| 1 | The bear family tree of 2022 |
Before we delve into the mysterious world of long extinct bear species, you first need to understand the bear situation today. All surviving bear species are grouped into the wide family of Ursidae, which is itself divided into Ailuropodinae for giant pandas, Tremarctinae for the spectacled bear, and ursinae for all other bear species, the latter being collectively dubbed the “real bears”.
Within ursinae, there are six living species. Can you guess them all? Some are obvious, like the polar bear, brown bear and American black bear, but the remaining three are sloth bears, sun bears, and Asiatic black bears.
Despite the shaggy, blue-tinged coat of the Tibetan blue bear, or the lighter yellow coat of the Syrian brown bear, both are considered to be the same species as the marauding grizzlies of Yellowstone. “Brown bear” encompasses 20 subspecies around the world, including grizzlies, Kodiak bears, east Siberian brown bears, and recently extinct ones such as the Atlas bear and Californian grizzly.
Yet confusingly, the only two black bears to exist in the world, the American species and the Asiatic black bear, are distinct enough to be recognised as two separate species, rather than subspecies. Then there’s the polar bear, which keeps things simple for the layman with no subspecies whatsoever.
The official name of the overall brown bear species is ursus arctos. Within that we have such characters as ursus arctos horribilis (grizzly), ursus arctos middendorffi (kodiaks), and ursus arctos syrianus (Syrian brown bears).
| 2 | Ursus etruscus |
The fossils show that brown bears appeared in Eurasia sometime over the last 1 million years, so which bear was the immediate ancestor? It’s fair to say that a squirrel didn’t mutate into an 800 pound grizzly overnight. While nobody is completely certain, the main candidate is the Etruscan bear, or Ursus etruscus.
This bear species lived from 5.3 million years ago to just over 300,000, and its heartland was Europe, with no fossils ever discovered in America. This isn’t a mystery bear; there’s no debate over the Etruscan bear’s existence, as remains are abundant all over Italy, Spain, France, and even modern day Palestine.
Skeletal reconstructions show that ursus etruscus looked similar to the modern brown bear, but slightly smaller, as though one stage away from the finished article. A complete skull was unearthed in Val d’Arno in northern Italy, and the front incisors were just as brutally sharp as a modern bear’s. The jaw had an extra layer of premolar teeth, but according to microwear patterns, the Etruscan bear’s diet was probably just as meat-heavy as today.
According to fossils, ursus etruscus became larger over time, from the size of an Asiatic black bear 3MYA to only slightly below a brown bear 1MYA. The oldest known remains were found in Vassiloudi, Greece, at 5.3 to 1.8 million years old, while the most recent showed up in Asturias, Spain, dated to 1.8 million to 100,000 years ago. The exact dates for this bear ancestor are a bit of a blur.
| 3 | Ursus minimus |
Moving further back in time, we have ursus minimus, AKA the Auvergne bear. This is the widely theorised ancestor of the Etruscan bear, and it lived approximately 5.3 to 1.8 million years ago.
Once again, its fossils are almost entirely found in Europe, but being an extra rung down on the evolutionary ladder, ursus minimus looked closer to a modern day black bear than a brown bear. So similar, in fact, that some people believe that Asiatic black bears are a secret surviving population! The more accepted theory is that ursus minimus was the last common ancestor of black bears and brown bears, the point where the two species diverged for good. In fact, ursus minimus may be the ancestor of all modern bear species except for panda bears and spectacled bears.
Some believe that ursus minimus was slightly more carnivorous, but its molar teeth had all the flatness of modern bears, designed for chewing foliage like berries and roots. Ignoring weird offshoots like the plant-loving cave bear, it seems that the diet of the brown bear’s forefathers didn’t change much for millions of years. The main changes were size and appearance.
Like ursus etruscus, this ancient bear gradually became larger and larger, from the oldest known fossil in Stavropol’skaya, Russia (5.3-3.4mya), to the most recent in Sezene, France (3.4-1.8mya). One thing we’ll probably never know is the Auvergne bear’s (or Etruscan bear’s) fur colour – skeletons can only tell us so much.
| 4 | The ancient dawn bear |
We now leap back an entire 15 million years, to one of the commonest bear ancestors in the fossil records. Outside of obvious candidates like the woolly mammoth and giant sloth, this might be one of the coolest, most distinctive looking prehistoric mammals. Colloquially, it would be dubbed a wolf-bear-cat, because that’s exactly what it looks like.
