have we all heard this?  And it certainly sounds plausible; being large and obvious when there were hungry carnivores like Velociraptor around seems like a good way to be turned into dinner.

But the fossil record shows that the truth is more complicated -- and far more interesting.

Take, for example, Castorocauda lutrasimilis.  This animal was around fifty centimeters long and weighed in at around three-quarters of a kilogram.  It was sleek, streamlined, with a bullet-shaped head, a fine pelt of soft fur, and a flat, paddle-like tail.  Here's an artist's reconstruction:

[Image licensed under the Creative Commons Nobu Tamura (http://spinops.blogspot.com), Castorocauda BW, CC BY 3.0]

If you're reminded of something like a beaver or an otter, you're not alone; the scientific name means "beaver's tail and looks like an otter."  Surprisingly, it was closely related to neither one; in fact, it's not even a true mammal, but a docodont, which split off from other mammal-like forms (including our own ancestors) way back in the early Jurassic period -- while there were plenty of dinosaurs lumbering around the place.

The docodonts, and a handful of other groups of Mesozoic cousins to mammals, are mostly known from the exceptional fossil beds of the Tiaojishan Formation in northern China, where paleontologists have found a wealth of mid- to late-Jurassic fossils of mammaliaformes -- as they call Mesozoic mammals and their near relatives.  And amongst those fossils they not only find otter-like aquatic species, but ones that have adaptations an awful lot like moles, squirrels, and possums.

This adds another cluster to the list of cool examples of convergent evolution, where two only distantly-related species evolve to resemble each other superficially because of similar selective pressures.  (A famous modern pair is the North American flying squirrel and the Australian sugar glider; at a quick glance these two look very much alike, but a closer examination would show that they're not even in the same order.  The flying squirrel is a rodent, and the sugar glider a marsupial.)

The docodonts and other side branches of the mammaliaformes all disappeared by the middle of the Cretaceous Period, replaced by true mammals including multituberculates, monotremes, marsupials, and placentals.  Why this happened isn't certain; given that we know the non-mammal mammaliaformes from only a few isolated geological strata, our information on them is limited.  We do know, however, that the mammals who survived were mostly "small and shrew-like," so there's a grain of truth to the old model.

What's most fascinating is that after the End-Cretaceous Extinction, these survivors re-diversified, and "re-invented" a bunch of the adaptations the docodonts had a hundred million years earlier.  This has interesting implications, not only for the evolution of life on Earth but for the kinds of living things we might expect to find on other planets.  It's long been a fascinating question to me to what extent evolution is constrained -- what limitations there are on natural selection that might result in its generating the same patterns over and over because those are the features that work best in pretty much any environment.  There are a few that seem likely, such as having the main sensory organs near the mouth and at the anterior of the body; I'd expect those to be frequent no matter where you go.

But what Castorocauda and the other docodonts show is that other sorts of traits can repeat, too.  After all, there are only so many ways you can move around, find food, find shelter, avoid being eaten, and regulate your own body temperature.  It might be surprising at first that the otter-like Castorocauda (and the possum-like Borealestes and the squirrel-like Shenshou) "re-evolved" (as it were) over a hundred million years later, but it suggests that making a living requires the same toolkit pretty much regardless.  

So maybe when we find life on another planet, it'll be far more familiar than we expect -- and that "life as we know it, Jim" might be there to greet us when we arrive.

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A Jurassic wake-up call

About 183 million years ago -- during the Toarcian Age, one of the subdivisions of the early Jurassic Period -- there was a sudden and puzzling extinction.

Things had been recovering nicely after the End-Triassic Mass Extinction, eighteen million years earlier.  While dinosaurs were not yet at the peak they would hit in the later Jurassic, they were well on their way to taking over the place.  The temperatures were cool -- there's evidence of widespread glaciation during the ten million years prior -- but by and large, everything seemed to be coping just fine.

Then, suddenly, wipeout.

It wasn't as big as some of the truly dramatic mass extinctions the Earth has experienced, but that doesn't mean it was insignificant.  Marine invertebrates got clobbered, dropping both in diversity and in overall numbers.  Over ninety percent of coral species went extinct.  Two entire orders of brachiopods died; bivalves, ostracods, and ammonoids survived, but with greatly reduced populations.  Coelophysid and dilophosaurid dinosaurs got wiped out completely.  Seed ferns and lycophytes declined sharply, to be replaced by cycads and conifers.

Fossil seed fern [Image is in the Public Domain]

All of it occurred rapidly -- the current estimates are less than five hundred thousand years, which is a snap of the fingers geologically.

So what happened?

The culprit seems to have been the Karoo-Ferrar Large Igneous Province, an enormous volcanic formation (estimated at about three million square kilometers) now underlying much of southern Africa, eastern Antarctica, and southwestern South America.  At this point, Gondwana -- the southern half of the supercontinent of Pangaea -- had just begun to break up, and this massive series of eruptions was part of the process of rifting.  But what caused the extinction was not the eruption itself -- it was the sudden spike of atmospheric carbon dioxide, which swung the climate from a glacial period to a hothouse.  A study released last week by a team at Duke University found evidence of a twenty thousand gigaton carbon dioxide pulse, triggering not only a drastic temperature increase, but widespread ocean acidification and anoxia.

