After 'while, crocodile

Because I have an endless fascination for things that are big and powerful and can kill you, today's topic is: Deinosuchus.

If you know a little Greek, the name itself should put you on notice.  It comes from the words δεινός (terror) and σοῦχος (crocodile).  Because crocodiles aren't terrifying enough on their own, apparently.  The largest extant crocodilian is the Australian saltwater crocodile, which can get to be about six meters in length and can weigh twelve hundred kilograms.  It regularly attacks humans, often stupid ones who don't know enough to stay away from the shallow water habitats it prefers, and as the Wikipedia article puts it, "As a result of its power, intimidating size and speed, survival of a direct predatory attack is unlikely if the crocodile is able to make direct contact."

Deinosuchus was just shy of twice as long.  Considering that the usual rule that the mass of an animal varies as the cube of its length, this would put the biggest ones at eight times heavier than a saltie -- something on the order of nine thousand kilograms.

That's equivalent to the mass of a school bus.  Just for reference.

If that's not bad enough, it had teeth up to a foot long.  Lots of them.  The largest species, Deinosuchus riograndensis, which lived (unsurprisingly) in what is now the western United States and northern Mexico, apparently fed on dinosaurs.

A reconstructed Deinosuchus hatcheri skeleton in the Natural History Museum of Utah.  [Image is in the Public Domain]

According to research published last week in The Journal of Vertebrate Paleontology -- which is why this whole horrifying topic comes up -- a combination of new fossil finds and re-analysis of old fossils, Deinosuchus was probably an ambush predator, like its much smaller modern Australian cousin.  It could, paleontologists believe, have taken down just about any of the dinosaurs alive at the time, up to the biggest ones.

"Deinosuchus was a giant that must have terrorized dinosaurs that came to the water's edge to drink," Adam Cossette, of the New York Institute of Technology College of Osteopathic Medicine at Arkansas State University.  "Until now, the complete animal was unknown.  These new specimens we've examined reveal a bizarre, monstrous predator with teeth the size of bananas."

During the time it was around -- the late Cretaceous Period, between 75 and 82 million years ago -- it lived in similar habitats to the Australian saltwater crocodile.  At that time, North America was split in two by a shallow sea that extended from the Arctic Ocean to what is now the Gulf of Mexico, and which covered most of what is now the Midwest and Southeast.  The Western Interior Seaway, as it was called, separated the small continent of Laramidia (now the Southwest, California, and the Pacific Northwest) from Appalachia (the mid-Atlantic, Northeast, and eastern Canada).  (If you're curious, the surreal, brightly-colored rock formations in what is now Bryce Canyon National Park, in Utah, were deposited at this time.  Hard to imagine that what is now high desert was once a shallow tropical sea, but it was.)

So Deinosuchus would have lived on both sides of that narrow sea, laying in wait for any prey to come along.  Also found in these same rocks are fossils of Pteranodon, the familiar crested pterodactyloid, along with hadrosaurs (duck-billed dinosaurs) and monstrous turtles like Archelon, which is estimated at five meters in length and weighing about two thousand kilograms.

Hard to picture that tableau as having occurred in what is now Kansas.

One of the weirder things about Deinosuchus is that it didn't make it to the Cretaceous Extinction.  It died out about 75 million years ago, missing getting fried by the Chicxulub Meteorite strike by a good nine million years.  What wiped it out is unknown, but there's a general pattern that if the environment changes, apex predators get hit the hardest -- they're usually slow-reproducing, and their survival depends on the entire biotic web being intact.  (Consider that most of the modern large mammalian predators are on the Endangered Species List.)

There comes a point where superlatives fail me, and I think I've hit it.  I'll leave the rest to your imagination.  Suffice it to say that while it was around, it was the unchallenged ruler of the Western Interior Seaway.  And honestly, cool as it undoubtedly was, I'm just as glad those aren't lurking around any more.  Australian saltwater crocodiles are terrifying enough.

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This week's Skeptophilia book recommendation of the week is by the brilliant Dutch animal behaviorist Frans de Waal, whose work with capuchin monkeys and chimps has elucidated not only their behavior, but the origins of a lot of our own.  (For a taste of his work, watch the brilliant TED talk he did called "Moral Behavior in Animals.")

