Mammals of unusual size

When we've gone to the Museum of Natural History in Washington, D.C., I always gravitate toward the prehistoric animals.

I guess that's understandable enough, given that I made my career as a biology teacher.  Judging by the crowds, I'm not alone.  However, unlike most folks -- who seem especially taken by dinosaurs like T. rex and triceratops -- I always head toward the prehistoric mammals.

I love to picture what "endless forms most beautiful and most wonderful" (to pilfer a phrase from Darwin's Origin of Species) crawled, ran, jumped, scampered, and thundered across the planet long before we ever showed up on the scene.  Mammals have been around for a long time, a lot longer than you might think if you learned that "mammals arose once the dinosaurs were extinct" in grade school.  The first certain mammal fossils date from the late Triassic, about 225 million years ago, so at that point the non-avian dinosaurs still had around 160 million years to enjoy their hegemony before the double-whammy of the Chicxulub Meteorite Impact and the eruption of the Deccan Traps in India wiped them out.

The mammals were small for a while, of course.  Prior to the Cretaceous extinction, most of them fell into one of three groups; multituberculates (which looked superficially like rodents, but were only distantly related), eutriconodonts (a bit weasel-like, but again, not related), and spalacotheriids (something like a modern mole, but once again...).  None left any living descendants, and the biggest ones were the size of a small dog.

Understandable that they did what they could not to be noticed when there were loads of hungry dinosaurs around.

It's true that once the non-avian dinosaurs were wiped out, there was significant evolutionary pressure to diversify and get larger, to take advantage of the niches emptied by the mass extinction.  And one of the groups that got big fast were the brontotheres -- Greek for "thunder beasts."

They, like other mammal groups, started small.  They're perissodactyls -- the "odd-toed ungulates," a group that contains modern horses, rhinos, and tapirs.  And although they looked superficially like rhinos, their teeth show a closer relationship to horses.  One of the classic brontotheres is the slingshot-horned Megacerops (formerly named Brontops):

[Image licensed under the Creative Commons Creator:Dmitry Bogdanov, Megacerops-coloradensis, CC BY 3.0]

The reason this comes up is a paper last week in Science, which I found about from my author friend (and frequent contributor to Skeptophilia) Andrew Butters, in which a team from the University of Alcalá in Madrid used patterns of evolution in brontotheres to investigate Cope's rule -- that in the absence of other factors, larger individuals have a higher survival rate, and species evolve to get larger over time.

The results certainly seem to hold here.  The survival rate of brontothere species during the Eocene Epoch, from 55 to 34 million years ago -- their heyday -- is directly proportional to their size.  However, one corollary to Cope's rule is that when conditions suddenly change, large species are less able to respond flexibly, and are more prone to extinction.  Which is exactly what happened at the end of the Eocene; by the beginning of the next epoch, the Oligocene, the brontotheres were gone.

It was hardly the end of the large mammals, however.  Another perissodactyl group, the rhinos and their relatives, stepped in to fill the empty niches, and this led to the largest terrestrial land mammal known, Paraceratherium (formerly called Baluchitherium and Indricotherium).

[Image licensed under the Creative Commons Dmitry Bogdanov creator QS:P170,Q39957193, Indricotherium11, CC BY 3.0]

Standing next to Paraceratherium, you'd have come up to his kneecap.

If that's not scary enough, the Oligocene also saw mammals like the enormous Daenodon -- the name means "terrible teeth" -- which looked a bit like a pig on stilts:

[Image licensed under the Creative Commons Max Bellomio, Daeodon shoshonensis , CC BY-SA 4.0]

Oh, and there were also phorusrhacids stomping around the place.  Colloquially known as "terror birds."  Think of an enormous carnivorous ostrich on steroids, and you have the idea.

So yeah.  Even though I love hanging around in the prehistoric mammal part of the Museum of Natural History, it would be another thing entirely to go back there and actually try to survive.  An Eocene Park or Oligocene Park would be just as terrifying as a Jurassic Park.

Nature is red in tooth and claw, and all that sort of stuff.  Guess it always has been.

In any case, it does make me glad that the scariest thing I have to deal with around here are squirrels, raccoons, and the occasional coyote.  I'll take those over "thunder beasts," "terrible teeth," and "terror birds" any day.

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Mammals down under

Sometimes all it takes is one new discovery to send scientists back to the drawing board.

