I’d like to start by extending my personal thanks to a certain wolf that lived in North
America, back in the Pleistocene Epoch.
He was an average-sized adult male, probably around 65 kilograms, and … he’d done a
lot of living in his time.
He was stalking around what’s now Southern California when he, and his pack, heard a
noise -- the sound of an animal in distress.
Maybe a bison, or a camel, or a ground sloth.
So the wolf and his pack went toward the sound.
Because, when you’re a wolf, the sound of prey in distress might as well be a dinner
bell.
He found the animal stuck in a pit of thick, black, smelly goo, trapped.
So he moved in for the kill.
Until, he found himself trapped.
I don’t know the name of this particular doggo.
But I do know that he existed.
Scientists refer to one of his bones as LACMHC 8291.
This wolf was only one of thousands of his species to die in this same spot in southern
California, over the course of thousands of years.
And I want to thank him, because the way in which he and his compatriots died that day,
has allowed us to learn an incredible amount about their species.
Their remains have taught us volumes about how they lived.
How they hunted.
How they died.
And way more about any individual animal’s sex life than you’d ever want to know.
The specimen known today as LACMHC 8291 belonged to the greatest species of wolf that ever lived
The dire wolf.
Ok now no, this is not a Game of Thrones fan fiction episode.
Dire wolves were real!
They were among the most impressive members of the family Canidae, which has its roots
in North America.
Today canids include wolves, foxes, coyotes and dogs, all over the world.
And the biggest canids that ever lived were the borophagines, also known as the bone-crushing
dogs, which I’ve talked about before.
But around 30 million years ago, a new subfamily of canids appeared: Caninae, or canines, the
true dogs.
And at first, canines were pretty small, around the size of a fox.
Which was fine, because the bone-crushing dogs and cat-like nimravids already occupied
the role of large predator, so being small let canines take advantage of smaller prey
with less competition.
It took 23 million years before the ancestors of the dire wolves developed bigger
body sizes that could take on bigger prey, with canines the size of coyotes showing up
around 12 million years ago.
But it wasn’t until about 3 million years ago, when the borophagines were declining,
that canines started to become wolf-sized.
And the most massive of these was Canis dirus, the dire wolf.
It lived in North America from about 840,000 to 11,000 years ago.
And it’s also found in the fossil record of South America, from about 27,000 to 11,000
years ago.
So for nearly a million years, Dire wolves were widespread and abundant throughout the
Americas, found in grasslands and forests, and at elevations as high as 2200 meters.
And because they were so common, we have lots of fossils of them, which has given us an
especially vivid understanding of their biology, ecology, and behavior.
But no place in the world has shown us the life and death of dire wolves in as lucid
detail as the La Brea tar pits, where literally thousands of their remains have been unearthed.
This includes mah boi, the owner of the bone labelled LACMHC 8291.
Today, these tar pits are smack in the middle of downtown Los Angeles, and it’s a fascinating
place.
It’s full of these pools of what’s commonly called tar, but is actually naturally occurring
asphalt -- basically a sticky, viscous version of petroleum.
And back in the Pleistocene, these asphalt pits were a textbook example of a predator
trap.
The pits simply trapped any animals that made the mistake of wading into them.
And once trapped, those animals’ distress calls would draw predators to the scene.
But then, the predators would get stuck too – just like that wolf I told you about -- and
then their calls would in turn summon even more predators.
As a result of this grim dynamic, dire wolves are the most common fossil found at La Brea,
bar none, with more than 4,000 individuals found so far.
That’s more than mammoths or saber tooths or even today’s ubiquitous coyotes.
And with so many fossils at their disposal, paleontologists have been able to find outan
awful lot about Dire wolves.
For one thing, we know a lot about their true size.
The average dire wolf was about 60 to 68 kg, which is 20 kg heavier than the average of
their close cousin, the Gray Wolf.
And it’s about 45 kg heavier than the average Coyote.
But even though Gray wolves and Dire Wolves were very different in their average weight,
they were probably quite similar in height and length.
Dire wolves were just stockier, with stronger bites and broader faces – a bruiser of a
wolf.
It’s likely that packs of dire wolves hunted bison, camels, horses, and other large Pleistocene
animals – though probably not adult mammoths.
I mean, Dire wolves were big, but not that big.
But the bones at La Brea can even tell us how dire wolves hunted.
And how hard it was on their bodies.
Bone injuries in fossils tend to look like areas of strange texture – bumpy and overgrown,
or with pitted surfaces where bone is normally smooth.
Some bone injuries leave marks that are so distinct that scientists can even diagnose
specific diseases – like tuberculosis in mammoths, or infections caused by a blow from
a Stegosaurus’ tail.
Which actually has happened.
And many of the dire wolf bones at La Brea turn out to be pathological, meaning they
show signs of things like infections, disease, or some sort of developmental deformity.
And among those pathological bones, 2% are the result of trauma, like fractures.
And one of them is that bone I told you about: LACMHC 8291.