According to the study, during the event, eight percent of the global seafloor -- an area three times that of the United States -- became completely anoxic.  The pH dropped so much that animals with calcium carbonate exoskeletons literally dissolved.  Rainfall patterns shifted dramatically, impacting terrestrial biomes as well.  By the time things began to recover, it was a changed world, all in a matter of a half of a million years.

Ready for the punchline? 

Today's rate of carbon dioxide increase in the atmosphere is over two hundred times what it was during the Toarcian Extinction Event.

Twenty thousand gigatons in five hundred thousand years is a lot, and had a devastating effect on the world's ecosystems; we've put two thousand gigatons into the atmosphere in the past two hundred years.  

Is it any surprise why the scientists have been trying like hell to get everyone's attention?

"We just don't have anything this severe [in the geological record]," said paleoclimatologist Michael Kipp, who co-authored the study.  "We go to the most rapid CO2-emitting events we can in history, and they're still not rapid enough to be a perfect comparison to what we're going through today. We're perturbing the system faster than ever before.  We have at least quantified the marine oxygen loss during this event, which will help constrain our predictions of what will happen in the future."

None of this is meant to stun people into giving up.  We have got to get a handle on this.  Yes, we've crossed several benchmarks the climate scientists have warned us about.  But every tenth of a degree's further increase we can prevent will mitigate the effects of what we're doing.  We have got to stop electing politicians who shrug their shoulders about anthropogenic climate change, most strikingly Florida's belligerent and willfully stupid Governor Ron DeSantis, who recently signed a law striking any mention of climate change in state statutes, banning offshore wind turbines, and deregulating natural gas production, transport, and use.  

In one of the lowest-lying, most hurricane-prone states in the country.

Maybe it will take our getting slapped hard to wake us up; we don't have a good record of addressing problems that aren't right in front of our faces.  Events like the massive heat dome that just cooked the southern, central, and northeastern states are just the beginning, and are easily forgotten once they pass.  They're predicting a vicious hurricane season, fueled by a central Atlantic with a surface the temperature of bath water, but we've seen dire predictions before and gone on our way as if nothing was amiss.

So how many lives will it cost before that wake-up call is finally listened to?

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Wings over Skye

I know it seems like I keep ringing the changes on this topic over and over, but... it never fails to astonish me how much the Earth has changed over geologic history.

Part of my fascination, I think, comes from the fact that this knowledge is so at odds with how it feels to be an actual inhabitant of the planet.  When you look around, it seems like things are pretty static.  Oh, there are changes -- volcanoes and earthquakes come to mind -- but however catastrophic those can be for local residents, the fact remains that they are, on a planetary scale, tiny effects.  To see the big shifts requires a much longer time axis, but if you have the perspective of one...

... wow.

Take, for example, the discovery of new species of pterosaur in one of the last places I can picture a pterosaur flying -- the Isle of Skye, Scotland.  Now a cool, windswept, rocky island chain with few trees and lots of grass and heather, the Hebrides (and the rest of the British Isles) were, during the Jurassic Period, a lush subtropical land only separated from what would become North America and Greenland by a shallow strait of ocean.

The configuration of the continents at the mid-Jurassic [Image credit: Ron Blakey, NAU Geology]

And flying over the forests of Jurassic Scotland were some of the coolest prehistoric beasts ever, the pterosaurs.

Dubbed Ceoptera evansae -- the genus name means "mist flyer," from the Gaelic word ceò, mist, which also gives the Isle of Skye its Gaelic name of Eilean a'Cheò, "misty island" -- the newly-discovered fossil was found in the Kilmaluag Formation and dated to about 167 million years of age.  Ceoptera was a smallish pterosaur, measuring about sixty centimeters from beak to tail tip:

[Image credit: Elizabeth Martin-Silverstone et al., Journal of Vertebrate Paleontology]

The era when Ceoptera was flying over the Isle of Skye was a point of great diversification amongst the pterosaurs, a process which would accelerate during the rest of the Jurassic and into the Cretaceous, ultimately resulting in species from fifty-centimeter-long Sordes pilosus to the six-meter-wingspan Quetzalcoatlus northropi.  Eventually, however, the entire taxon would be wiped out in the Cretaceous-Tertiary Extinction of sixty-six million years ago.

"The time period that Ceoptera is from is one of the most important periods of pterosaur evolution, and is also one in which we have some of the fewest specimens, indicating its significance," said Elizabeth Martin-Silverstone of the University of Bristol, who led the study, in an interview with Science Daily.  "To find that there were more bones embedded within the rock, some of which were integral in identifying what kind of pterosaur Ceoptera is, made this an even better find than initially thought.  It brings us one step closer to understanding where and when the more advanced pterosaurs evolved."