Of course, as astrophysicist Neil deGrasse Tyson correctly points out, scientists are always at the drawing board, or should be.  "If you're not at the drawing board," he says, "you're not doing science."  But still, it does seem sometimes like things are pretty well figured out, and then...

... boom.

There was a "boom" moment in the field of mammalian evolution this week, delivered by a paper in the journal Alcheringa: The Australasian Journal of Palaeontology.  The authors -- led by the brilliant paleontologist and polymath Timothy Flannery, of the University of Melbourne -- describe a fossil find that would seemingly be of interest only to people fascinated by minutiae of paleontology; a jawbone of a tribosphene, a proto-mammal with distinctive triangular, three-pointed molars, from the early Jurassic Period in Australia.

The problem is, it kind of shouldn't have been there.  Tribosphenes, which are in a group that is ancestral to both marsupial and placental mammals, were thought to originate in Laurasia, the northern half of the (at that point, split) supercontinent Pangaea.  (Laurasia comprised land that is now found in North America, Europe, and Asia.)  Australia, on the other hand was part of the southern half of Pangaea, called Gondwana, along with Africa, Antarctica, and South America.

This origin for the tribosphenes was considered so certain that they used to be called boreosphenes -- from the Greek word Βορέας, which was the name of the god of the north wind.

Guess it's a good thing they changed the name.

Eomaia, an early tribosphene mammal from China [Image licensed under the Creative Commons Nobu Tamura (http://spinops.blogspot.com), Eomaia NT, CC BY-SA 3.0]

There's no doubt that there were tribosphenes in Laurasia, too; one of the earliest, Tribactonodon, can be found in the Lower Cretaceous Durlston Formation in England.  (Others have been found in Mongolia and in Portugal.)  The idea was that they started in Laurasia and only later spread southward to Gondwana -- so Australia's iconic marsupials originally started out much farther north.

The discovery of a tribosphene in Australia sixty million years earlier than that indicates that some rethinking may be in order.

"I was re-analyzing these fossils that turned up in Victoria from the age of dinosaurs," Flannery said, in an interview with Australian Geographic.  "And then I started looking more widely for similar sorts of fossils found elsewhere and it turned out all of them were in the southern hemisphere and all are Jurassic or Cretaceous in age [from 199–66 million years ago]...  And we realized the thing that unites all these Southern Hemisphere fossils is they have these very strange, complicated molars that let the animals puncture shear and crush, all at the same time, what they were eating.  I resisted the conclusion as long as I could, but the evidence is compelling.  These shrew-like animals from Australian are actually the ancestors of both the earliest placentals and the earliest marsupials."

"We’ve been able to show that the relevant fossils that look like they are anatomically likely to be close to the common ancestor of marsupials and placentals are found exclusively in the southern continents and are from an older time period than the oldest mammal similar fossils seen the north," said Kristofer Helgen, who co-authored the paper.  "And that indicates these groups of mammals had their ancestry in the southern continents at an earlier time period and then later colonized the northern continents.  It absolutely turns our previous understanding on its head."

Which is tremendously exciting.  Far from being frustrated by stuff like this, these are the moments scientists live for -- when they find out that our previous understanding is incomplete, skewed, or flat wrong.  That's when the real process of discovery happens, and often when we gain a lens on a bit of the universe we weren't seeing clearly.

It's why I get so profoundly frustrated with the ridiculous attitude, "why study science?  It could all be proven wrong tomorrow."  To me, that's a completely backwards way of looking at it.  The truth is that science, unlike just about every other path to knowledge humans have ever utilized, has the ability to self correct.  When scientists find out a bit of our understanding is wrong, they neither throw their hands up in despair, nor do they double down on the error; they take steps to fix it.

And isn't that better than remaining in a state of error, incomprehension, or ignorance?

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Redefining the primitive

One of the most interesting, and persistent, misconceptions about evolutionary biology revolves around the use of the word "primitive" to describe certain life forms.

The misunderstanding goes back to Aristotle, really.  The great philosopher proposed a concept usually known by its Latin name of scala naturae, the "scale of nature."  Often called "the great chain of being."  The idea is that life has progressed up some sort of ladder of complexity, starting with something like bacteria, then upwards through jellyfish and worms and bugs and fish and amphibians and reptiles and "lower" mammals, finally arriving at us, who (of course) being the pinnacle of creation, stand proudly at the top of the ladder.

