Sunday 8 July 2018

Miocene (Pt 8): Giant Honey Badgers and European Pandas

A great many predators lived in Europe in the glorious warmth of the Mid Miocene, when the continent was lush with subtropical vegetation and the herbivores that fed on it. As the climate began to turn, and the forests gave way to more open terrain, both the herbivores and the animals that preyed on them underwent a number of changes, with the latter in particular suffering some loss of diversity. (At least, so far as we can tell from the incomplete fossil record).

This affected the full gamut of mammalian carnivores, including many of the smaller, less obvious, ones. The boundary between the Middle and Late Miocene is an arbitrary one that isn't really marked by anything much in Europe, so that, to begin with, these were as numerous as ever. There were badgers, such as Sabadellictis, and even skunks, which today are not found outside the Americas.

Among creatures that we'd expect to be small today, but were sometimes less so back in the Miocene, the over-sized otter Sivaonyx seems to have originated somewhere around Thailand, but reached Turkey and Germany around this time, and Africa not much later. There was also the giant honey badger Eomellivora fricki, sometimes placed in its own genus, Hadrictis, to distinguish it from earlier, smaller relatives. Known from Late Miocene Austria, this is estimated to have weighed something like 50 kg (110 lbs), putting it in the range of some of the largest dog breeds alive today.

But this diversity was not to last, and, when the real climactic changes began, there seems to have been a die-back across the board. While the weasel-like animals were among those affected, perhaps the greatest long-term damage was suffered by the bear-dogs. These were neither bears nor dogs, although they shared features with both, and were, indeed, related. During the Middle Miocene, there had been a number of species of this animals in Europe, with fair range of sizes and lifestyles. When the climate cooled, they almost all died out.

The last known to have survived in the west of the continent was Magericyon, a moderately sized species from Spain. While noticeably smaller than any living bear, its teeth suggest that it had a more heavily meat-based diet than its ancestors, while the apparent size and presumed strength of its neck muscles suggest that it could have rapidly torn a carcass apart, perhaps to finish its meal before something larger turned up to steal it. Furthermore, it avoided competition with such things as sabretooths by moving out of the dense forests to more open woodland habitat, where it may have preyed on animals such as musk deer.

Once it had gone, however, the only genus that remained in Europe lived further north and east; Amphicyon, a much larger form that would have particularly resembled a dog-headed bear. Even here, the earlier species were replaced by newer ones that appear to have been less numerous, and that are known from relatively small numbers of fossils from Germany, Austria, and Hungary. Larger than their immediate predecessors, these are thought to have reached the size of a male grizzly, but would, like Magericyon, have had more meat in their diet. Some was likely scavenged (since their teeth could crush bone), but much of it would have been actively hunted. They were never common, and did not make it to the end of the epoch.

Part of the reason that the bear-dogs suffered, and eventually vanished from Europe at this time (they survived for longer in Asia) may well have been the increasing competition from actual bears. Up until this time, European bears had been relatively small animals, with the very largest reaching the size of a modern black bear, and many somewhat smaller than that. Some of the early forms, such as Ursavus, managed to survive the crisis that wiped out so many other species, becoming progressively larger as they passed into the Late Miocene. But the slender, relatively fast-running, species, such as Hemicyon - the so-called dog-bears of the Middle Miocene - died out altogether.

Shortly before that happened, however, Ursavus was joined by a new kind of bear in the form of Indarctos. Most obviously, this new animal was a lot bigger, with the earliest species estimated to have weighed around 175 kg (385 lbs) - half again the weigh of the largest Ursavus, and somewhere between a black and a brown bear in modern terms. And the later ones were larger, eventually reaching almost the size of a modern Kodiak, the largest living subspecies of bear, at around 350 kg (770 lbs).

Indarctos was, like many bears (including, of course, the modern brown one) widely distributed across the Northern Hemisphere, being found from Texas and Arizona, as well as from Europe, Central Asia, and China. Exactly how it related to Ursavus isn't entirely clear, but the general consensus these days seems to be that it was actually an early panda, rather than belonging to some very early branch, as Ursavus does.

Unusually for a fossil species, we have evidence that male Indarctos possessed a particularly large penis. This is notable for a couple of reasons. For one, there's the fact that we know this at all; we can infer it from the length of its penis bone, but that's something that is rarely preserved in fossils, and so was quite an unusual find. Secondly, there's the fact that living pandas have a particularly small penis, by the standards of bears, which supports the idea from other evidence that Indarctos represents an early branch in panda evolution.

Sure, the rest of the animal was also larger than a panda, but, even taking that into account, the penis bone (and presumably the rest of the organ, although that's harder to know) was longer than we'd expect. Comparisons with other living species suggest that this may have been related to a mating system where females mate with a number of different males, perhaps due to a low population density where encounters were relatively rare. And that, once they did meet, the sex act itself may have been prolonged in comparison with living species.

Later still, once the Mediterranean had been closed off from the rest of the world's oceans, Indarctos was joined by Agriotherium, a heavily-built, short-faced, species with a strongly omnivorous diet. It too, was spread across the Northern Hemisphere, being found from sites as far apart as Nevada, Spain, and Myanmar. In fact, uniquely for a bear, it would even go so far as to enter sub-Saharan Africa. Somewhat closer to more typical bears than to pandas, it persisted in Europe well into the subsequent Pliocene epoch, a feat that Indarctos could not match.

The cooling worldwide climate, and the resulting drop in sea levels, had effects elsewhere in the world, too. Notably, it allowed dogs to leave North America for the first time. By the time this happened, however, the dogs had already undergone considerable evolution on their home continent. The first dog to reach Europe, therefore, Canis cipio, was already very similar to a modern jackal. Relatively little is known about it, but it was followed not much later by Eucyon, another small dog, which may be related to coyotes, and, at around the same time, the first European foxes and raccoon-dogs, also all-but indistinguishable from modern forms.

Significant though many of these changes were, though, the shift in the climate that heralded the start of the Late Miocene brought another change in the predatory fauna of Europe that was, perhaps, even more dramatic: the arrival of the first sabretooth cats on the continent...

[Photo by "Ghedoghedo", from Wikimedia Commons.]

1 comment:

  1. Really interesting. I've had a long day, working at spreadsheets. Reading about early mammals is wonderful. Thank you!