Bear Evolution

[Roberto]

Recent news found by Brobear says that the largest cave bear (Ursus ingressus) has now been changed to (Ursus Kanivetz).

As with most prehistoric creatures in pop culture, they are typically shown as being wild, ravenous and savage bruins ubiquitous to a primeval world. Make no mistake - while any bear, especially one that grows to 400+kg, is a formidably well-armed and potentially very dangerous animal to humans, the evidence strongly suggests that cave bears were almost purely herbivorous. 


Ursus dolinensis, the Gran Dolina cave bear. This is the most basal cave bear species known, with morphological analyses showing a suite of primitive traits, placing this bear very close to the common ancestor with U. arctos. The original remains of this diminutive bear are known from the eponymous site of Grand Dolina in the Atapuerca mountains in Spain, though subsequent remains attributed to this species have also been found in Germany.[5] Dating at these sites puts the Grand Dolina cave bear at an age of about 1 million to 780,000 years ago, the Early Pleistocene. 

Ursus savini, the steppe cave bear. This species is considered as a sister species to U. deningeri. The steppe cave bear was first described in 1922 from middle Pleistocene deposits in Bacton, England, but fossil evidence has also led to the inclusion of some more recent cave bear taxa (previously thought to be closer allied to U. deningeri) as late subspecies of U. savini.[6] The far-flung locations of these subspecies suggest that the steppe cave bear had an Asian-Siberian origin, and their environmental context, as well that of the type locality, has led to its christened common name. Based on craniodental morphology, the authors of a new 2017 study have argued that it was well adapted to grazing (most other cave bears appear to have preferred boreal forest areas), and environmental data puts the bears in mosaic landscape settings of mixed woodland and steppe - hilly, but not mountainous.[6][7] Two subspecies of this bear are currently recognized:

Ursus savini nordostensis, the Beringian cave bear. The most northwestern cave bear know, found in Cherskiy, in the northeastern part of arctic Siberia, along the Kolyma river. The dating for its locality are very imprecise, ranging from between 0.5 and 1.5 million years.[2] The environmental settings in which it was found indicates steppe-tundra, with very few caves. While it inhabited what is technically known as Beringia, there is no evidence that it spread to North America. Based on its remains, it appears to be a relatively small bear, at about the size of a modern black bear. 

Ursus savini rossicus, the Krasnodar cave bear. Named after the type locality of Krasnodar, just north of the Russian Caucasus, the Krasnodar cave bear was found across the south of Siberia, as well as parts of Eastern Europe, including the Ukraine and as far west as Bulgaria,[6] and was a relatively small (but robust) bear, about the size of a modern black bear. In the past, it has been debated whether the Krasnodar cave bear should be considered its own species, or merely a subspecies of steppe cave bear on the basis of morphmetrics. For a while, aDNA evidence from remains from Kizel cave in the Urals placed the Krasnodar cave bear as a sister group to the Medvezhiya cave bear (see below..),[8] but these Uralian bears are now argued to be dwarf forms of the latter lineage.[6] The Krasnodar cave bear is known to have existed throughout the middle and late Pleistocene, with the most recent remains dating to about 28.9 thousand years ago 

Ursus deningeri, Deninger’s cave bear (the identity of the Deninger in question evades me). It lived between 1.8 million and 100 000 years ago (though that upper estimate seems questionable), and inhabited much of Europe, Anatolia,[8] and parts of the middle east. It is believed to be a sister lineage to the steppe cave bear and ancestral to the below cave bear species (or at least the U. spelaeus-kanivetz group), and possesses more primitive, less robust features than its more derived descendants,[10] being comparable in size to a modern brown bear. Isotopic testing and support the contention that this species was herbivorous, though some have argued for a more omnivorous diet based on dentition. 

Ursus kudarensis, the Kudaro cave bear. Formerly considered Ursus deningeri kudarensis, but now considered separate for reasons mentioned above. Still, aDNA suggests it split from the U. spelaeus-kanivetz group between 274,000 and 814,000 years ago.[15] It is named after the Kudaro caves in the Georgian Caucasus, a paleolithic site from which the first remains were found, as well as some Mousterian artifacts. It was a fairly large-bodied cave bear, larger than a modern brown bear and comparable in size to the classical cave bears of Western Europe. 

Ursus kanivetz, the Medvezhiya cave bear. The largest of the great cave bears, at up to 1.4m tall at the withers and weighing up to around 400–500kg.[27] It inhabited much of Eastern and Central Europe, the Urals, and, later on, parts of Western Europe. Until very recently, this bear bear was referred to as Ursus ingressus, or the Gamssulzen cave bear (indeed, Wikipedia’s recent article on this bear still refers to it by the old name), by Rabeder and Hofreiter (2004),[17] and almost all of the literature available will refer to this bear by this name. But aDNA analyses in 2016 revealed the type specimen to be a congener with cave bears from Medvezhiya cave in the Urals, once named U. kanivetz in 1973 by N. K. Vereshchagin.[18] Thus the older name has superseded the younger one. From the molecular data, we know that the Medvezhiya cave bear was a sister species U. spelaeus, with an estimated split date of 170,000–400,000 years ago. 