The problem with this, as with many misconceptions, is that in some ways it's kinda sorta almost true.  Something like today's bacteria were the first life forms, and the progression of fish > amphibian > reptile > mammal is pretty well established.  The problems start when you look at life forms earlier than fish; during the famous Cambrian Explosion, most of the phyla of animals branched off and diversified in a relative flash, not only including the ones we have around today but a number of oddball groups that didn't survive.  So with respect to most modern groups of species, that smooth progression up the ladder didn't actually happen.

The problem gets worse when you try to apply the word "primitive" to current life forms.  Is a bug more primitive than a human?  Both are alive right now; each of them has exactly the same length of ancestral history.  It doesn't even work if you link "primitiveness" with "complexity."  Humans and bugs are both complex organisms, they're just complex in different ways.  Certainly, there's a difference in intelligence; most humans are smarter than most bugs.  But intelligence doesn't equal evolutionary success.  By just about any measure, insects are by far the most successful animals on the Earth.

It recalls the famous anecdote about the illustrious biologist J. B. S. Haldane.  Haldane was a zoologist but also rather notorious as an outspoken atheist, and religious people used to go to his talks to heckle him about it.  At one, during the question-and-answer period, a woman asked, "Professor Haldane, what have your studies in biology told you about the nature of God?"

Haldane thought for a moment, and finally said, "All I can say, ma'am, is that he must have an inordinate fondness for beetles."

In any case, you have to be extraordinarily careful how you apply the word "primitive."  In biology it's now used to describe traits (not entire organisms), with a very specific, restricted meaning, defined as "a trait that is shared with the ancestral form."  An example is the vascular tissue -- the internal plumbing -- in plants, which is "advanced" as compared to the trait of "lacking vascular tissue."  Vascular plants evolved from non-vascular ones, so apropos of that trait, mosses (which lack vascular tissue) are primitive as compared to ferns (which have vascular tissue). 

But it still requires caution, because it's all too easy to assume that "primitive traits are less complex" or (worse) that "if an organism is like humans, that means it's advanced," neither of which are true.  For example, take a look at the paper last week in The American Naturalist written by a team from the University of Washington that questions the notion of primitiveness with respect to something most of us take for granted -- reproduction in mammals.

There are three basic modes of reproduction in Class Mammalia.  A couple of modern species are oviparous -- egg-laying (the monotremes, namely the echidna and the platypus).  Another group are marsupials, which give birth to extremely altricial (undeveloped) young, because the mothers have no placentas to interface between themselves and their babies.  Once the offspring are too big (which isn't very big at all; kangaroos are about two centimeters long at birth) they are born, and develop the rest of the way in the mother's pouch.  The third are the placentals such as ourselves (and every mammal you've ever heard of other than the monotremes and marsupials).

Egg-laying certainly is a primitive trait; it's pretty clear that the reptilian ancestors of the earliest mammals were oviparous.  But what about the presence of a placenta?  Once again, the danger is in assuming that it's the "advanced trait" because (1) humans are placentals, (2) there are currently more placentals than marsupials, and (3) somehow the placental method "seems more complicated."  These are all more like smug self-congratulation than they are science, and none are reliable indicators of the primitiveness of a trait.

The current study, in fact, suggests that the placental mode of reproduction may predate the marsupial method -- by a lot.  The researchers studied the odd multituberculates, a group of mammals that were amongst the first to diversify significantly, way back in the Jurassic Period around 170 million years ago.  They were some of the most common mammals for a very long time, finally going extinct about 35 million years ago (for reasons unknown). 

The multituberculate Sunnyodon notleyi [Image licensed under the Creative Commons FunkMonk (Michael B. H.), Sunnyodon, CC BY-SA 3.0]

The salient point here is that the marsupial mammals, including the extinct ones that have been studied, have a very distinctive pattern of bone growth that is connected to their being born so incredibly undeveloped.  A careful analysis of multituberculate bones shows they're a great deal more similar to today's placentals -- despite the fact that they branched off from the rest of Class Mammalia way earlier than the marsupials did.

