We'd like to thank Raycon wireless earphones
for supporting PBS. In 2013, a researcher working in the vast
collections of the National Museums of Kenya made a surprising discovery. Tucked away in a cabinet marked âhyenas,â
he noticed a large fossilized lower jawbone from some kind of carnivore. And it was big -- much bigger than the jawbone
of a lion, the largest carnivore in Africa today. Six years later, it was revealed to the public
as an enormous beast that was entirely new to science. It was named Simbakubwa kutokaafrika
And while its name literally means âbig lion from Africaâ in Swahili, this creature
was not a big cat. And even though it was found in a drawer labelled
âhyenasâ, it was not a hyena, either. It was a hyenodont, an extinct family of carnivorous
mammals that lived from the Paleocene to the Miocene Epoch, and inhabited Africa, Europe,
Asia, and North America. But Simbakubwa was not only unique because
of its large size. The fossil jawbone was excavated in the late
1970s at a site called Meswa Bridge in western Kenya that dates back about 26 million to
23 million years ago. It was from this jawbone that researchers
were able to estimate a range of potential body sizes for Simbakubwa, based on the size
of the molars and comparisons to living carnivores. And it looks like, at its smallest, Simbakubwa
was probably the size of a large lion, and at its largest, it couldâve been larger
than a polar bear. And it was a hypercarnivore - meaning: it
got more than 70% of its calories from meat! Based on its age and its monstrous size, Simbakubwa
is the oldest known giant member of its subfamily of hyaenodonts. These hyaenodonts gave the world some of its
largest terrestrial, carnivorous mammals ever known. And while these behemoths were the apex predators
of their time, theyâre not around anymore. It turns out that becoming the biggest, baddest
beast on the landscape can have serious consequences, when that landscape suddenly changes. Hyaenodonts are members of an extinct order
of carnivorous mammals called the creodonts. And even though they were super-carnivorous,
creodonts evolved independently from the order Carnivora, which includes all the modern felids
and canids we have today, among other critters. Creodonts are older and more primitive than
Carnivora, and they looked different, too. Their skulls were low with small braincases,
and their limbs were generally short and heavy. Early on in their evolutionary history, about
65 million years ago, the creodonts branched into two lineages, one of which was the hyenadonts. But the exact place they arose is still kind
of a mystery. Some experts think they originated in Africa;
others say Asia, and some suggest both, with a distinct group of hyaenodonts evolving on
each of the two continents. But the fossil and phylogenetic evidence we
have seems to suggest that they arose somewhere in Eurasia. And Simbakubwa was part of a subfamily of
hyaenodonts called the Hyainailourinae This particular group probably originated
in the region known as Afro-Arabia, which includes the whole Arabian Peninsula and northern
Africa, around 48 million years ago. From there, they spread into Europe, Asia,
and North America, where their large size and powerful bite ensured their position at
the top of the food chain. But by the middle Oligocene, roughly 30 million
years ago, it looks like they went extinct on the northern continents, maybe due to competition
from other groups of carnivores that evolved during that time. But in Afro-Arabia, they persisted, evolving
in isolation, separated from the newly-evolved carnivores in Eurasia by a seaway. And this isolation could have contributed
to the rise of giant hyaenodonts, like Simbakubwa. Because, it wasnât until the early Miocene,
around 23 million years ago, that evidence of the largest members of this group appeared,
approaching the size of a modern-day rhinoceros. What we know about Simbakubwa and its close
relatives comes from a very fragmentary fossil record, which is mostly made up of dental
remains and a few bones from the rest of the skeleton. This limited fossil record has made it hard
to figure out what their family tree -- or even they themselves! -- looked like. What we do know from their teeth is that these
hypercarnivores had to be able to process a lot of meat, which they did with specialized
teeth called carnassials. These are modified premolars and molars with
self-sharpening edges that pass by each other in a shearing motion - like a pair of scissors. Now, living carnivores usually have only one
set of these scissor-like teeth...but Simbakubwa and its relatives had three, turning their
jaws into meat-slicing machines. But making sense of the rest of their anatomy
is kind of hard. In order to sink those teeth into all that
meat, they had to catch it first. So researchers are really interested in figuring
out how these giant predators moved around. And the one clue we have about Simbakubwaâs
locomotion is pretty intriguing. Many modern carnivores are digitigrade walkers. This means that they walk up on their toes
with their heels in the air, making them faster than plantigrade walkers like us, who walk
with the soles of our feet flat on the ground. Digitigrade carnivores are more common in
open grassland environments, where that posture helps them save energy, and increases their
stealth, speed, and hunting success. And Simbakubwaâs well preserved heel bone