For me, the coolest part is trying to picture what the world looked like back then.  Even with our knowledge of plate tectonics and the fossils we have available for study, we still have only the shadowiest image of the Jurassic world.  Consider what doesn't fossilize -- colors, sounds, smells, behavior.  We can make some guesses about what those were like based upon modern organisms, but guesses they will always be, and many of them significantly off the mark.  (If you want a good laugh some time, look into "prehistoric animals that were reconstructed wrong" and find out how wildly inaccurate even the experts can be.  Fortunately, science self-corrects, and the fact that we now know they were wrong comes from better fossils and more sophisticated analysis -- but even so, we still have a vague and incomplete picture of what things were really like back then.  Oh, for a time machine...)

So that's our flight of fancy for today.  Prehistoric wings over the Isle of Skye.  Makes you wonder what things will look like in another 160 million years or so.  We'll have a whole new set of "endless forms most beautiful and most wonderful," to use Darwin's trenchant words -- ones we could not even begin to predict.

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A new view of the "eye lizard"

I am forever astonished at the level of detail we can infer from fossils that are hundreds of millions of years old.

The most recent example of this came from analysis of a fossil of Stenopterygius, an ichthyosaur that lived during the Jurassic Period (this particular fossil has been dated to about 180 million years ago).  We usually think of fossils as preserving bones and teeth, and occasionally impressions of scales or skin or feathers -- but this one was so finely preserved that researchers have been able to make some shrewd inferences about color, metabolism, and the structure of soft tissues.

Artist's conception of Stenopterygius [Image licensed under the Creative Commons Nobu Tamura (http://spinops.blogspot.com), Stenopterygius BW, CC BY-SA 3.0]

We've known for a long time that ichthyosaurs are bizarre animals. They were streamlined predators that look remarkably like dolphins, although they are only distantly related (making the two groups a great example of convergent evolution).  A number of them had an even stranger feature, which is the largest eye-diameter-to-body-size ratio of any animal known -- the well-named Ophthalmosaurus (Greek for "eye lizard") was six meters long and had eyes the size of basketballs.

Stenopterygius was a bit smaller, with an average adult size of four meters.  But up until recently, all we've been able to do is speculate on what it might have looked like, and how it behaved.  A discovery in Germany, described in a paper in Nature called "Soft-Tissue Evidence for Homeothermy and Crypsis in a Jurassic Ichthyosaur" and authored by no fewer than 23 scientists, has given us incredibly detailed information on these oddball dinosaurs.

The authors write:

Ichthyosaurs are extinct marine reptiles that display a notable external similarity to modern toothed whales.  Here we show that this resemblance is more than skin deep.  We apply a multidisciplinary experimental approach to characterize the cellular and molecular composition of integumental tissues in an exceptionally preserved specimen of the Early Jurassic ichthyosaur Stenopterygius.  Our analyses recovered still-flexible remnants of the original scaleless skin, which comprises morphologically distinct epidermal and dermal layers.  These are underlain by insulating blubber that would have augmented streamlining, buoyancy and homeothermy.  Additionally, we identify endogenous proteinaceous and lipid constituents, together with keratinocytes and branched melanophores that contain eumelanin pigment.  Distributional variation of melanophores across the body suggests countershading, possibly enhanced by physiological adjustments of colour to enable photoprotection, concealment and/or thermoregulation.  Convergence of ichthyosaurs with extant marine amniotes thus extends to the ultrastructural and molecular levels, reflecting the omnipresent constraints of their shared adaptation to pelagic life.

So from a 180-million-year-old fossil, we now know that Stenopterygius (1) was a homeotherm (colloquially called "warm-blooded"), (2) had a blubber layer much like modern dolphins and whales, and (3) were countershaded -- dark on top and light underneath, to aid camouflage -- similar to dozens of species of modern fish.

This level of preservation is extremely unusual.  "Both the contour of the body and the remains of internal organs are clearly visible," said paleontologist Johan Lindgren of the University of Lund, who co-authored the paper.  "Surprisingly, the fossil is so well preserved that it is possible to observe individual cell layers inside the skin."

"This is the first direct chemical evidence of warm blood in an ichthyosaur, because a subcutaneous fat layer is a characteristic of warm-blooded animals," said Mary Schweitzer of North Carolina State University, also a co-author.  "Ichthyosaurs are interesting because they have many features in common with dolphins, but they are not related at all to these mammals that inhabit the sea.  But the enigma does not stop there...  They have many characteristics in common with living marine reptiles, such as sea turtles; but we know from the fossil record that they gave live birth to their young...  This study reveals some of those biological mysteries."

Which is pretty astonishing.  I've always had a fascination for the prehistoric world, and have spent more time than I like to admit wondering what it might have been like to live in the Jurassic world. This research gives us one more piece of information -- about a fierce prehistoric predator that shared some amazing similarities to creatures that still swim in our oceans.