So it looks like the little multituberculates had placentas and long gestation periods, and our mode of reproduction is actually the primitive one.  Meaning the marsupial lineage lost the ability to form a placenta, rather than our lineage gaining it.  Why that happened isn't known; but as we've seen, a trait doesn't need to be complex to give its owner a selective advantage.  Perhaps in marsupials, the draw on the mother's resources is lowered enough by giving birth early that it allows her a better shot at surviving -- but that's pure speculation.

Whatever it is, both modes function perfectly well.  "Evolution," as biologist Richard Dawkins put it, "is the law of 'whatever works.'"

And it all reinforces the notion that there is no "great chain of being," there's just an enormous tangled web of which we are just a single strand. 

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The origin of venom

We're all aware of animals with venomous bites -- most of the familiar ones being either snakes or spiders.  It's an interesting topic, but before we begin, let's get our definitions straight, as summed up in this online conversation that has since gone viral (deservedly):

There are a lot of animals that are venomous which are neither snakes nor spiders, however.  There are mollusks like the blue-ringed octopus and the deadly cone snails of the south Pacific, many jellyfish (including the phenomenally venomous box jellies, most common in the waters off the east coast of Australia), scorpions, a few lizards (like the gila monster), and even mammals like the bizarre solenodons, which look like scaled-down versions of the Rodents Of Unusual Size from The Princess Bride.

[Image licensed under the Creative Commons Seb az86556, Hispaniolan Solenodon crop, CC BY-SA 3.0]

In fact, it's the mammalian venomous animals, including not only solenodons but various shrews and the oddball primate called the slow loris, that bring the topic up today.  A paper appeared last week in BMC Biology, about some research out of the University of Okinawa supporting the startling conclusion that the noxious proteins in the saliva of venomous mammals are structurally related to the proteins that serve the same function in hemotoxic snakes like rattlesnakes, vipers, and adders.

On first glance, this may not seem that odd, but consider what it means.  Saying the venom proteins have the same function is not the same as saying they have the same structure.  If the proteins have the same structure, it means that the genes that produced them do as well.  And if that's the case, chances are, those genes share a common ancestor -- and then descended (albeit with modifications) through the ensuing three hundred million years since the lineages that led to today's venomous snakes and mammals split.

Venoms in these animals are complex mixtures of chemicals, but both rattlesnakes and solenodons (for example) have venom containing a class of complex proteins called kallikrein serine proteases.  These are protein-degrading enzymes that in many animals have a function in regulating blood pressure -- accounting for the localized tissue breakdown and drop in blood pressure you see in the victim of a rattlesnake bite.

What's curious -- and what touched off this particular piece of research -- is that all mammals, ourselves included, have small amounts of kallikrein serine proteases in the saliva.  In us (and, in fact, in most mammals), they seem to serve no purpose -- they appear to be vestigial remnants from our ancestry.  But in the lineages that led to both venomous snakes and venomous mammals, they increased in concentration until they could be used, injected into a bite, to subdue and digest prey.

"In [last week's] paper, we hypothesized that in the ancestor of snakes and mammals, there was a common group of genes that had a toxic potential," said Agneesh Barua, who was the co-lead-author along with Ivan Koladurov.  "Snakes and mammals then took different evolutionary paths, with snake lineages evolving diverse and increasingly toxic concoctions, while in mammals, venom did evolve, but to a much lesser degree.  But what we wanted to know is whether the toxins within mammal and snake venom evolved from a common ancestral gene...  There are so many different serine proteases that have a high degree of similarity, that until now, it was too difficult to isolate the right genes needed to determine the evolutionary history.  [Our results are] really strong evidence for our hypothesis that venom evolved from a common group of genes in an ancestor that had a toxic potential.  But the most surprising thing was that non-toxic salivary kallikreins, like those found in humans and mice, also evolved from the same ancestral gene."

Yet another nail in the coffin of creationism, if you needed one.

What I find coolest about this is that it's a reminder of the unity of our biodiversity here on Earth -- that the tapestry of life was produced from threads with a common source, a couple of billion years ago.  And, best of all, that in looking at today's organisms, we can still see remnants of that common origin, even in pairs of species that look nothing alike.

I'll end with the prescient quote attributed to Chief Seattle, that seems more apt today given our knowledge from science than it did when he wrote it in 1854: 

This we know: the Earth does not belong to man, man belongs to the Earth.  All things are connected like the blood that unites us all.  Humankind has not woven the web of life.  We are but one strand within it.  Whatever we do to the web, we do to ourselves.  All things are bound together; all things connect.

