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!