In his book Mama's Last Hug: Animal Emotions and What They Tell Us About Ourselves, de Waal looks at this topic in more detail, telling riveting stories about the emotions animals experience, and showing that their inner world is more like ours than we usually realize.  Our feelings of love, hate, jealousy, empathy, disgust, fear, and joy are not unique to humans, but have their roots in our distant ancestry -- and are shared by many, if not most, mammalian species.

If you're interested in animal behavior, Mama's Last Hug is a must-read.  In it, you'll find out that non-human animals have a rich emotional life, and one that resembles our own to a startling degree.  In looking at other animals, we are holding up a mirror to ourselves.

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

Reptilian splits

One of my favorite lectures in my AP Biology class was about how there's no such thing as a reptile.

If you took your last biology class before about 1995, you probably learned about Class Reptilia, containing turtles, lizards, snakes, crocodiles, alligators, and a few other assorted groups.  The class was defined by having dry, scaly skin, internal fertilization, "amniote" eggs with shells, and hearts that had incomplete septa (the wall down the center that separates the oxygenated left side from the deoxygenated right side).

Well, the last one wasn't 100% true, and that should have been a clue to what was going on.  Crocodiles and alligators have four-chambered hearts, and are also partial endotherms -- they show some capacity for internally regulating their own body temperatures, just as birds and mammals do.

It was genetic testing that finally settled who was related to whom, and that was when a lot of us got a shock (not so much the evolutionary biologists, who kind of expected this was how it was gonna work out).  The word "reptile" has no real taxonomic significance, because it lumps together groups that really aren't very closely related, and excludes others that are closer.  Here's how this branch of Kingdom Animalia evolved:

As you can see from the diagram, the problem was birds.  Crocodiles are more closely related to birds than they are to lizards (despite superficial appearance); and if you throw dinosaurs into the mix, it becomes even clearer, because birds are dinosaurs.

Think about that the next time you feed the chickadees.

So if you throw all the reptiles together, by the rules of cladistic taxonomy, you'd have to include birds, and nobody much wanted to call birds reptiles.  So the entire Class Reptilia was broken up, now as three different classes: Lepidosauria (lizards, snakes, and the oddball tuatara of New Zealand), Testudines (turtles), and Crocodilia (obviously crocodiles et al.).  Birds have their own class (Aves).

But what this brings up is how such different-looking animals as turtles and snakes evolved from a common ancestor.  The differences between the different groups of reptiles is pretty dramatic.  The explanation has usually been that it was adaptive radiation, a phenomenon that deserves some explanation.

Adaptive radiation is when a group undergoes rapid diversification to fill many available niches.  The classic example is Darwin's finches, a group of birds on the Galapagos Islands, which descend from a common ancestral group that split up to occupy different niches because of bill size and strength (which determines what they can eat).  That's a pretty drastic oversimplification, but it captures the essence: many available niches, and a population with sufficient genetic diversity to split up and specialize into those niches.

Because of the "many available niches" part, adaptive radiation is most common under two scenarios: a population colonizing a previously-uninhabited territory (as with Darwin's finches), and remnant populations left after a major extinction.  This was what was thought to have powered the split-up of the reptiles -- the "Great Dying," the Permian-Triassic extinction of 252 million years ago that by some estimates wiped out 95% of life on Earth.

Nota bene: there is fairly good evidence that the trigger for the Permian-Triassic extinction was hypercapnia -- a sudden increase in atmospheric carbon dioxide.  This led to drastic warming of the atmosphere and ocean acidification.  The cause -- according to a paper that just came out two weeks ago in the journal Geology -- was massive burning of coal.  Sound familiar?  In this case the cause was natural; it's thought to have been triggered by massive volcanism.  But the end result was the same as what we're doing now by runaway use of fossil fuels.  I'd like to think this would be a cautionary note, but the world's leaders seem to specialize in ignoring science unless it can directly make them money and/or keep them in power, so I'm not holding my breath.