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One of my favorite writers is the inimitable Mary Roach, who has blended her insatiable curiosity, her knowledge of science, and her wonderfully irreverent sense of humor into books like Stiff (about death), Bonk (about sex), Spook (about beliefs in the afterlife), and Packing for Mars (about what we'd need to prepare for if we made a long space journey and/or tried to colonize another planet).  Her most recent book, Fuzz: When Nature Breaks the Law, is another brilliant look at a feature of humanity's place in the natural world -- this time, what happens when humans and other species come into conflict.

Roach looks at how we deal with garbage-raiding bears, moose wandering the roads, voracious gulls and rats, and the potentially dangerous troops of monkeys that regularly run into humans in many places in the tropics -- and how, even with our superior brains, we often find ourselves on the losing end of the battle.

Mary Roach's style makes for wonderfully fun reading, and this is no exception.  If you're interested in our role in the natural world, love to find out more about animals, or just want a good laugh -- put Fuzz on your to-read list.  You won't be disappointed.

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

Megarhino

Yesterday, we dealt with how freaking huge the universe is.  Today, we're going to look at something that, on its own scale, is also freaking huge.  

Paleontologists working at a site in the Linxia Basin, in Gansu Province in northwestern China, found a skull and spine of what appears to be the largest land mammal that ever walked the Earth.  Called Paraceratherium, this thing was distantly related to modern rhinos, something that is apparent from the artist's reconstructions of what it may have looked like, except for being (1) hornless and (2) absolutely enormous, even by rhinocerosian standards.

Paraceratherium stood five meters tall at the shoulder.  That means if you took a typical twelve-foot extension ladder and propped it against one (Caution!  Do Not Try This At Home!), climbed to the top and reached as high as you could, you'd maybe be able to pat it on the back.  Its head was about seven meters off the ground, and it was on the order of eight meters long from nose to butt.

It's estimated to have weighed 24 tons, which for reference, is about as much as six full-grown African elephants.

Indricotherium, one of Paraceratherium's slightly smaller cousins [Image licensed under the Creative Commons Creator:Dmitry Bogdanov, Indricotherium11, CC BY 3.0]

I don't know about you, but to me that is staggering.  Think of how much energy that thing used just to walk.  Think of the booming sounds it made when it set its feet down.  Think of how loud the vocalizations of that thing could have been.

Also, think about the piles of dung it must have left around.  "It's your turn to pooper-scoop the Paraceratherium" must have been a devastating thing to hear, back then.

Fortunately, there were no humans around to worry about such matters.  Paraceratherium lived during the Oligocene Epoch (between 34 and 25 million years ago), a time when a lot of groups of mammals got really large -- no one knows why, although there does seem to be a tendency for selection toward large body size when the climate is clement and there's plenty of food.  Also, this was the peak of recovery from the devastating Paleocene-Eocene Thermal Maximum, a climatic spike that had occurred about twenty million years earlier and which coincided with worldwide oceanic anoxia and widespread extinctions, so there was very high biodiversity, and probably equally high competition between species in similar niches.

In any case, that's the current holder of the "Largest Land Mammal Ever" award.  Given how stupendous they must have looked, it's sad they became extinct, although maybe it's just as well.  Imagine what it'd be like with these behemoths stomping around.  We have enough problems keeping deer out of our vegetable garden, I don't even want to think about how we'd keep out a Paraceratherium looking for a quick snack.

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One of the most devastating psychological diagnoses is schizophrenia.  United by the common characteristic of "loss of touch with reality," this phrase belies how horrible the various kinds of schizophrenia are, both for the sufferers and their families.  Immersed in a pseudo-reality where the voices, hallucinations, and perceptions created by their minds seem as vivid as the actual reality around them, schizophrenics live in a terrifying world where they literally can't tell their own imaginings from what they're really seeing and hearing.

The origins of schizophrenia are still poorly understood, and largely because of a lack of knowledge of its causes, treatment and prognosis are iffy at best.  But much of what we know about this horrible disorder comes from families where it seems to be common -- where, apparently, there is a genetic predisposition for the psychosis that is schizophrenia's most frightening characteristic.