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Jurassic rainbow

Regular readers of Skeptophilia might recall that about a year ago, paleontologists announced the discovery of a bird fossil from northeastern China that had a long, pennant-like tail -- and that from the extraordinary state of preservation, they were able to determine that the outer tail feathers had been gray, and the inner ones jet black.

Determining feather, hair, and skin color of prehistoric animals is remarkably tricky; the pigments in those structures break down rapidly when the animal's body decomposes, and the structures themselves are fragile and rarely fossilize.  The result is that when artists do reconstructions of what these animals may have looked like, they base those features on analogies to modern animals.  This is why in old books on dinosaurs, they were always pictured as having greenish or brownish scaly skin, like the lizards they were thought to resemble, even though dinosaurs are way more closely related to modern birds than they are to modern lizards.  (To be fair, even the paleontologists didn't know that until fairly recently, so the artists were doing their best with what was known at the time.)

But it does mean that if we were to get in the TARDIS and go back to the Mesozoic Era, we'd be in for a lot of surprises about what the wildlife looked like back then.  Take, for example, the late Jurassic Period fossil found by a farmer in China that contained the nearly-complete skeleton of a birdlike dinosaur.  Here's the fossil itself:

What's remarkable about this fossil is that the feathers were so well-preserved that paleontologists were able to get a close look at the melanocytes -- the pigment-containing cells -- and from the arrangement and layering of those cells, they determined that the dinosaur's head feathers were arrayed like a rainbow, similar to modern hummingbirds, sunbirds, and trogons.

So here's the current reconstruction of what this species looked like:

[Reconstruction by artist Velizar Simeonovski, of The Field Museum]

Kind of different from the drab-colored overgrown iguanas from Land of the Lost, isn't it?

The species, christened Caihong juji from the Mandarin words meaning "big rainbow crest," adds another ornate member to the late Jurassic and early Cretaceous fauna of what is now northern China.  And keep in mind that we only know about the ones that left behind good fossils -- probably less than one percent of the total species around at the time.  As wonderful as it is, our knowledge of the biodiversity of prehistory is analogous to a future zoologist trying to reconstruct our modern ecosystems from the remains of a sparrow, a cat, a raccoon, a deer, a grass snake, and a handful of leaves from random plants.

I think my comment about being "in for a lot of surprises" if we went back then is a significant understatement.

Even so, this is a pretty amazing achievement.  Astonishing that we can figure out what Caihong juji looked like from some impressions in a rock.  And it gives us a fresh look at a long-lost world -- but one that was undoubtedly as rainbow-hued and iridescent as our own.

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Dinosaur redux

For me, one of the coolest things about science is that even once you think you've got something pretty well figured out, you can always find new interesting pieces of the puzzle.

For example, take dinosaurs, which we've known a good bit about for a long while, starting with Mary Anning's discoveries along the "Jurassic Coast" of Dorset, England in the early nineteenth century.  Even the kids' books when I was growing up back in the 1960s and 1970s had a lot of pretty decent information.  Although some of the reconstructions of skeletons, and (especially) our knowledge of the soft tissue that covered it, has changed since that time, it wasn't like I had to completely relearn the science when I studied it more seriously.

That said, we're still learning new stuff and adding to the picture.  Just this week we had two new papers that have sharpened the focus on our understanding of dinosaur evolution -- the first about the mid-Jurassic peak in dinosaur diversity and size, and the second about the event that wiped the entire lineage out, with the exception of the ones we now call birds.

The first paper is from Proceedings of the Royal Society B, and is titled "Extinction of Herbivorous Dinosaurs Linked to Early Jurassic Global Warming Event."  The paper was written by a team led by Diego Pol, paleontologist at the Paleontological Museum Egidio Feruglio in Trelew, Argentina, and looked at a hitherto-unexplained overturning of Jurassic fauna that made way for the rise of the sauropods -- the largest land animals that have ever lived.

Skeleton of Apatosaurus [Image licensed under the Creative Commons Tadek Kurpaski from London, Poland, Louisae, CC BY 2.0]

The early Jurassic had a high dinosaur diversity, but then toward the middle of the period something happened, and a good many of the early Jurassic dinosaurs vanished.  They were replaced by behemoths like the familiar Brachiosaurus and the less-well-known but hilariously-named Supersaurus, which measured an almost unimaginable 33 meters from tip to tail.  (Even better, though, is the name Dreadnoughtus, which was shorter than Supersaurus -- "only" 26 or so meters long -- but is thought to be the heaviest land animal ever, on the order of thirty metric tonnes.)

So what caused the replacement of the earlier species by the giants?  Pol and his team found what they think is the smoking gun, a series of massive volcanic eruptions in southern Gondwanaland (what is now South America and Africa), which spiked the carbon dioxide content of the air, boosting the average temperature and dropping the pH of ocean water.  

The perturbation of the climate affected the plants first.  Earlier groups, like seed ferns and other smaller herbaceous plants, were replaced by conifers, which have tough, lignified stems, small needles or scales instead of leaves, and thick waxy cuticles to prevent water loss.  The problem is -- if you're an early Jurassic herbivorous dinosaur -- having evolved to eat seed ferns, you're not going to do so well trying to munch pine needles.