-- called the calcaneum -- was similar to that of one of its relatives, which has been
reconstructed as semidigitigrade - not all the way up on its toes, but not totally flat-footed,
either. Researchers also think that relative was
capable of making powerful leaps. So, based on similarities between the two
heel bones, itâs possible that Simbakubwa was also semi-digitigrade, making it a faster,
more agile hunter. All of these advantages -- a large body, three
sets of meat slicing teeth, and the ability to get around quickly -- probably led to the
success and survival of hyaenodonts through the Miocene Epoch. They likely hunted really large herbivores,
like the relatives of modern elephants and rhinos, occupying a niche that remains vacant
today. But, if they were such powerful beasts that
were so well-adapted to their ancient landscapes, then why arenât they still around? Well, the hyaenodonts met their demise by
the end of the Miocene, around 5 million years ago, thanks to an even more powerful forceâŚ
a rapidly changing environment. This period of change started back around
23 million years ago, as the Arabian Peninsula approached Eurasia, closing the seaway that
had kept Simbakubwa and its relatives separated from the carnivores of Eurasia. From then on, waves of animals were able to
migrate back and forth between the two regions. And among these migrants were hyaenodonts
from Afro-Arabia heading north, and carnivorans from Eurasia coming into Africa. This exchange of animal populations happened
at a time when Earth was undergoing major changes, like the formation of East Africa
Rift System, where two parts of the African tectonic plate started to move away from each
other. These changes led to dramatic transformations
in the Afro-Arabian landscape, with forests becoming drier and turning into more open
habitats. All of these changes spelled disaster for
the hyaenodonts, but researchers are still trying to figure out exactly how. There are two current hypotheses for the extinction
of Simbakubwaâs group: changing food webs, as environments changed and large herbivores
disappeared, or competition from modern Carnivorans. The first one suggests that when the
environment started to change, it was bad news for the large herbivores that hyaenodonts
relied on. Large herbivores tend to reproduce slowly,
which can lead to a rapid decline in numbers if ecosystems change too quickly, because
they canât adapt fast enough. Fewer large herbivores meant less food for
the large hyaenodonts, which werenât adapted to hunting smaller prey. This wouldâve made hyaenodonts more vulnerable
to extinction than the smaller carnivorans, which had a broader diet. The second hypothesis involves competition
from members of the order Carnivora as they moved from Eurasia into Afro-Arabia around
23 million years ago. Up to that point, hyaenodonts had been dominating
the predatory niches in Afro-Arabia. Fossil evidence suggests that the earliest
Afro-Arabian carnivorans were pretty small mesocarnivores, animals that get at least
half of their calories from meat and the rest from other things - think raccoons and coyotes. And theyâre usually less dramatically affected
by environmental changes than large hypercarnivores are. So, as new Carnivorans dispersed to Africa
from Eurasia, they became more diverse and started to compete with the hyaenodonts. Plus, Carnivorans with complex cooperative
behaviours, like living in packs, may have been able to steal prey from lone hyaenodonts. Between the changing environment, lack of
food, and the introduction of smart and sneaky competition, Simbakubwa and its relatives
might have simply met their match, after succeeding on three continents for at least 15 million
years. The evolution and extinction of these hypercarnivores
offers rare insights into a time that saw massive changes in the climate, oceans, tectonic
activity and the dynamics of many ecosystems. And as more fossils are found, we may be able
to recreate and better understand the African landscape in which they lived -- which is
also the landscape where our early ancestors evolved. Ultimately, the giant hyaenodonts of Africa
serve as a stark reminder that even the most powerful beasts are no match for a changing
world. Thanks to Raycon for supporting PBS Digital
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out is your thing. For more information go to buyraycon.com/eons. We hope you enjoyed this episode of Keeping
Up with the Carnassials. But I've always gotta give a shout out to this monthâs
Eontologists: Patrick Seifert, Jake Hart, Jon Davison Ng, and Steve! Go pledge your support at patreon.com/eons
and become an Eonite! And also thanks for joining me in the Konstantin
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at youtube.com/eons.
And PBS Eons messes up again....seriously this isn't the first time their videos showed questionable or even outright disproven hypotheses as fact.
- Simbakubwa was nowhere near as big as this video (or the study that described it) makes it out to be.I've explained this elsewhere.
- The hypotheses of carnivorans outcompeting hyaenodonts fails to explain why the two groups shared apex predator status in the Oligocene of North America and parts of Eurasia (and hyaenodonts managed to make it into the Miocene in the latter area). And pack hunting isn't really that common in Carnivora, so most carnivorans don't (and probably didn't) have that as a competitive advantage, either.