One of the first studies of this kind was of the Galvin family of Colorado, who had ten children born between 1945 and 1965 of whom six eventually were diagnosed as schizophrenic.  This tragic situation is the subject of the riveting book Hidden Valley Road: Inside the Mind of an American Family, by Robert Kolker.  Kolker looks at the study done by the National Institute of Health of the Galvin family, which provided the first insight into the genetic basis of schizophrenia, but along the way gives us a touching and compassionate view of a family devastated by this mysterious disease.  It's brilliant reading, and leaves you with a greater understanding of the impact of psychiatric illness -- and hope for a future where this diagnosis has better options for treatment.

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

 

Monster mash-up

Today we're going to turn our attention once more to the distant past, for three stories about three very strange extinct animals.

The first one springboards off Monday's post, about the spectacular Kem Kem fossil beds in Morocco, that gives us a snapshot of "the most dangerous place in the history of planet Earth," according to Nizar Ibrahim of the University of Detroit, who led the team that investigated the site.

What we already knew was impressive enough, with scads of gigantic predators with Big Nasty Pointy Teeth coming at you from all directions, including overhead.  But a paper this week in Nature added another dimension to one of the Kem Kem species -- Spinosaurus, a thirteen-meter-long, eighteen-ton dinosaur with a giant sail running down its back and a row of evil-looking conical six-centimeter-long teeth.

Thus far, it sounds like another lumbering predator of the kind made famous by Jurassic Park, but now Nizar Ibrahim is lead author on another study, called "Tail-Propelled Aquatic Locomotion in a Theropod Dinosaur," we find out something that makes it even more terrifying:

This thing was aquatic.

So we're talking about a water-dwelling predator that makes great white sharks look like goldfish.

[Image licensed under the Creative Commons Mariomassone, Spinosaurus white background 2, CC BY-SA 3.0]

The authors write:

This dinosaur has a tail with an unexpected and unique shape that consists of extremely tall neural spines and elongate chevrons, which forms a large, flexible fin-like organ capable of extensive lateral excursion.  Using a robotic flapping apparatus to measure undulatory forces in physical models of different tail shapes, we show that the tail shape of Spinosaurus produces greater thrust and efficiency in water than the tail shapes of terrestrial dinosaurs and that these measures of performance are more comparable to those of extant aquatic vertebrates that use vertically expanded tails to generate forward propulsion while swimming.  These results are consistent with the suite of adaptations for an aquatic lifestyle and piscivorous diet that have previously been documented for Spinosaurus.  Although developed to a lesser degree, aquatic adaptations are also found in other members of the spinosaurid clade, which had a near-global distribution and a stratigraphic range of more than 50 million years, pointing to a substantial invasion of aquatic environments by dinosaurs.

So this gives new meaning to the tagline from Jaws, "Don't go into the water."

Then from Madagascar we have a well-preserved fossil from the weird -- and poorly-known -- group called gondwanatheres.  These were mammals, mostly confined to the Southern Hemisphere (unsurprising given the name, if you know your prehistoric geography), and despite a superficial similarity to a capybara, aren't closely related to any current mammalian group.

[Artist's reconstruction of the gondwanathere Vintana sertichi [Image licensed under the Creative Commons Nobu Tamura email:nobu.tamura@yahoo.com http://spinops.blogspot.com/, Vintana NT small, CC BY-SA 4.0]

The most recent find is from the species Adalatherium hui, which is a Greek/Malagasy mishmash meaning, basically, "crazy beast."  The species predated the Cretaceous Extinction -- so it coexisted with the last of the non-avian dinosaurs -- and had a number of bizarre features, such as a hole in the top of the snout.  The oddity of its features may have to do with isolation in an island environment, allowing the evolution of the species to run in a different direction from its mainland relatives.  "Island environments promote evolutionary trajectories among mammals and other vertebrates that contrast with those on continents, and which result in demonstrable anatomical, physiological and behavioural differences," write the authors, a team led by David Krause of the Denver Museum of Nature and Science.  "These differences have previously been ascribed to markedly distinct selection regimes that involve factors such as limited resources, reduced interspecific competition and a paucity of predators and parasites."

So here's a reconstruction of Adalatherium.  The badger-like coloration is artistic license, of course, based on the inference from its skeleton that it made its living by digging:

[Image courtesy of Andrey Atuchin]

The gondwanatheres seem to be closely related to another weird extinct mammalian group, the multituberculates, about which I wrote a year ago.  Both vanished, for reasons unknown, in the Miocene Epoch, on the order of fifteen million years ago.

