Monthly Archives: January 2014

Marine Megafauna on Coursera

I just signed up for Marine Megafauna: An Introduction to Marine Science and Conservation, and maybe you’d like to sign up too.  Marine Megafauna is a mooc (massive open online course) available to everyone, for free, via coursera.org.  The course website promises that by reading papers published in the open-access scientific journal PLOS ONE, you’ll “explore how marine animals have adapted to the challenges of a cold, dark and deep ocean” and learn, among other things, “how penguins keep warm, how blue whales eat and how everything in the ocean – from the biggest creature to the smallest – is connected.”  Sounds good to me.

Marine Megafauna starts on February 3.  Check it out.

(Or if you prefer your megafauna extinct, there’s an available session of Dino 101: Dinosaur Paleobiology, a course I’ve taken, enjoyed, and mentioned here before.  The current session started on January 6, but fear not! — the entire course is open for you to take at your own pace.)

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How Polar Bear Fur Works

Polar bears are tremendously impressive — the very definition of charismatic megafauna.  They’re cute and fluffy but also huge and powerful.

Polar bears in Alaska, courtesy of Alan D. Wilson via wikimedia commons.

Of those four factors, though, it’s not cuteness, size, or strength that impresses most: it’s fluffiness.  Fluffy fur is what lets polar bears survive the frigid temperatures of the Arctic.

Just how does fur work to keep polar bears a balmy 37 degrees Celsius in -40 degree weather?  A new paper by physicist Priscilla Simonis and colleagues illuminates the insulating power of polar bear fur.

As a general rule, insulation limits heat transfer.  Perfect insulation for a polar bear, therefore, would mean that heat transfer between warm polar bear skin and the cold Arctic air is zero.  The polar bear stays 37 degrees without cooling down, and the air remains -40 degrees without warming up.

Often it is presumed that fur works as an insulator primarily by trapping pockets of warm air with very low heat conductivity.  (Until now, some version of this explanation is probably what I would have told my not-quite-three year old had she thought to ask how fur keeps animals warm.)  But Dr. Simonis recognized that this model was too simplistic — the low heat conductivity of air couldn’t fully account for keeping polar bears with 5-inch-long fur a full 77 degrees Celsius higher than the -40 degree background temperatures of the arctic.

Conduction is only one of three methods of heat transfer.  The other two are convection and radiation.  With polar bears, there’s probably not much heat transfer occurring via convection.  This is because convection requires air movement and the air beneath a layer of polar bear fur is generally pretty still.  (This is another insulating benefit of fur.)  That leaves radiation.

Dr. Simonis figured out that, in a universe stripped of several possible confounding variables, polar bears would likely suffer about ten times as much heat loss from radiation as they would from conduction.  So for polar bears to survive in the Arctic, their fur must be countering that radiative effect in some very significant way.

Gradually extrapolating from simple to more complicated mathematical models, Dr. Simonis showed that two elements are necessary to create this type of significant insulating effect against heat loss by radiation:  First, she noted that there is a “rapid decrease in heat transfer rate with [an] increasing number of intermediate absorbers.”  In other words, to achieve insulation against radiated heat, there should be lots of objects — individual strands of fur, say — between polar bear skin and the cold, cold air.  Second, for each of these intermediate objects there should be “small absorption with high reflectances.”  What does this mean?  Well, radiative heat loss occurs via infrared radiation (this is the principle that allows for thermal imaging).  And white surfaces reflect all colors of light, including infrared.  Therefore, to best reflect infrared radiation and insulate a polar bear, its fur should be white.

(It helps that polar bear skin is black and quite able to reabsorb infrared radiation reflected by the white fur.)

The takeaway: polar bears’ white fur serves a dual purpose — it camouflages them in the snow, as you already knew, and it traps their radiated body heat.  Or, to use Dr. Simonis’s words, “The structure of polar bear or snow fox fur is actually multifunctional, providing both visual camouflage and good thermal insulation.”  Impressive.

(So impressive, in fact, that Dr. Simonis proposes using what I’ll call the “polar-bear-fur principle” for improving insulation in such high-tech applications as thermal shields for satellites.)