So as it always does, the change to the base of the food web percolated its way up to the top.  The early dinosaurs were replaced by big sauropods, who had grinding teeth (so tough plant material could be thoroughly pulverized before swallowing) and large stomachs (where food could sit and digest for a long time, extracting all the nutritive value possible).  The result was the arrival on the scene of monsters like Supersaurus and Dreadnoughtus and their cousins, which were the dominant land herbivores for a good hundred million years thereafter.

Sometimes new evidence results in our having to revise our previous models, overturning what we thought we knew.  Take, for example, the research that appeared this week in Royal Society Open Science that conclusively put to rest a commonly-held idea -- that by the time the Chicxulub Meteorite hit the Earth 66 million years ago, dinosaurs were already in a steep decline, so they would have disappeared anyhow, even without the massive impact that was the final death blow.

In "Dinosaur Diversification Rates Were Not in Decline Prior to the K-Pg Boundary," by a team led by Joseph Bonsor of the London Natural History Museum and the University of Bath, we find out that the dinosaurs were actually doing okay before the meteorite hit.  Far from being in decline, they would have been very likely to retain their position as the dominant animals on Earth well into the Cenozoic Era -- with effects on mammalian evolution that can only be imagined.

Bonsor, as befits a good scientist, is cautious about overconcluding.  "The main point of what we are saying is that we don't really have enough data to know either way what would have happened to the dinosaurs," Bonsor said in a press release from the Natural History Museum.  "Generally in the fossil record there is a bias towards a lack of data, and to interpret those gaps in the fossil record as an artificial decline in diversification rates isn't what we should be doing.  Instead we've shown that there is no strong evidence for them dying out, and that the only way to know for sure is to fill in the gaps in the fossil record."

But in the absence of positive evidence for a decline, we're thrown back to the null hypothesis; that they weren't in imminent danger of extinction.  So the whole idea of the dinosaurs as some kind of "failed experiment" in evolution is clearly wrong.  Not only did they kind of run things for a good two hundred million years -- which, by comparison, is something like a thousand times longer than we've been around -- they would probably have persisted for a good long while had a giant rock not interfered.

Me, I always want to know "what if?"  I think it comes from being a novelist; I'm always wanting to play around with reality and see what happens.  If the dinosaurs had stuck around for a long time rather than dying out 66 million years ago, it's hard to see how the rise of mammals -- and ultimately, us -- would have occurred.  Mammals had been around for a long while before the Chicxulub Impact, but they were mostly small, presumably kept that way both by the big carnivores and by competition with herbivores much larger than themselves.  So what would the Earth look like today?

Super-intelligent dinosaurs?  Maybe.  Evolution doesn't always point in the direction of "bigger and smarter;" it's the law of whatever works.  So as fun as it is to speculate, to be fair we have to side with Bonsor and say we just don't know.

Anyhow, that's our look back into the distant past for today.  Cool that we're still assembling new views of an old branch of biology.  Further reinforcing my opinion that if you're interested in science, you will never ever be bored.

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This week's Skeptophilia book-of-the-week is one that has raised a controversy in the scientific world: Ancient Bones: Unearthing the Astonishing New Story of How We Became Human, by Madeleine Böhme, Rüdiger Braun, and Florian Breier.

It tells the story of a stupendous discovery -- twelve-million-year-old hominin fossils, of a new species christened Danuvius guggenmosi.  The astonishing thing about these fossils is where they were found.  Not in Africa, where previous models had confined all early hominins, but in Germany.

The discovery of Danuvius complicated our own ancestry, and raised a deep and difficult-to-answer question; when and how did we become human?  It's clear that the answer isn't as simple as we thought when the first hominin fossils were uncovered in Olduvai Gorge, and it was believed that if you took all of our millennia of migrations all over the globe and ran them backwards, they all converged on the East African Rift Valley.  That neat solution has come into serious question, and the truth seems to be that like most evolutionary lineages, hominins included multiple branches that moved around, interbred for a while, then went their separate ways, either to thrive or to die out.  The real story is considerably more complicated and fascinating than we'd thought at first, and Danuvius has added another layer to that complexity, bringing up as many questions as it answers.

Ancient Bones is a fascinating read for anyone interested in anthropology, paleontology, or evolutionary biology.  It is sure to be the basis of scientific discussion for the foreseeable future, and to spur more searches for our relatives -- including in places where we didn't think they'd gone.

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

A bone to pick

Dear Skeptophiles,

This is just to let you know that I'll be going on a wee hiatus to attend the annual Writers' Retreat held by my publisher, Oghma Creative Media, in the lovely Ozark Mountains.  So I'll be away for two weeks, and will be back in the saddle on Monday, August 12.  Please keep sending me ideas and links, making comments on posts, and so on -- I always love hearing from my readers.

Until then, hoist high the banner of skepticism!

cheers,

Gordon

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The lovely thing about science is that you never have a reason to stop learning.