The latest piece of research is about the strangest, most alien-looking animal ever, Tullimonstrum (the "Tully Monster," named after Francis Tully, who discovered the first fossils of the species).  If you think I'm being hyperbolic, here's what the Tully Monster looked like:

[Image licensed under the Creative Commons PaleoEquii, Tullimonstrum, CC BY-SA 4.0]

The thing was so peculiar that paleontologists couldn't even decide if it was an invertebrate or a proto-vertebrate; the evidence seemed to favor the latter, and a 2016 study concluded it was an ancestral vertebrate related to lampreys and hagfish based upon its eye structure, fins, and teeth.  But now, new research that included detailed analysis of the eyes using a particle accelerator to determine the elemental makeup of the remnants in the fossil has thrown a wrench into that explanation.  In an article in LiveScience, paleontologist Chris Rogers of the University College-Cork tells us that the ratio of zinc to copper in the animal's eyes is much more like an invertebrate than a vertebrate -- but before we rewrite all the textbooks on Precambrian animals, the distribution of copper wasn't much like an invertebrate, either.  "We... found that Tully's eyes contain different type of copper to that found in vertebrate eyes," Rogers writes.  "But the copper also wasn't identical to that in the invertebrates we studied.  So while our work adds weight to the idea that Tully is not a vertebrate, it doesn't clearly identify it as an invertebrate either."

So we're back to the "what the hell is it?" stage of things.

Anyhow, that's our excursion into the past for today.  As I've pointed out before, the inherently fragmentary nature of the fossil record means that our picture of what life was like back then is going to be incomplete at best.  But slowly, painstakingly, researchers are refining our view of the animal life of eons long gone -- and what they're showing us is strange indeed.

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This week's Skeptophilia book recommendation is an important read for any of you who, like me, (1) like running, cycling, and weight lifting, and (2) have had repeated injuries.

Christie Aschwanden's new book Good to Go: What the Athlete in All of Us Can Learn from the Strange Science of Recovery goes through all the recommendations -- good and bad, sensible and bizarre -- that world-class athletes have made to help us less-elite types recover from the injuries we incur.  As you might expect, some of them work, and some of them are worse than useless -- and Aschwanden will help you to sort the wheat from the chaff.

The fun part of this is that Aschwanden not only looked at the serious scientific research, she tried some of these "cures" on herself.  You'll find out the results, described in detail brought to life by her lucid writing, and maybe it'll help you find some good ways of handling your own aches and pains -- and avoid the ones that are worthless.

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

All ears

One of the coolest things about evolution is how structures get repurposed -- a process that results in numerous examples of homologous structures (similar in structure, different in function), the best-known of which is the wing of a bat, the paw of a cat, the flipper of a whale, and the hand of a human.  Each of these, as every student in an introductory biology class knows, contains 29 bones -- a humerus in the upper part, a radius and an ulna in the lower part, seven carpal bones, five metacarpals, and fourteen phalanges.  The differences are in the sizes and shapes of each, and the distribution of soft tissue around them, adapting each to its specific purpose.

A little hard to explain that if you don't believe there's common ancestry.

That example shows up in just about every biology textbook ever written, but there are scads of others, including homology at the molecular level.  A phenomenal discovery over thirty years ago shows that the proteins that make up the lens of the vertebrate eye -- the alpha-crystallins -- are related to a family of proteins called heat-shock proteins that protect our tissues from stress of various kinds, including temperature fluctuations.  Apparently some time in a collective ancestor, the gene coding for a heat-shock protein acquired a mutation that gave it a new property -- transparency.  Once that happened, it took evolution off in a completely new direction, a phenomenon that has been observed often enough that there's a name for it (three, actually; preaptation, preadaptation, and exaptation).

One long-theorized example of both homologous structures and preaptation is the collection of three little bones in our middle ear -- the malleus (hammer), incus (anvil), and stipes (stirrup).  They act as sound-conducting devices, the vibrations being passed from the eardrum to the little bones, where they resonate at the same frequency and transfer those sound waves into the organ of hearing, the snail-shell-shaped cochlea.  They're pretty critical; a friend of mine had a congenital defect in those bones, where as she got older the hammer progressively tilted away from the anvil, and the loss of contact was gradually robbing her of her hearing.  Amazingly enough, microsurgery on this tiny (eight-millimeter-long) bone was able to correct the defect and restore 90% of her hearing, a testimony to the phenomenal advances medical science has made in the last decades.

