Where did all the giant animals go?

So, the last post we looked at a few incredible giant animals we used to have - giant animals we call "megafauna".  I promised that in my next post we would look a bit more at the theories behind the mass extinction.  (On an unrelated noted, did you know there were like 5 mass extinctions before the origin of man (or at least from the fossil record of the origin of man?!).)  So, let's stop and think about it.

This isn't a new question; it's been posed by all types of persons ranging from virtually no education through topmost scholars.  Theories are as varied as the people asking, ranging from ostensibly far-fetched hypotheses to seemingly "commonsensical" ones.  Some of the proposed theories from scholars include:

• Hyperdisease impacting only certain species
• Comet impact
• Solar radiation
• Overkill
• Blitzkrieg (rapid overkill)
• Sitzkrieg (fire, habitat fragmentation, and introduction of invasive species and diseases)
• “Simple” climate and environmental change

Instead of reallly boring you with full studies on theories, how about I summarize various hypotheses and provide an opinion based on general plausibility from questions or challenges left unanswered by each author.  Trust me, you like this option better because it means I do the hard work and you get the snapshot!  Win-win, eh?!

Extraterrestrial Impact Event

The extraterrestrial impact event theorizes that the onset of the 1,000+ years of Younger Dryas cooling event coincided and the Pleistocene megafaunal extinctions (as well as extinctions of the Clovis people) because of an extraterrestrial (comet) impact (Firestone, 2009).  The author cites a carbon-rich black material (referred to as “black mat”) which can be found immediately covering Clovis kill sites.  Furthermore, the author states that no megafaunal fossil or Clovis artifacts are discovered above (stratified) the black mat.  The composition of the black mat appears to coincide with extraterrestrial components as well as carbon components which allude to a superheated shockwave and high temperature fires.  He points to the Carolina and Great Lakes “craters” as substantiation for impact areas.    You caught that, right?  The Great Lakes are craters.  That right there is going to cause me a lot of research sometime in the near future.

Anyhow, the back mat referenced by the author is seen in various articles and, as such, does seem to play some role in the overall extinction.  In regard to the proposed impact craters: the author argues proof of impact based on shallow "crater pools" in the 15 Carolina Bays as well as elliptical shallow lakes in Georgia, Virginia, Nebraska, Kansas, New Mexico and Texas; the inexplicable depth of the Great Lakes is why he states they were also formed due to some interstellar cause.  He provides ample imagery and ‘impact-related mineral data’ to explain the extraterrestrial-caused formation of the numerous shallow areas and Great Lakes.  In specific regard to the Great Lakes, he agrees that a large comet strike would have left craters but believes these craters were diminished in standard identifiable features.  He believes the comet struck the Laurentide Ice Sheet, which greatly absorbed some of the impact energy.  The impact caused the ice sheet to fail and, upon failure, provide a sudden release of both rushing water and ice ejecta.  Therefore, with circumstances being as they may, there would be no ‘tell tale’ crater but, instead, “a great scar in an otherwise featureless landscape.”  The author further links the formation of the Great Lakes to coincide with the formation of Charity Shoal, a 1km crater in Lake Ontario known to have formed near the time of the theorized Younger Dryas impact.   The author uses an image with an overlaid line to express that 3 of the 4 deepest areas of the Lakes are in a line similar to crater ‘chains’ previously observed on the Earth, moon, and Jupiter after the Shoemaker-Levy comet impact.   

While many of the data appear solid, my questions on this theory are many.  If the Pleistocene extinction - which included both highly adaptable people and animal species - was caused by an extraterrestrial impact, why were only select species eradicated?  Furthermore, the explanation may somehow work into the North American extinction event, but how does this tie into extinctions on other continents like Australia? Unfortunately for the author, other scholars also questioned the theory.  Firestone’s original journal entry apparently appeared in a National Academy of Science journal wherein his collection methods and theory garnered a rebuttal by Haynes, Jr. et al.   While the authors of the refutation do not negate the potential of an impact, the evidence was found to be lacking (and I'm pretty much in agreement).  The future article by Firestone in the Journal of Cosmology is, for all intents, the author’s second effort to provide substantiation for his impact-caused allegation for extinction.