But back to the reptiles.  The study that triggered this post, which came out this week in Nature Communications, points out the flaw in the argument that the adaptive radiation of reptiles was due to the Permian-Triassic extinction.  According to recent analysis, the split up was already well underway before the extinction started.  And the extinction itself was sudden, at least in geological terms; from start to catastrophic finish, the whole event took about a hundred thousand years.  In geological strata, this length of time is a very, very narrow band.

Plus, the different groups of reptiles individually show drastically different rates of specialization. "Our findings suggest that the origin of the major reptile groups, both living and extinct, was marked by very fast rates of anatomical change, but that high rates of evolution do not necessarily align with taxonomic diversification," said study lead author Tiago Simões of Harvard University, in an interview in Phys.Org.  "Our results also show that the origin of snakes is characterized by the fastest rates of anatomical change in the history of reptile evolution -- but that this does not coincide with increases in taxonomic diversity [as predicted by adaptive radiations] or high rates of molecular evolution."

The end result of the study is that the cause of the adaptive radiation is unknown.  It probably was pushed along by the mass extinction -- the species that survived the hypercapnia and the resulting environmental devastation were set up to have a whole empty world to colonize.  But what was driving the split-up of the group prior to the extinction itself?

Unknown, but the current study shows that clearly the adaptive radiation had already started.

I love puzzles like this.  In science, there are almost always more questions than answers, and every answer brings up new questions.  But another feature of science is the conviction that there is an answer even if we don't currently know what it is.  And chances are, further study will elucidate what exactly was going on -- and what led to the fragmentation of a group that now, over 250 million years later, comprises some of the best-known and most familiar critters who have ever walked (or flown across) the Earth.

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This week's Skeptophilia book recommendation of the week is for anyone who likes quick, incisive takes on scientific topics: When Einstein Walked with Gödel: Excursions to the Edge of Thought by the talented science writer Jim Holt.

When Einstein Walked with Gödel is a series of essays that explores some of the deepest and most perplexing topics humanity has ever investigated -- the nature of time, the implications of relativity, string theory, and quantum mechanics, the perception of beauty in mathematics, and the ultimate fate of the universe.  Holt's lucid style brings these difficult ideas to the layperson without blunting their scientific rigor, and you'll come away with a perspective on the bizarre and mind-boggling farthest reaches of science.  Along the way you'll meet some of the key players in this ongoing effort -- the brilliant, eccentric, and fascinating scientists themselves.

It's a wonderful read, and anyone who is an aficionado of the sciences shouldn't miss it.

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

Changing the thermostat

Everyone knows that the human core body temperature is supposed to be around 98.6 F.  At least, that's what we all learned in seventh grade life science, right?

A more curious question is why 98.6 and not some other temperature.  Other mammals need different core body temperatures, but the range is remarkably narrow -- from elephants (97.7 F) to goats (103.4 F), only a 5.7 degree difference overall, and the vast majority of mammal species are in the vicinity of 98-100 F.

In my biology classes, I usually did nothing more than a hand-waving explanation that "our body temperatures are what they are because that's the temperature where our enzymatic and neurochemical reactions work at their optimal rate," but that's a facile analysis at best -- a bit like saying "bake the cake at 350 F because 350 F is the best temperature at which to bake cakes."  It might be true, but it doesn't tell you anything.

Last month we got a better explanation of what's going on than what I used to give (admittedly a low bar).  A paper in Molecular Cell with the daunting title, "A Conserved Kinase-Based Body-Temperature Sensor Globally Controls Alternative Splicing and Gene Expression," by a huge team led by Tom Haltenhof of Freie Universität Berlin's Department of Biochemistry, gives us a window into why we regulate body temperature -- and why things fall apart so quickly when the temperature isn't what it should be.

The team looked at the effects of temperature change not in mammals but in turtles and crocodiles -- which are themselves poikilothermic (known in common parlance as "cold-blooded") but have a temperature-switching mechanism for sex determination.  In crocodiles, incubation of the eggs at a warmer temperature results in males; in turtles, the pattern is the opposite.  (Some lizards have an even odder pattern, where intermediate temperatures result in males, and either low or high temperatures result in females.)

The question was how this was happening.  Something about the temperature must be changing the chemical signaling that guides embryonic development; but how?

