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Saturday, 25 November 2017

Miocene (Pt 4): Bear-Dogs and Dog-Bears

Amphicyon
Many of the animals we would see in Early Miocene Europe, were we able to visit, would be of broadly recognisable types: deer, pigs, antelopes, rhinos, and elephant-like mastodons. True, many of these are nor animals we would expect to find in Europe today, and the individual species were, of course, different from the modern sort, and in some cases quite dramatically so. But they at least have identifiable relatives today.

But all of the animals I've just mentioned are herbivores. Yet, when it comes to the larger predators of the day, we instead find that most of them were rather different, lacking close modern relatives. While more recognisable carnivores did, in fact, turn up as the Miocene progressed, at least in the beginning, the majority were survivors from an even earlier time, before many modern kinds of animal had arisen.

There are a couple of caveats to this, however. Firstly, we should note that there were some herbivores in the same situation, notably the chalicotheres, even if, proportionately speaking, there weren't quite so many. More significantly, at least by the end of the Early Miocene, this was really only true of the big carnivores, not the small ones.

I'm not referring to insectivores here, although, yes, we did have things like hedgehogs and moles around  - the latter, for instance, had been subterranean for millions of years before the dawn of the Miocene. For that matter, we do know of quite a few fossil bats from the time, some of which were almost identical to modern forms. But, no, I'm referring to actual carnivorans, likely preying on things like rodents.

At the very dawn of the Miocene, the only mustelids in Europe were primitive holdovers from the preceding epoch, such as Plesicits, but over the next few million years they began to diversify, producing the first members of more recognisable groups, such as martens, otters, and wolverine-like animals. There were also some small carnivores in Early Miocene Europe that are no longer found outside of the Americas, including such things as early skunks and members of the raccoon family. At around the same time, early immigrants from Africa included some of the first mongooses and viverrids.

But, when it comes to the larger carnivores, things were, indeed, rather different.

In fact, there were two dominant groups of large carnivore in Europe at the dawn of the Miocene, and neither of them survive today. Of these, perhaps the more significant in the longer term were the amphicyonids, or "bear-dogs". These were neither bears nor dogs, but an entirely separate family of carnivore, albeit one that was probably closer to the dogs than to anything else.

Indeed, the early forms looked quite dog-like. One of the most common in Europe at the dawn of the Miocene was Cynelos, a survivor from the preceding epoch, which also had species living as far apart as Uganda, Pakistan, and Delaware. It was small by the standards of later bear-dogs, with the smallest species estimated as weighing just 23 kg (50 lbs), about the same as a springer spaniel or border collie. Larger species did exist, with one thought to weigh about 85 kg (190 lbs), putting it near the upper range of modern mastiffs. In general though, the shape of their limbs suggests that these early bear-dogs were fast runners, chasing down their prey as dogs do, although (also like dogs) they probably weren't absolutely pure carnivores.

While it survived longer elsewhere, Cynelos did not remain in Europe for long, where it was instead replaced by a number of other, more specialised, bear-dogs. Some became even smaller, reaching a peak with Pseudarctos of Slovakia, which had relatively large molar teeth, suggesting an omnivorous diet that might have had it competing with the local raccoons. Weighing just 9 kg (20 lbs), it was about the size of a bichon frise or dachsund, but, unlike either of those animals, had limbs that suggest it could climb trees.

Most of the bear-dogs, however, became larger. Pseudocyon retained the long limbs of its ancestors, and would have looked quite a like a dog - aside from the fact that, at around 125 kg (275 lbs), it would have been the size of a black bear. It also had slicing teeth that suggest that it was rather more adapted to pure meat-eating than Cynelos, and it, too, was presumably a pursuit predator.

It wasn't alone in developing a more exclusive taste for meat. The early form Ysengrinia, known from Spain to Japan, was already somewhat evolved along that path, but the best example from this time would probably be Agnotherium from Middle Miocene France. This was notably larger than a black bear, with similarly heavy limbs, but a more elongated, dog-like head. This had sharp flesh-slicing teeth that would probably have made it more dangerous than an equivalently sized, but omnivorous, bear.

But this was by no means the largest of the Miocene bear-dogs in Europe. That honour probably goes to Amphicyon, from which the group as a whole takes its scientific name. This was about the size of a full-grown grizzly bear, and had a similar build and limb proportions. However, the head was narrower and more dog-like, and the animal had a long tail and cat-like hips. The shape of its teeth and the presence of attachments for massive jaw muscles suggest an animal that may have been as much a scavenger as an active predator, since they seem well suited to crushing bone. However, it must have hunted live prey too. Indeed, the body shape suggests that it struck from ambush, like lions do, although it may perhaps have been more prepared to chase something that escaped the initial pounce.

Not long after the dawn of the Miocene 23 million years ago, the bear-dogs in Europe were faced with the appearance of an entirely new kind of competitor: actual bears. While they spread quite rapidly across Asia, and even into North America, our current best guess is that bears first evolved in Europe, with the oldest definitively dated fossil bear, Ursavus elmensis, dating from Early Miocene Germany. (Claims of older species seem to be disputed, and are based on fragmentary samples).

Ursavus - other species soon followed the initial one - was small by modern standards. With an estimated weight of about 80 kg (175 lbs), it would have been about the size of the smallest species of bear alive today, the sun bear of southeast Asia. However, despite its primitive position on the family tree, it was already more or less bear-shaped, and had teeth suited to an omnivorous diet little different to that which bears consume today. Opinions differ as to how close to the actual ancestor of all bears it might be; it's almost certainly the ancestor of most typical bears, but, while the first panda that we know of didn't appear until much later, it's unclear as to whether Ursavus is also their ancestor too, or whether some undiscovered proto-panda was already in existence by its time.

Appearing somewhat later, and distinctly less bear-shaped was Hemicyon, the best known member of a group of animals called the dog-bears. Initially thought to be rather dog-like (hence the scientific name, which translates as "half-dog"), some authors consider dog-bears to be, like bear-dogs, an entirely separate family of carnivore. Most, however, consider that, while bear-dogs are neither dogs nor bears, dog-bears are, in fact, bears (and not dogs). I hope this is all making sense...

(Of course, it doesn't help that there is a third group of animals, the arctocyonids, whose scientific name translates as "bear-dogs". These were something else entirely, and were, perhaps fortunately, long extinct by the time under discussion).

Although it had a number of bear-like features in its skeleton, betraying its ancestry, Hemicyon really didn't look much like our modern image of the animals. They had a slender body, about 1.5 metres (5 feet) long, with a short bear-like tail, but long wolf-like legs and teeth suited more to meat-eating than to omnivory. Like wolves, and unlike living bears, they walked on the tips of their toes, something typically seen as an adaptation for speed. So, a predator that's faster than your average bear, then...

There were, at least in Europe, no dogs to live alongside these various animals, because dogs had yet to leave their original home in North America. But, even before the first true bears appeared, bear-dogs were not without competitors as large predatory carnivores, and next time, we will see what was going on amongst the more cat-like animals of the day...

[Photo by Scott Nichols, from Wikimedia Commons.]

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