The Super-Sized Solar Proton Event

The "super-sized solar proton event" is essentially a period of heavy, immense solar flare activity which caused enough radiation to impact large or unprotected species.  The author, LaViolette, provides proof through the Greenland ice records, carbon-14 and atmospheric carbon indicators in conjunction with 2 successive temperature maxima spaced by 1 solar cycle (one solar cycle is approximately 11 years so this event spans 22 years).  This raises his questions surrounding warming due to increased solar output which would substantially impact global climate.   It is evidence postulated by Firestone - that comet impact guy from the above study - that seemingly spurs LaViolette’s argument towards increased solar activity (as this active period would account for data reported by Firestone but also accounts for the lack of data to validate the impact theory). With LaViolette’s theory, only larger animals or unprotected (for example, humans as they were unaware of radiation concerns) would be impacted. 

LaViolette’s theory is relatively sound but, in and of itself and considering the span of time and the unequal disposition of the extinction but it still leaves a few questions.  Some are species specific... such as why wooly mammoth and not African elephants - was it just the external heating features?  Why the Smilodons (saber-toothed cats) and atrox (American lion) and not the African lion or many species of tigers or other large cats?  Simply put, it's likely this theory could not - even on the most forgiving judgement-lapsed day - be the sole cause of the Rancholabrean extinction. 

Blitzkrieg, Sitzkrieg, and Overkill

In the recent past a theory began to take ‘center stage’ surrounding the introduction of humans into previously unoccupied areas of the world as the primary cause for the Pleistocene extinctions (specifically the Rancholabrean extinction).  The basis of the theory surrounds an introduction of an exotic and invasive new, highly efficient predator (Clovis people, the original North American Homo sapien sapien) upsetting the balance for the large megafauna which exhibit slow maturation with protracted reproductive rates.   Proof for this theory is found at what is known as Clovis kills sites; areas where these people would clean meat and hides from kills.  Clovis kill sites often contain megafaunal remains such as mastodon and mammoth.  The efficiency of the Clovis people upset the balance as the mega-predators primarily fed upon the mega-herbivores.  The difference between “overkill” and “Blitzkrieg” is merely in the speed of the event. 

To coincide with this theory is the Sitzkrieg theory, which states that fires and exotic species (such as the Clovis people, for example) allowed for habitat fragmentation and introduction of diseases hereto unseen by the Rancholebrean megafauna.

Limited Scope and Tunnel Vision

But you know what? Regardless of how many articles I read, there seems to be evidence and granules of truth littered through each.  Trying to pinpoint the first ripple that started a chain of events in recent history is hard enough - but finding that first drip from 16 thousand years ago?!   C'mon, really? 

So, let's think for a moment.  There are things that are incontestable:

1. A large portion of Pleistocene epoch megafauna went extinct in, geologically speaking, a short amount of time.
2. Humans were present prior to the extinctions in other areas that still have megafauna.
3. There are mineral/cosmic remnants found in relation to the same general period of time.
4. There was a period of warming and massive reduction in glaciation.

When we simply look at the 4 points listed immediately above, therein may lay an answer.  Often we, as a society, look to find the root cause of an anomaly.  Yet if we take a snapshot of the past 100 years, it’s easy to see that one unnoticed event causes a trophic cascade (that's the drip/ripple effect I mentioned above) with people later attempting to decipher what happened first that caused the entire event.  It is very similar to the age-old riddle “what came first: the chicken or the egg?”.   In all likelihood, all of the rationale we know to be true contributed to the Rancholabrean and Pliestocene extinctions.  Solar activity leads to global temperature increases.  Those increases in temperature reduce glaciers and cause environmental change.  The introduction of new diseases and invasive species – especially highly efficient ones – impacts population rates.  Together, it seems highly logical to provide the insurmountable odds against survival for the largest mammals the world has seen.  So... sometimes we spend all our energy and effort looking for one reason when it was possibly the 'perfect storm' of climate change and species introduction.  Does it suck?  *&^% yes, it does.  I'd give my right hand to see some of the animals I blogged about before.