I just retired after teaching biology for 32 years, and the area of biology I studied the most (and enjoyed teaching the most) was evolution and phylogeny.  I'm not a researcher, and nowhere near a specialist (I've been called a "dabbler" and a "dilettante," and I don't think they were meant as compliments), but I think that about those topics I'm at least Better Than the Average Bear.

So I was a little surprised yesterday to run into a group of ancient mammals I had honestly never heard of.  They're called docodonts, and technically I misspeak by calling them "mammals;" they're mammaliforms, which sounds like a species of alien on Doctor Who but isn't.  The docodonts and other mammaliforms are cousins of modern mammals, seem to have left no living descendants, and are more like mammals than they are like any other extant group.  Take, for example, this docodont, Castorocauda (the name means "beaver-tail"):

[Image licensed under the Creative Commons Nobu Tamura (http://spinops.blogspot.com), Castorocauda BW, CC BY 3.0]

Of course, like the proto-bird-with-teeth we met earlier this week, the reconstruction is done to accentuate mammal-like characteristics; there's no guarantee that the sleek-pelted otterish look is accurate.

The reason this comes up is the discovery of a mid-Jurassic docodont whose skeleton shows some remarkably mammal-like features.  This little guy, called Microdocodon (evidently named by someone who believes in keeping things simple and obvious) was around 165 million years ago, which (for reference) is a good hundred million years before the non-avian dinosaurs became history.

Well, prehistory.

What's interesting about Microdocodon is that it had a mammalian hyoid bone -- unique in our skeleton as the only bone that does not articulate with another bone.  It's a horseshoe-shaped bone that connects to the tongue, epiglottis, larynx, and muscles that support the neck, and gives us our ability to chew, swallow, keep an open airway while we're asleep -- and talk.

In non-human mammals, it's all about the first three, and it's thought that the evolution of the hyoid bone was instrumental in improving the range of food mammals could eat, since the ability to chew meant they weren't confined to swallowing big chunks of food at once.

"It is a pristine, beautiful fossil. I was amazed by the exquisite preservation of this tiny fossil at the first sight," said Zhe-Xi Luo, a professor of biology at the University of Chicago and lead author of the study, which appeared in Science last week.  "We got a sense that it was unusual, but we were puzzled about what was unusual about it  After taking detailed photographs and examining the fossil under a microscope, it dawned on us that this Jurassic animal has tiny hyoid bones much like those of modern mammals...  Now we are able for the first time to address how the crucial function for swallowing evolved among early mammals from the fossil record.  The tiny hyoids of Microdocodon are a big milestone for interpreting the evolution of mammalian feeding function."

The most amazing thing about all this is that Microdocodon catches evolutionary remodeling of a pre-existing skeleton right in midstream.  "Hyoids and ear bones are all derivatives of the primordial vertebrate mouth and gill skeleton, with which our earliest fishlike ancestors fed and respired," said Bhart-Anjan Bhullar, postdoctoral scholar at Yale University and co-author of the paper.  "The jointed, mobile hyoid of Microdocodon coexists with an archaic middle ear -- still attached to the lower jaw.  Therefore, the building of the modern mammal entailed serial repurposing of a truly ancient system."

So that's our lens into the past for today, and a look at a group of mammal relatives that until I read this paper, I didn't even know existed.  All of this making me question how anyone can think science is boring.  If after studying and/or teaching science over the past forty years I can still find something new and astonishing, you have to appreciate science's capacity for inducing awe -- and wonder what new discoveries lie ahead.

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The subject of Monday's blog post gave me the idea that this week's Skeptophilia book recommendation should be a classic -- Konrad Lorenz's Man Meets Dog.  This book, written back in 1949, is an analysis of the history and biology of the human/canine relationship, and is a must-read for anyone who owns, or has ever owned, a doggy companion.

Given that it's seventy years old, some of the factual information in Man Meets Dog has been superseded by new research -- especially about the genetic relationships between various dog breeds, and between domestic dogs and other canid species in the wild.  But his behavioral analysis is impeccable, and is written in his typical lucid, humorous style, with plenty of anecdotes that other dog lovers will no doubt relate to.  It's a delightful read!

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

Science shorts

Today, I want to look at some awesome shorts that were too good to pass up.

No, not that kind.

In the last couple of days I found three recent bits of research that are just plain cool, and I couldn't resist sharing them with you.

First, we have a new discovery out of China showing that flowering plants were around a great deal earlier than we'd thought -- the early Jurassic Period, 174 million years ago.  This pushes back the earliest evidence of flowering plants by a good fifty million years!

Called Nanjinganthus dendrostyla, this little flower grew during a time when we'd thought there was nothing much around, botanically speaking, but gymnosperms (relatives of today's spruces, firs, and pines), ferns, and other more primitive plants.  But a fantastically well-preserved group of fossils has shown that they shared the space with some of the earliest angiosperms, or flowering plants.