Reference:

P. Simonis, M. Rattal, E. M. Oualim, A. Mouhse, and J. Vigneron (2014) Radiative contribution to the thermal conductance in animal furs and other wooly insulators. Optics Express, Vol. 22, Issue 2, pp. 1940-1951.  doi: http://dx.doi.org/10.1364/OE.22.001940

New Quetzalcoatlus and Therizinosaurus Figures in 2014

I’ve previously written about some bizarre late Cretaceous creatures.  There are azhdarchid pterosaurs like Quetzalcoatlus — huge beasts with wingspans up to 35 feet that could stand up to 20 feet tall when prowling prehistoric prairies on foot and snacking on sauropod hatchlings.  And there are therizinosaurid dinosaurs like Therizinosaurus — long-necked, small-headed, beak-faced, feathered plodders with truly gigantic claws.

These are some of my favorite ancient oddities.  So today I got to revel in my nerdiness when I learned, courtesy of the Dinosaur Toy Blog, that model-maker CollectA will be introducing new figures of Quetzalcoatlus (complete with baby sauropod snack) and Therizinosaurus this year.  On the off chance that this excites you as much as it does me, I include pictures below for your enjoyment:

CollectA 2014 Quetzalcoatlus, courtesy of Dinosaur Toy Blog.

CollectA 2014 Therizinosaurus, courtesy of Dinosaur Toy Blog.

There are other Quetzalcoatlus and Therizinosaurus figures out there, but none (that I’ve seen) captures the research as well as these new ones do.  Sadly, neither figure appears to be available yet in the United States.  However, I believe Quetzalcoatlus is due out imminently and Therizinosaurus should be out by midyear.

A Beast With Two Names

Back on January 11, I read this on twitter:

Ross Barnett @DeepFriedDNA: It seems that when I wasn’t looking, P atrox has been renamed Naegele’s giant jaguar, thanks to a generous $ donation

Hm?  What was that about?

Panthera atrox was a big cat in the fullest sense of those words.  Significantly larger than the modern lion, it roamed what is now the United States until a global deep freeze killed it off around 11,000 years ago.

For various reasons, P. atrox was classified from the outset as part of the lion family.  But for decades, some scientists pushed back against this leonine designation.  They argued that the beast shared too many jaguar affinities to be classified as any other kind of big cat.  In 2009, a paper by Per Christiansen and John Harris claimed to settle the debate.  Comparatively analyzing the skull morphologies of different species (apparently more or less the same way Christiansen studied clouded leopards), the authors boldly stated that “Panthera atrox was no lion.”  Instead, they proposed, “A possible scenario for evolution of P. atrox is that it formed part of a pantherine lineage that … gave rise to the extant jaguar.”  As P. atrox, in these authors’ estimation, was no longer a lion, but rather something jaguar-ish, it was due a new name.  To honor an ancient-mammal enthusiast and donor to the Natural History Museum of L.A. County, P. atrox was christened “Naegele’s giant jaguar” [pdf].

Because P. atrox was originally classified as a lion, however, it is more likely that you know it as the “American lion.”  And over the decades, this leonine designation has largely resisted any jaguar-ish pushback.  In 2009, a paper by Ross Barnett and colleagues claimed to settle the debate [pdf].  Comparatively analyzing the DNA of different extant and extinct big-cat species, the authors dispassionately stated that “all late Pleistocene lion samples produced sequences that grouped strongly with modern lion data, rejecting any postulated link between atrox and jaguar.”  Indeed, they said, P. atrox was a lion — or at least something lion-ish.  If we accept this classification, then P. atrox may keep and proudly bear the “American lion” moniker.

In my world, DNA analysis trumps skull morphology.  “American lion” wins.

But I’m not the final arbiter of such things.  As long as there’s a dispute, poor P. atrox must suffer from an identity crisis.  For now, it’s still a beast with two names.

Note:  For those interested in more detail on the dueling 2009 P. atrox studies and the quite divergent implications of the two different proposed classifications, the estimable Brian Switek has a much longer read on the topic.