My love of my Smilodon knows no bounds - and I spend days on end dreaming of him. 

Ok. Enough of that.  if you're dying to see where I got my info, here's the wonderful world of science: 

Works Cited

Brook, Barry W. and David M. J. S. Bowman. (2002) Explaining the Pleistocene megafaunal extinctions: Models, chronologies, and assumptions. Proc National Academy of Science USA 99:14624-14627.
Campos, Paul F. et al (2010) Ancient DNA analyses exclude humans as the driving force behind late Pleistocene musk ox (Ovibos moschatus) population dynamics. Proc National Academy of Science USA 107:5675-5680.
Haynes, C. Vance Jr. et al. (2009) The Murray Springs Clovis site, Pleistocene extinction, and the question of extraterrestrial impact. Proc National Academy of Science USA 107:4010-4015
Firestone, Richard B. et al. (2007) Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling. Proc National Academy of Science USA 104:16016-16021
Firestone, Richard B. (2009) The Case for the Younger Dryas Extraterrestrial Impact Event: Mammoth, Megafauna, and Clovis Extinction, 12,900 years ago.  Journal of Cosmology 2:256-285.
LaViolette, Paul A. (2011) Evidence for a Solar Flare Cause of the Pleistocene Mass Extinction. Radiocarbon 53:303-323

Dreaming of Days Gone By

Pleistocene Epoch.  Rancho LaBrean Era... 

These are things that spur people to do the "70-degree head tilt" - i.e. ask a question like a canine - and

Yah... Usual Fodder so we know
who you're talking to.

wonder what you just said.  Not exactly normal words for conversation.  Unless you're a paleontologist... or me and a few of my buds?  I don't really understand how this brief period in the world's history can't absolutely astonish everyone.  The wonders of the world - far more comprehendable than the virtually alien world of the dinosaurs - were epic.  The big animals of that time - called megafauna - were seemingly created from dream-like visions of children.  

North American megafauna were nothing short of awe-inspiring.  People may see what we have now - the great grizzly, the popular polars, the  charismatic cougars - and think "those are pretty big".  Beyond our continental borders they see the elephants and the lions and the tigers and... well, surely those are seriously "mega" megafauna, right?  Hmmm... lets dream together, shall we?  Let me show you what we've lost through my eyes.

American Lions

American lions were the longest/tallest felids that have ever graced our planet.  Panthera Atrox.  Osteologic affinity to current lions and tigers... with heavy Eurasian cave lion resemblance.  We're talking about the biggest cat to roam the Americas.  Likely tawny and very similar to extant lions of today... only bigger!  We're talking seriously "mega".

Machairodontine Smilodon... 

...better known as saber-toothed felids or cats.  These were, quite simply, the most amazing cats that have ever graced our planet.  If we take a census of current (i.e. extant or still here) felids, a lot of people think that tawny-coated king of the jungle is the biggest.  Those people would actually be wrong.  The largest extant felid is the inappropriately named Siberian Tiger.  Dazzle your friends by calling this cat by their correct name: the Ussuri or Amur tiger.

I want you to picture the Amur in your mind.  We're talking about a splendidly-colored, 800-pound cat with the stealth and grace to vanish mere feet from your eyes in the forest.  Simply... vanish.  That's hard to comprehend that something so hulkingly large and vibrantly colored can simply vanish and only leave tracks.  Want an idea of how big? The average refrigerator is about the right size... granted it only weighs an average of of what... 250-350 lbs?  Here's a thought - here's a photo of Vladimir Putin with a female (smaller as they are dimorphic and the males grow larger).  The reason I need you to so accurately picture the size of this cat in your mind is to help you contrast the world's largest extant felid to the Smilodons of ages past.  This cat - even the small female here - could break bones with a swipe of a paw or, in the grasp of it's teeth, shake me like a doll and simply carry me off as a meal.