One of the Nanjinganthus dendrostyla fossils 

After careful microscopic analysis of the flower, the researchers put it together like this:

So cool, even if it's not something you'd necessarily want as the centerpiece of your garden.

The significance of the discovery goes beyond its age.  There are some other features that bear mention, as is described over at the blog In Defense of Plants (linked above):

Another surprising feature is the presence of an inferior ovary that, by its very definition, sits below the sepals and petals.  It has long been hypothesized that early angiosperms would exhibit superior ovaries so this discovery means that we must rethink our expectations of how flowers evolved.  For instance, it suggests we may not be able to make broad inferences on the past based on what we see in extant angiosperm lineages.  It could also suggest that the origin of flowering plants was not a single event but rather a series of individual occurrences.  It could also be the case that the origin of flowering plants occurred much earlier than the Jurassic and that Nanjinganthus represents one of many derived forms.  Only further study and more fossils can help us answer such questions.

The second story comes from zoology, and it concerns eyeless cave fish -- fish whose ancestors were trapped in dark caves, and evolved to lose their visual sense.  There's a fundamental misunderstanding that a lot of people have about these species, usually centering around the Lamarckian view that the fish lost their eyes "because they didn't need them any more."  The actual truth of the matter seems to be that if you're in perpetual darkness, using a lot of your energy to produce and maintain a structure as complex and delicate as the eye would be a waste, and diverting those resources to other, more useful purposes is a significant advantage.  It's a subtle point, but an important one.

In any case, this current research turns on two questions -- how cave fish navigate their habitat, and why they have asymmetrical faces -- a curiosity that they share with blind cave crickets.

It turns out that the two questions are related.  The convex side of the fish's skull contains more neuromasts, organs that are not only tactile sensors but give fish information about vibrations and water speed and direction.  All fish have these, but blind fish rely on them to create a mental map of their habitat.  Researchers found that most of the fish have skulls that bend slightly to the left, meaning they're getting tactile input mostly from the right.  And just as you expect, the fish whose skull bends to the left keep their right side in close contact to the walls, and tend to move counterclockwise around their habitat -- and the right-bending fish move the opposite way!

The whole thing brings to mind an article that appeared many years ago in the inimitable science spoof The Journal of Irreproducible Results, describing a little mammal called the Sidehill Gouger that has two short legs on one side and two long legs on the other, so it can stand upright on hillsides.  Thus, like our cave fish, some Sidehill Gougers always travel clockwise, and others counterclockwise.  The article goes into the genetics of the trait, describing how the offspring of a right and a left-handed Gouger produces some of each, but heterozygous individuals end up with diagonally opposite short legs.

They're called "Rockers."

I doubt there's any analog in the cave fish, but it's interesting and more than a little ironic that a piece from JIR actually ended up within hailing distance of reality.


The last story puts to rest the idea that scientists don't know how to have fun.  A couple of mechanical engineers from Boston University, Alexandros Oratis and James Bird, published some research this week in Physical Review Letters describing the physics of shooting a rubber band -- and how to optimize your strategy so it goes straight and doesn't smack your thumb on the way out.

After filming rubber band shooting with an ultra-high-speed camera, what Oratis and Bird found was that when it comes to tension, less is more.  When the rubber band is released, the release of tension in the band zooms forward, and the back end of the band follows, but at a slower speed.  When the tension release reaches your thumb, it allows your thumb to snap forward, dodging the band as it passes.  If you pull too hard, the speed of the tension release is higher, and it's simply too fast for your thumb to duck out of the way.  The result: you give yourself a nice stinging smack.

Wider rubber bands also work better, and for a similar reason; they have a higher tension, so when that's released, your thumb jerks forward more quickly.

Me, I wonder how many times Oratis and Bird popped each other with rubber bands while doing this research.


So there you have it.  Rubber band war strategy, lopsided cave fish, and extremely early flowers.  All of which illustrate what I've claimed all along: science is fun.

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Carl Zimmer has been a science writer for a long time, and his contributions -- mostly on the topic of evolution -- have been featured in National Geographic, Discover, and The New York Times, not to mention appearances on Fresh Air, This American Life, and Radiolab.  He's the author of this week's Skeptophilia book recommendation, which is about the connections between genetics, behavior, and human evolution -- She Has Her Mother's Laugh: The Powers, Perversions, and Potentials of Heredity.

Zimmer's lucid, eloquent style makes this book accessible to the layperson, and he not only looks at the science of genetics but its impact on society -- such as our current infatuation with personal DNA tests such as the ones offered by 23 & Me and Ancestry.  It's a brilliant read, and one in which you'll learn not only about our deep connection to our ancestry, but where humanity might be headed.

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

A new view of the "eye lizard"

I am forever astonished at the level of detail we can infer from fossils that are hundreds of millions of years old.

The most recent example of this came from analysis of a fossil of Stenopterygius, an ichthyosaur that lived during the Jurassic Period (this particular fossil has been dated to about 180 million years ago).  We usually think of fossils as preserving bones and teeth, and occasionally impressions of scales or skin or feathers -- but this one was so finely preserved that researchers have been able to make some shrewd inferences about color, metabolism, and the structure of soft tissues.