Haltenhof's team found that there is a group of enzymes called CDC-like kinases that are extremely temperature-sensitive.  Kinases in general are a hugely important enzyme family that are responsible for phosphorylation, the main way energy is transferred in living organisms.  So if you affect the reaction rate of a kinase, it results in changes in the transfer of energy -- and can have enormous impacts on the organism.

And the CDC-like kinases, Haltenhof et al. found, were acting directly on the DNA, and changing the rate of gene expression.  In crocodiles and turtles, the type of gene expression affected had to do, unsurprisingly, with embryonic development of the reproductive systems.

So far, interesting only to geneticists and herpetologists (and, presumably, to the crocodiles and turtles themselves).  But where it caught my attention was when it was pointed out that the activity of CDC-like kinases is important not only in reptiles, but in humans -- and that overexpression of one of them, cyclin E, is connected with at least one form of cancer.

So this research seems to have implications not only for embryonic development in crocodiles and turtles, but in explaining why our own body temperatures are so tightly regulated.  The authors write: "[CDC-like kinase] activity is likely to also impact on gene expression in pathological conditions such as hypothermia, septic shock, and fever, or in the slightly warmer tumor microenvironment."  And since in general, the core body temperature drops as a person ages, it also made the authors speculate that this could be the key to at least some age-related malfunctions (and perhaps suggest a way to treat them).

[Image licensed under the Creative Commons 24ngagnon, Thermostat science photo, CC BY-SA 4.0]

This also brought to mind another perplexing bit of research that came out in January -- that the average human body temperature is dropping, on the order of 0.03 C per decade.  The standard "98.6 F" was established in 1851 by Carl Reinhold August Wunderlich, who determined this by taking the axillary (armpit) temperature of 25,000 people in Leipzig (and you thought your job was boring).  But a recent study with even more measurements found that currently, the average body temperature is almost a degree cooler than Wunderlich's value.

The speculation in that paper is that the drop in temperature is due to a decrease in the inflammation caused by exposure to infectious agents.  If the 25,000 Leipzig residents were a representative sample from the mid-19th century, 3% would have had an active tuberculosis infection, and that's just one disease.  So the lower average temperature today might have to do with our lower incidence of infections of various kinds.

But it makes me wonder what effect that's having on the CDC-like kinases from the first study.  Because during our evolutionary history, the 1850s condition of harboring infections was much more the norm than our current clean, germ-free-ness.  So while losing our collection of nasty bacteria might be overall a good thing, it might have caused a drop in temperature that could affect other reactions -- ones we're only beginning to understand.

That's yet to be established, of course.  But what it does highlight is how important the body's thermostat is.  Only a four-degree drop in core body temperature is a sufficient level of hypothermia to severely endanger a person's survival; likewise, a six-degree increase would be a life-threatening fever that (if survived) could result in brain damage.  We are only beginning to understand how our temperature is regulated, and why the effects of losing that regulation are so drastic.  But what this new research shows is that our body temperature might have far more ramifications for our health than we ever imagined -- and could be the key to understanding, and perhaps treating, diseases that have up till now defied medical science.

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This week's Skeptophilia book-of-the-week is brand new -- science journalist Lydia Denworth's brilliant and insightful book Friendship: The Evolution, Biology, and Extraordinary Power of Life's Fundamental Bond.

Denworth looks at the evolutionary basis of our ability to form bonds of friendship -- comparing our capacity to that of other social primates, such as a group of monkeys in a sanctuary in Puerto Rico and a tribe of baboons in Kenya.  Our need for social bonds other than those of mating and pair-bonding is deep in our brains and in our genes, and the evidence is compelling that the strongest correlate to depression is social isolation.

Friendship examines social bonding not only from the standpoint of observational psychology, but from the perspective of neuroscience.  We have neurochemical systems in place -- mediated predominantly by oxytocin, dopamine, and endorphin -- that are specifically devoted to strengthening those bonds.

Denworth's book is both scientifically fascinating and also reassuringly optimistic -- stressing to the reader that we're built to be cooperative.  Something that we could all do with a reminder of during these fractious times.

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