Signs of trauma in dire wolves tend to be in the ankle, the wrist, or the neck.
Which are typical of pursuit predators.
So this suggests that the wolves were getting hurt while chasing down and subduing their
prey.
And dire wolves in La Brea also have a lot of broken teeth.
This probably came from eating the bones of their prey.
The bones of big herbivores contain a lot of fat, juicy marrow.
And while dire wolves didn’t have the jaw strength of their cousins, the borophagines,
they could still crack open bones.
That marrow was just worth the risk of breaking some teeth.
And even the unusual number of dire wolves at La Brea tells us a lot about their behavior.
About a third of all the specimens at La Brea are Canis dirus.
So either they were just incredibly common, or, more likely, they were the sort of animal
that hunts down animals in distress: pack hunters.
I mean, it’s not every predator that hears an animal in distress and decides to check
it out.
In Africa today, about 85% of the predators that respond to playback tapes of animals
in distress are social predators, predators that hunt in packs.
And hunters tend to respond to these sounds in groups, because they might need backup
to fight off other hungry predators that were drawn to the same sound.
Which is pretty clever.
At La Brea, this behavior is reflected by the fact that about a third of the dire wolves
found in the pits were juveniles -- puppies, following their pack to learn how to hunt.
..I can't believe you're making me talk about dead puppies
But maybe one of the most interesting insights into the behavior of dire wolves from La Brea
is an abundance of a small, rarely fossilized bone called a baculum.
A baculum is, quite simply, a penis bone.
Not all animals have them, as you’ve probably surmised, but carnivores, rodents, and many
primates do.
And about 400 bacula of Dire wolves have been preserved at La Brea – which has allowed
us to study their size and shape for clues into their mating behavior.
A dire wolf baculum is about 15 cm long, and 1.5 to 2 cm thick.
That’s 2 and a half times as thick as the baculum of a gray wolf, and it's 1.5 times as long.
Or, if you prefer, it's 5 times as large by volume!
So, why was this unusually large piece of equipment necessary?
Well, it probably had to do with pack structure.
Among Dire wolves, males and females were about the same size, just like we see in most modern
canine species.
And they were probably forming packs with equal numbers of males and females, again, like
modern wolves do today.
So, males had to compete with other males a lot for access to breeding females.
But we know from their sheer numbers that dire wolf packs were probably larger than
those of modern wolves.
And we also know that larger packs mean more competition for mates.
And: modern animals that experience more male-to-male competition typically have larger bacula.
For example, the largest of these bones by far belong to walruses, which live in groups
of up to 20,000 during mating season.
And their bacula can be 45 to 60 cm long.
Wait
Why'd the music stop?
I'm not making a joke.
You think I'm going to say something?
I have nothing to add. Let's just carry on, shall we?
Longer bacula can help a male compete, because they’re associated with what’s called
prolonged intromission, or longer periods of copulation.
This helps keep other males from having access to the female.
But having a wider baculum is thought to offer a different advantage.
And that is, fights between males can break out during the act of mating– and fighting
while copulating can cause your baculum to … snap.
Having a thicker baculum means you’re less likely to get injured during mating, so you
can mate successfully and pass on your genes.
And, sure enough, of the 400-some bacula found at La Brea, only 8 show signs of injury and
rehealing.
And one of them … was that same specimen that belonged to the hero in this story, LACMHC
8291.
This bone is a baculum, and it not only fractured, it was broken in half.
And then, the fractured segment of bone got turned around, and re-fused at an angle.
So yeah.
That’s why I said that particular male wolf had done a lot of living.
He’d … seen some stuff.
But the point is, overall, Canis dirus had far fewer broken bacula than you’d expect
-- evidence that these wolves were well-adapted to a lifestyle where sexual competition was
fierce.
As we’ve mentioned before, proving any sort of group behavior in the fossil record is
really hard.
But we’re able to do exactly that for the biggest wolves that ever lived, because of
the massive sample size at La Brea and other places.
Thanks to those sticky pits of asphalt, we know that dire wolves were truly big, really
mean to each other during mating, could crack open bison bones, and, by all accounts, were
very successful during the Pleistocene.
Yet despite that, they went extinct at the same time as most of the Pleistocene megafauna
– around 10 to 11 thousand years ago.
The reason for that extinction, as you know, is hotly debated.
Was it caused by a fast-warming climate?
Or the appearance of human hunters?
Or both?
No matter the cause, during that time, many of the biggest herbivores went extinct, leaving
the dire wolves with less food.
Without large prey, and without being able to adapt to smaller prey, to compete with
smaller canines like coyotes and gray wolves, the dire wolves disappeared.
That’s why today, they’re only found in museums, like the one in Los Angeles where
LACMHC 8291 is still housed.
It remains today as a reminder of that narrow window of often-dire times, when the dire
wolves lived and thrived.
Thanks for joining me again today!
And extra-big thanks to our four eontologists, David Reed Rasmussen, Jon Ivy, Eric Lawrence,
and Steve.
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