In reality, it was (or is, there were no biologists then) called the dawn bear, or Ursavus elmensis. It lived around 20 million years ago and was the size of a fox, 45 to 85cm long when excluding the tail. Some biologists view it as the first “true bear”. This was still a tree-dwelling predator, but its carnassial, meat-shredding teeth were now smaller, and its molars had developed the flatter surfaces of modern bears used for grinding vegetation.
The dawn bear was part of the wider Ursavus family, which originated in Asia before spiralling into multiple diverse and wacky species. For example, ursavus elmensis spawned U. primaevus and U brevirhinus, before U.primaevus spawned U. ehrenbergi and U. depereti, bears which continually grew larger. Ursavus had dozens of members over the ages, but ultimately, they all went extinct.
At 20 million years old, the dawn bear was one of the earliest Ursavus species. In the end though, it’s the only one whose lineage is confirmed to survive, as the forefather of all surviving bear species.
| 5 | 5 to 20 million years ago |
So what happened in the millions of years between dawn bears and ursus minimus making its first appearance around 5MYA? Nobody is 100% sure, because the period is one of the murkiest in the whole timeline of bear evolution. Biologists barely understand the evolution of human beings from our savage (or maybe wise and thoughtful) ape ancestors, and past the mark of 5 million years, the story of bear evolution suddenly descends into a fog.
A common theory today is that the forefather of ursus minimus was a member of the protursus family, a long extinct bear genus, but compared to the Etruscan bear, archaeologists have unearthed almost no protursus fossils. Somehow, they identified protursus as an all-new bear family from a single tooth found near Barcelona in 1976, and declared it to be more primitive than ursus (the modern group), but more advanced than ursavus.
Protursus simpsoni is an oft-mentioned candidate for the brown bear’s evolutionary forefather, but that’s only because it’s the sole confirmed protursus species! Slowly, more fossils appeared, and p.simpsoni emerged as a proto bear the size of a small dog, with some classic bear characteristics starting to emerge: heavier limbs, square molar teeth, and a shorter tail.
| 6 | A long forgotten world of bears |
The fact is, however, that dozen of long extinct bear species lived during this murky period. 15 million years is a long time. Ursus minimus and ursus etruscus are more recent, and very well accepted, but protursus is on very shaky ground as a brown bear ancestor. The fossils of the real predecessor to ursus minimus might still be out there, buried in rock sediment in an obscure Mediterranean cave somewhere.
Another clue was a species called ursavus tedfordi, identified back in 2006 when a rare complete skull was unearthed in China. Dated back to 8MYA, it bore the closest resemblance to modern brown bears yet of an ursavus skull. At the same time, the skull had some peculiarities which modern brown bears lack.
The scientists concluded that it represented an offshoot, but from which species? This mysterious species might be the missing ancestor of ursus minimus and brown bears, rather than Protursus. Officially, the ursavus clan went extinct around 5MYA, so it fits the timeline well. Amazingly, the name has nothing to do with teddy bears: it was named after experienced bear researcher JH Tedford.
Tedfordi is also believed to be the ancestor of the Indarctos clan, the oldest of which is Indarctos arctoides (12.5 to 7.1mya). There’s also Indarctos atticus, which lived from 9.5 to 5.3 million years go, and had forelimbs strangely similar to the modern brown bear. Coincidence? As you can see, everything is still a big mess from 20-5 million years ago.
| 7 | The seal connection |
Before the dawn bear arrived 23 million years ago, we reach the earliest stages of bear evolution, unless you want to travel really far back to the era of dinosaurs and primitive mammals. Parictis was a genus of small, doglike bear animals, with 6 species inside the genus, all mostly found in North America. The fossils are mostly fragments, but the oldest ones date back 38 million years with the youngest dating back 33 million years (although these dates aren’t set in stone). These proto bears were tiny, with one skull measuring only 3 inches, but biologists have identified several similarities in shape to modern brown bears.
What about the age old question – are bears related to dogs? They are, but only distantly. They’re part of the wider order of carinova, but the bear family’s closest living relative, all 8 species of them, is the pinnipeds. The seals, the otters, and the blubbery, tusked walruses. If you stare hard enough, you can see some resemblance in the skulls of bears and seals today.
