Rubecula wrote: »
Not really expected to be found that far south I suppose, but as I think about it. Didn't the predators start to overlap each other after the continents collided?
I think big cats came north and I see no reason why the bear couldn't head south.
Galvasean wrote: »
The big cats expanded their range from north to south, Smilodon would be a popular example.
Few enough were innocent in the past, few enough are innocent in the present, we just don’t know why yet.
"At the time the giant bears lived there would have been lots of large herbivores (and) specialized predators like wolves, lions and sabre-tooth cats, but there would have been no specialized scavengers"
Adam Khor wrote: »
sounds like nonsense to me. What about all those vultures, condors and teratorns that are often and copiously found along with the remains of larger animals from those times? It takes minutes for a small flock of vultures to skeletonize a carcass, and only 10 of them are enough to intimidate a cheetah away from its kill. And some of these prehistoric vultures were the size of pterosaurs. I think they deserved a mention at the very least.
Dr. Leopoldo Soibelzon, researcher for the Museo de la Plata and CONICET, both Argentinian entities, commented that "it is a large bear of the species Arctotherium angustidens, of which the largest individuals could reach up to 4.5 m in a rearing position.
It was Soibelzon who presented the largest specimen known in 2011. Meanwhile, this new specimen, found in the San Pedro region, was identified as a young male who weighed about 800 kg at the time of his death and would've been 2.5 m rearing on its hind legs.
The giant bear expert noted that "the skull and mandible of this new San Pedro specimen are incredibly well preserved, and part of the pelvis, part of a humerus and radius, and six articulated vertebrae"
The beast's skull is really amazing regarding size and preservation state. It has fangs about 6 cm long, which are strong, sturdy and pointed and well designed to rend the flesh of its prey.
The lower jaw has 4.5 cm fangs, and the bear's molars too were well prepared to cut and crush the flesh and bone of its victim.
The largest Arctotherium angustidens would reach a size larger than the 2011 estimate, when Dr. Soibelzon announced the largest specimen. (...) had a strong tendency to feed on flesh and bone of animals they could hunt themselves, but also stole from other carnivores such as the sabertooth tiger.
Spores and grains of pollen from certain plants, fungi and algae have been found in the same sediments, which allows us to know that this giant bear lived in a steppe-like environment, with grassy vegetation, sand-like substrate, and always near water sources"
Dr. Soibelzon noted that these bears lived in the Pampas region until about 500.000 years ago. Meanwhile, bears as a whole arrived to South America about 3 million years ago when the Panama isthmus was elevated allowing land animals to arrive from North America"
The connection with forest habitats explains why U. arctos Pleistocene finds are rare in the north of Eastern Siberia, since open tundro-steppe and steppe landscapes dominated here.U. arctos Pleistocene remains are found on the territory of Yakutia since the beginning of the middle Pleistocene. It was assumed that at this time there existed a large bear close to U. a. kamiensis- at the end of the middle and beginning of the late Pleistocene the smaller U. a. priscus*, and at the end of the Pleistocene the latter was replaced by a small bear, U. arctos spp, similar in size to the modern Yakut brown bear.
In 2015–2016 in the north of Yakutia, new fossils of several specimens of exceptionally large brown bear have been found, which are described in this article.
All described finds belong to adult individuals, probably males. Their mineralization is insignificant and is characteristic of bone remains from the frost-holes of Yakutia during the Karginsky-Sartan period. The surface color of bones varies from yellowish light brown to dark brown. The mandibular branch of MM 1661 is more strongly mineralized, its color is dark brown, in places it is almost black, which is typical for bones of an earlier time, middle-beginning of the late Pleistocene.
The remains originate from the Upper Pleistocene sediments and are found together with the remains of typical mammals of the mammoth fauna, the woolly mammoth Mammuthus primigenius (Blum.), steppe bison Bison priscus (Boj.) and cave lion Panthera spelaea.
The brown bear fossils in many ways exceed the size of modern U. arctos from Yakutia. Among the new finds are CM1 and AN8004, the sizes of which are exceptionally large- the majority of their measurements are far superior to those of not only modern brown bears from Yakutia but also to the maximum sizes of the largest Eurasian subspecies, U. a. beringianus and U. a. piscator.U. arctos can reach extremely large sizes in the presence of a rich forage base. The modern Yakutia brown bear lives in harsh climactic conditions, and its diet is rather poor. It eats less animal food and low-calorie vegetable matter prevails in its diet. Under unfavorable conditions, an ecomorph of smaller bears came to be, characterized by an adaptive feature- a long winter sleep which lasts for 6.5 to 7.5 months.
It is difficult to explain the reasons for gigantism in the fossil brown bear of northern Yakutia. Probably it was due to the peculiarities of the Karginian warm period, which saw an increase in the diversity of vegetation, and accordingly, of edible plants. In addition, at this time (the bears would've had access to) the carcasses of large animals- like mammoths and woolly rhinos- and would've hunted their young.
In modern day U. arctos the tendency towards predation increases during periods of lack of vegetable food. The corpses of adult mammoths, which could weigh up to 4.000-5.000 kg, would provide a brown bear with high protein feed for a long time, since for example, a modern bear that feeds on a moose weighing up to 400-500 kg will take between 7 and 10 days to consume it fully.
The consumption of mammoth meat has been indicated by isotope analysis data from eastern Beringia. This increase in available food apparently caused the increase of size in the Karginian brown bears from Yakutia.
“If not for our arrival in Europe, I don’t see any reason why cave bears should not be around today,” says study coauthor Hervé Bocherens, a paleobiologist at the University of Tübingen in Germany who has studied cave bear remains for 30 years.
When the scientists ran their analysis, the data suggested that the cave bear decline started some 40,000 years ago—long before the last ice age set in. This also means that cave bears thrived throughout a number of earlier periods when temperatures significantly decreased. Instead, their downward trend starts right about the same time that our species began to spread across Europe.
“There is some evidence suggesting some modern humans may have set foot in Europe even earlier,” Bocherens says. “But as far as we know, they only really populated the continent around the time the cave bears start declining.”
The cave bear is one of the best known extinct large mammals that inhabited Europe during the “Ice Age,” becoming extinct ≈24,000 years ago along with other members of the Pleistocene megafauna. Long-standing hypotheses speculate that many cave bears died during their long hibernation periods, which were necessary to overcome the severe and prolonged winters of the Last Glacial. Here, we investigate how long hibernation periods in cave bears would have directly affected their feeding biomechanics using CT-based biomechanical simulations of skulls of cave and extant bears. Our results demonstrate that although large paranasal sinuses were necessary for, and consistent with, long hibernation periods, trade-offs in sinus-associated cranial biomechanical traits restricted cave bears to feed exclusively on low energetic vegetal resources during the predormancy period. This biomechanical trade-off constitutes a new key factor to mechanistically explain the demise of this dominant Pleistocene megafaunal species as a direct consequence of climate cooling.