Artist's conception of Stenopterygius [Image licensed under the Creative Commons Nobu Tamura (http://spinops.blogspot.com), Stenopterygius BW, CC BY-SA 3.0]

We've known for a long time that ichthyosaurs are bizarre animals.  They were streamlined predators that look remarkably like dolphins, although they are only distantly related (making the two groups a great example of convergent evolution).  A number of them had an even stranger feature, which is the largest eye-diameter-to-body-size ratio of any animal known -- the well-named Ophthalmosaurus (Greek for "eye lizard") was six meters long and had eyes the size of basketballs.

Stenopterygius was a bit smaller, with an average adult size of four meters.  But up until recently, all we've been able to do is speculate on what it might have looked like, and how it behaved.  A discovery in Germany, described in a paper in Nature called "Soft-Tissue Evidence for Homeothermy and Crypsis in a Jurassic Ichthyosaur" and authored by no fewer than 23 scientists, has given us incredibly detailed information on these oddball dinosaurs.

The authors write:

Ichthyosaurs are extinct marine reptiles that display a notable external similarity to modern toothed whales.  Here we show that this resemblance is more than skin deep.  We apply a multidisciplinary experimental approach to characterize the cellular and molecular composition of integumental tissues in an exceptionally preserved specimen of the Early Jurassic ichthyosaur Stenopterygius.  Our analyses recovered still-flexible remnants of the original scaleless skin, which comprises morphologically distinct epidermal and dermal layers.  These are underlain by insulating blubber that would have augmented streamlining, buoyancy and homeothermy.  Additionally, we identify endogenous proteinaceous and lipid constituents, together with keratinocytes and branched melanophores that contain eumelanin pigment.  Distributional variation of melanophores across the body suggests countershading, possibly enhanced by physiological adjustments of colour to enable photoprotection, concealment and/or thermoregulation.  Convergence of ichthyosaurs with extant marine amniotes thus extends to the ultrastructural and molecular levels, reflecting the omnipresent constraints of their shared adaptation to pelagic life.

So from a 180-million-year-old fossil, we now know that Stenopterygius (1) was a homeotherm (colloquially called "warm-blooded"), (2) had a blubber layer much like modern dolphins and whales, and (3) were countershaded -- dark on top and light underneath, to aid camouflage -- similar to dozens of species of modern fish.

This level of preservation is extremely unusual.  "Both the contour of the body and the remains of internal organs are clearly visible," said paleontologist Johan Lindgren of the University of Lund, who co-authored the paper.  "Surprisingly, the fossil is so well preserved that it is possible to observe individual cell layers inside the skin."

"This is the first direct chemical evidence of warm blood in an ichthyosaur, because a subcutaneous fat layer is a characteristic of warm-blooded animals," said Mary Schweitzer of North Carolina State University, also a co-author.  "Ichthyosaurs are interesting because they have many features in common with dolphins, but they are not related at all to these mammals that inhabit the sea.  But the enigma does not stop there...  They have many characteristics in common with living marine reptiles, such as sea turtles; but we know from the fossil record that they gave live birth to their young...  This study reveals some of those biological mysteries."

Which is pretty astonishing.  I've always had a fascination for the prehistoric world, and have spent more time than I like to admit wondering what it might have been like to live in the Jurassic world.  This research gives us one more piece of information -- about a fierce prehistoric predator that shared some amazing similarities to creatures that still swim in our oceans.

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One of the best books I've read recently is Alan Weisman's The World Without Us.  I wouldn't say it's cheerful, however.  But what Weisman does is to look at what would happen if the human race was to disappear -- how long it would take for our creations to break down, for nature to reassert itself, for the damage we've done to be healed.

The book is full of eye-openers.  First, his prediction is that within 24 hours of the power going out, the New York Subways would fill with water -- once the pumps go out, they'd become underwater caves.  Not long thereafter, the water would eat away at the underpinnings of the roads, and roads would start caving in, before long returning Manhattan to what it was before the Europeans arrived, a swampy island crisscrossed by rivers.  Farms, including the huge industrial farms of the Midwest, would be equally quick; cultivated varieties of wheat and corn would, Weisman says, last only three or four years before being replaced by hardier species, and the land would gradually return to nature (albeit changed by the introduction of highly competitive exotic species that were introduced by us, accidentally or deliberately).

Other places, however, would not rebound quickly.  Or ever.  Nuclear reactor sites would become uninhabitable for enough time that they might as well be considered a permanent loss.  Sites contaminated by heavy metals and non-biodegradable poisons (like dioxins) also would be, although with these there's the possibility of organisms evolving to tolerate, or even break down, the toxins.  (No such hope with radioactivity, unfortunately.)

But despite the dark parts it's a good read, and puts into perspective the effect we've had on the Earth -- and makes even more urgent the case that we need to put the brakes on environmental damage before something really does take our species out for good.