Putin with a 5-year old Amur female c/o Wonderful Russia

There were actually 3 species of Smilodon.  Smilodon gracilis, Smilodon fatalis, and Smilodon populator.  The gracilis was the smallest of the three, weighing in around 55-100 kg (or 120-220ish pounds).  This cat was tiny in that era, only the size of the current cougars, jaguars or leopards.  Then we have my "baby"... the Smilodon fatalis which is my most favorite felid in history.  The fatalis was the North American icon, really.  There's hundreds of relics left from this cat.  The fatalis weighed in between 160-280 kg (or 350-620 lbs). Now we're talking... this is a big kitty.  While some Amurs tip the scales at 800 pounds or more, the average Amur falls right in the size range of fatalis.  Maybe that correlation is why the Amur is my favorite extant species?  *shrugs*  Lastly, I need you to expand your mind and picture South America's populator - the last of our three saber-toothed felid species.  Populator was... epic.  Titanic.  Enormous. Gigantic.  How big, you ask?  Try up to 470kg (over 1,000 lbs).  The 'average version' of this cat tips the scales at what a rare Amur weighs; you know, the huge males that are flawless examples of Amur tigers.

Populator size - Deviant art - copyright attached

Moreover, you noticed (hopefully) that the Atrox was the longest while the Populator is the heaviest.  So... which is actually BIGGER?  Depends on if you look at size or mass. The differences?  These cats did differ from the leggy, fluid grace of the Atrox and extant cats we've mentioned.  While I'm sure Smilodons relied on stealth and ambush like today's felids, I want you to imagine a more compact, robust, stocky, muscular cat.  The difference I mention can be seen when you contrast a jaguar with a tiger.... the mass of the jaguar - the sheer ripple of muscle tightly packed under the skin, the slightly shorter legs, the size that belies the robust strength inherently possessed - is much like our Smilodon.  These cats were grapplers.  They would catch their massive prey and simply pull it down, overpowered by inconceivable strength. When grounded, the drastically large, curved, serrated sabers would then - with surgical precision - sever the tender flesh of the prey's neck and bring a hopefully quick and clean death.*  What a sight lingering throughout the ages.   

(*This is my interpretation of the hunting and killing methods of this cat; while there is scholarly debate, anyone saying these teeth were used to disembowel giant ungulates of the time really need to consider jaw structure and... if they need a visual... use a 'jawed staple-remover' to puncture a basketball.)

Finally, lets look at...

Arctotherium Angustidens and Arctodos Simus 

Angustidens and Simus are more commonly known as the short-faced bears (South and North American respectively) even though they aren't completely snub-nosed as the name would imply.  While ursids - bears - aren't my forte, there's no discussing the most mega without including these two.  Angustidens was the largest mammalian predator to walk our planet. Ever.  There's no adjectives that can really portray how amazingly huge these bears are.  Sometimes words simply fall short.  While there's debate on the hunting styles and dietary preference of these bears (omnivorous? carnivorous? active hunter or scavenger or cleptoparasitic?) they are still epic. Regardless, let's take a gander... I've nabbed some pics - mostly deviant art like the size comparison above, but one from NPS.gov.  Let's look: 

Simus

Angustidens

Grizzly, Polar, and Simus

Where did they go? 

So... now that we've had a moment to marvel at the greatest apex predators that vanished from our planet in our so-very-recent geologic past... why are they gone? I mean, it's not like all the megafauna went the way of the dodo.  Africa still has plenty.  So... why did Australia and the Americas fare so poorly?  Tons of theories.  Tons.  Some are so far fetched that I find myself rolling my eyes.  Others are plausible but, on the same token, likely not capable as stand-alone logic.  Maybe soon I'll have some more for you... we'll look at the theories together and postulate plausibility?  It'll be fun, really.  I mean, there's comet impacts and solar flares and some very "German-esque war machine sounding words" we can look at.  In the end, however, I think you'll agree with me that the likelihood of a single event causing anything isn't nearly as attractive a theory as a combination of events.

Enough of being indoors.... it's gorgeous outside... time to go out and PLAY!