Their position and shape clued in evolutionary biologists that as odd as it sounds, the three bones in the middle ear of a human are homologous to three much larger bones in the jaw of a reptile.  You might imagine that given the delicate nature of these structures and the general paucity of fossils, it'd be difficult to find intermediate points in the lineage that showed the transition -- and indeed, that "missing link" (much as I hate that term) was absent for years.

Not any more.

Just this week, a paper came out in Science called, "Integrated Hearing and Chewing Modules Decoupled in a Cretaceous Stem Therian Mammal," by Fangyuan Mao, Yaoming Hu, Chuankui Li,  and Yuanqing Wang (of the Chinese Academy of Sciences), and Morgan Hill Chase, Andrew K. Smith, and Jin Meng (of the American Museum of Natural History).  It describes a little shrew-like early mammal called Origolestes lii, which lived in what is now China between 133 and 120 million years ago.  This places it in the early Cretaceous Period, contemporaneous with a huge variety of dinosaurs (although still a good bit earlier than the Cretaceous usual suspects such as Triceratops and Tyrannosaurus rex).

The phenomenal degree of preservation of this little mammal allowed scientists to study the fine structure of the middle ear bones, and they found exactly what had been theorized -- that the three little bones in our ears had unhooked themselves from the jaw joint, moved, and gotten smaller, and Origolestes was right in the middle of that transition.  The authors write:

The auditory bones, including the surangular [a bone found in the jaws of all vertebrates except mammals, homologous to our malleus bone], have no bone contact with the ossified Meckel’s cartilage; the latter is loosely lodged on the medial rear of the dentary.  This configuration probably represents the initial morphological stage of the definitive mammalian middle ear.  Evidence shows that hearing and chewing apparatuses have evolved in a modular fashion.  Starting as an integrated complex in non-mammaliaform cynodonts, the two modules, regulated by similar developmental and genetic mechanisms, eventually decoupled during the evolution of mammals, allowing further improvement for more efficient hearing and mastication.

So that's pretty spectacular.

Once again, evolution wins the day, not that there should be any doubt at all left.  The evidence for the evolutionary model is abundant even if you discount the fossils entirely, but this kind of thing is just the icing on the cake, similar to the missing intermediate forms between land mammals and whales, which were found -- precisely as predicted -- in an amazing fossil bed in Pakistan in 1994.

Astonishing as it may seem, evolution rarely produces completely novel structures; it molds and repurposes what's already there for new functions.  The tired old canard of finding an automobile in the middle of a field implying a manufacturer is woefully far off the mark; a closer analogy would be taking a car, and gradually modifying it part by part so that each change confers an advantage (or at least confers no disadvantage), and over millions of little transitions, ending up with a Boeing 747.

I'll end with the most direct statement on this topic ever made, a statement wholly supported by little Origolestes with its not-quite-jaws, not-quite-ears, from twentieth-century biologist Theodosius Dobzhansky:

"Nothing in biology makes sense except in the light of evolution."

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Long-time readers of Skeptophilia have probably read enough of my rants about creationism and the other flavors of evolution-denial that they're sick unto death of the subject, but if you're up for one more excursion into this, I have a book that is a must-read.

British evolutionary biologist Richard Dawkins has made a name for himself both as an outspoken atheist and as a champion for the evolutionary model, and it is in this latter capacity that he wrote the brilliant The Greatest Show on Earth.  Here, he presents the evidence for evolution in lucid prose easily accessible to the layperson, and one by one demolishes the "arguments" (if you can dignify them by that name) that you find in places like the infamous Answers in Genesis.

If you're someone who wants more ammunition for your own defense of the topic, or you want to find out why the scientists believe all that stuff about natural selection, or you're a creationist yourself and (to your credit) want to find out what the other side is saying, this book is about the best introduction to the logic of the evolutionary model I've ever read.  My focus in biology was evolution and population genetics, so you'd think all this stuff would be old hat to me, but I found something new to savor on virtually every page.  I cannot recommend this book highly enough!

[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!]

Myths, mammals, and extinctions

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

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

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

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

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

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

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

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

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

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

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

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

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

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