The fateful diverge took place approximately 50 million years ago, and the seals and cousins were preceded by the Amphicynodontinae family, which had a familiar long body, dwelt on land, but was slowly becoming semi-aquatic, like modern day otters.
In the 1990s, Amphicynodontinae was mistakenly grouped as a primitive bear species, showing just how tight the relationship is. As for dogs, the last common ancestor with bears lived around 60 million years ago.
| 8 | When did polar bears diverge |
As for polar bears, the popular theory is that they diverged once brown bears had already evolved, wandering too far north and becoming trapped by encroaching glaciers. They originally enjoyed a limitless buffet of seal, as similarly to Antarctica today, the seals had no terrestrial predators to worry about. But as the seals were forced to adapt, the bears were forced to evolve long snouts and white fur to make them more efficient predators. Polar bears were finally born.
For years, the spotlight was fixed on the ABC Islands of Alaska, which is a strange place for bear genetics, as the brown bears have a normal appearance and diet, yet an unusually close genetic profile to polar bears. Could polar bears have diverged in Alaska? It seemed logical, but then a theory emerged that the ABC Island bears were actually descendants of hybrids, caused by existing polar bears migrating south again and breeding with the locals.
The big stumbling block is that polar bears live on sea ice, and that their fossils tend to plummet into the ocean. Scratch that, they always fall into the ocean. The oldest polar bear fossils date back only 130,000 years, a jaw bone found in Prince Charles Forland in 2004. Some believe that rather than polar bears evolving from brown bears, the two were separate branches of a common ancestor, possibly ursus etruscus.
Polar bears are one evolutionary riddle which nobody is close to solving.
| 9 | The North America migration |
The oldest confirmed fossils of brown bears date back 500,000 years and were found in China, and its forefathers ursus minimus and etruscus were also Eurasian bears. So when did the American grizzly bears of Yellowstone Park or Canada enter the equation?
During the last glacial period, Alaska and Russia were connected by the land bridge of Beringia. Siberian bears crossed this bridge at least 100,000 years ago, the date when the earliest bear fossils in Alaska show up, but for years, the oldest confirmed fossils in Canada and the US were only 13,000 years old. The theory was that ancient bears were blocked by thick, impenetrable ice sheets, and stuck to the comparatively warmer coastline of Alaska instead.
Recently though, the timeline changed, as scientists discovered a 25,000 year old fossil in modern day Alberta, Canada. This created a mystery, because if the glaciers weren’t a problem, then why did brown bears wait another 12,000 years before invading the modern day United States and Mexico? One theory is the giant short-faced bear, which went extinct 15,000 years ago. It’s not proven, but this 2400 pound monster could have outcompeted the brown bear for territory.
It’s also theorised that brown bears crossed the Beringia bridge in 3 or 4 separate waves. One came from the Kamchatka brown bear of Siberia’s far east, and evolved into modern day Kodiak bears, while the others were East Siberian brown bears, who morphed into inland grizzlies. There’s many mysteries about bear evolution to unravel yet.
| 10 | The cave bear lineage |
Of the surviving bear species, panda bears were the first to break off, with the last common ancestor with brown bears living 20 million years ago. The American black bears which constantly steal your pizza probably evolved from ursus minimus, the black bear’s last common ancestor with brown bears.
It’s possible that ursus minimus crossed the Alaskan land bridge and then started evolving, or it may have commenced evolution before crossing. What’s confirmed is that a proto American black bear existed between the two called ursus abtrusus.
Then there’s cave bears, which appeared when a lineage broke off from Etruscan bears 1.8 million years ago and became ursus deningeri, the cave bear’s immediate ancestor. Also called Deninger’s bear, this is a recent yet barely known subspecies. It also lived in caves, died out around 100,000 years ago, and had a heavily plant-based diet compared to brown bears.
Several fossils were unearthed in the Cueva Mayor cave in Spain from 1990 to 1994, and its lower jaw and mandibular ramus had subtle differences in shape to a cave bear, including being smaller. Yet the longer, higher skull was already appearing, compared to the rounded skull of a modern brown bear. By 1 million years ago, the cave bear (ursus spalaeus) emerged as the finished article. U. spalaeus was the last of its lineage, dying out an estimated 24,000 years ago (75,000 years after U. deningeri), due to humans occupying its caves, and its more restricted plant-based diet.
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