Ursus spelaeus, the western cave bear. Finally, we find our familiar Ursus spelaeus. The great cave bear of western Europe. A sister species to the Medvezhiya cave bear, they inhabited most of Western Europe and the Alpine region, but evidence shows that some small populations were more widespread than that. Even here, three subspecies have been recognized since 2004:

Ursus spelaeus ladinicus, the Conturines cave bear. One environment where cave bears weren't expected to be found was that of the high alps, especially during colder periods, since the flora at such high altitudes were thought to be unable to support such a large bear. Nonetheless, in the Alps, the remains of dwarf forms of U. spelaeus between 30-60kya over 2km a.s.l established their presence in the Italian Dolomites, at sites such as, yes, Conturines cave. This has led some scientists to conclude that the Dolomites were at least as warm as, if not warmer than, today.[22] In any case, the Conturines cave bear was a basal lineage within the western cave bears, and is known to have existed in the Italian Dolomites, as well as parts of nearby Slovenia, and aDNA shows that they were also found in southern France, at the Merveilleuse cave, and Belgium, at the Scladina cave.[23] This species was quite a bit smaller and more gracile than the larger, more familiar subspecies we’ll look at, at about the size of a black bear. 

Ursus spelaeus eremus, the Ramesch cave bear. Another alpine subspecies, found in and around the Alps, in what today comprises parts of Austria, Switzerland, Italy and southern Germany. Intriguingly, aDNA reveals the presence of this species at the Denisova and Strashnaya caves in the Siberian Altai - 7000 km east of their known center of distribution.[15] It is also from this subspecies that scientists first uncovered strong evidence for the distinction of the Western and Medvezhiya cave bears. Between 30,000 and 50,000 years ago, U. k. ingressus is known to have inhabited the Totes Gebirge region of the Austrian alps, occupying Gamssulzen cave. Less than 10km, a mere 2-hour walk apart (human standards, bears can move faster, I do believe), Ramesch cave was situated, and this is where Ramesch cave bears are known to have hibernated. Dating shows a period of overlap between the two bear lineages of about ~15,000 years. Yet we know from aDNA that there was no gene flow between the two caves, which remained both genetically and morphologically distinct.[25] Their separation has been more recently been compounded by isotopic analysis of their bone collagen, reflecting their diets when the two coexisted. By en large, the bears possessed two distinct (herbivorous) diets, with very little overlap. Using oxygen isotopes, scientists were able to determine that they may even have used different water sources as well, indicating that they may not have occupied the same landscape, either separated in space or in time due to climatic shifts.[26] This suggests that they had become reproductively isolated for long enough to undergo a full speciation - making the Ramesch-Gamssulzen divide a classic example of the separate species concept. If the names of the caves sound familiar, it’s because this study is what originally led to the naming of U. (k). ingressus and U. s. eremus, and their (initial) common names. 

Ursus spelaeus spelaeus, the classical cave bear. This is the species with which we are most familiar with. This subspecies was widespread in western Europe, from the Swabian Jura all the way west into the Iberian Peninsula. The earliest remains were named in 1794, from Zoolithen cave, which were later found to form a distinct genetic lineage withing the species.[29] It was a very large bear, the largest of the three subspecies, at up to 400kg or more,[28] and at around 1.3m tall at the withers, and a tad bit smaller than the Medvezhiya cave bear. These were the bears which were immortalized in the paleolithic art at Chauvet cave, and in the carvings at Geißenklösterle.[33] Interestingly, genetic studies analysing mtDNA of cave bears at cave sites in Spain, reveals strong evidence that cave bears returned to hibernate in the same caves in which they were born, which explains the distinct haplotypes in the Totes Gebirge.[30] The classical cave bear suffered a decline in genetic diversity towards the end of its lifetime. Finally, around, 32,000 years ago, a westward migration of Medvezhiya cave bears moved into the Swabian Jura, possibly due to worsening habitat conditions in eastern Europe. Unlike the case in the Totes Gebirge, they did not coexist, and instead the classical cave bears appear to have been outcompeted and replaced by their larger relatives.[31] However, more recent evidence suggests that these bears clung on for around 3,000 years later, as remains of this species dated to 28,730-28,500 years BP from southeastern France reveal. These bears still retained a similar diet to their earlier ancestors, suggesting they may not have had very flexible diets. Interestingly, these recent remains show evidence of human butchery. 

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