Encyclopedia Largest prehistoric animals Vol.1 Vertebrates part1 Mammals ch.3 Carnivores - Canine,from the huge bear-dogs to dire wolf

The largest bear-dog was a species of Pseudocyon weighing around 773 kg, representing a very large individual

Pseudocyon, also known as Amphicyonopsis, is an extinct genus of terrestrialcarnivores belonging to the suborderCaniformia, family of Amphicyonidae ("bear dog") and which inhabited Euroasia and North America from the Miocene epoch to the Late Miocene subepoch living 23.3—7.2 Mya. Pseudocyon existed for approximately 5.3 million years.
With an upper weight estimate exceeding seven hundred and seventy kilograms, Pseudocyon was one of the largest of the bear dogs, quite probably even bigger than the largest known specimen of Amphicyon which was estimated to come from a six hundred kilogram individual. Additionally Pseudocyon also had a similar geographic distribution to Amphicyon although Pseudocyon does seem to have lived for slightly longer during the Miocene.
Pseudocyon was assigned to Amphicyoninae by Hunt in 1988 and to Amphicyonidae by Lartet (1851), Carroll (1988) and Pickford et al. in 2000. It is synonymous with Amphicyonopsis.
Specimens were located in Belomechetskaia Russian Federation, Santa Cruz, New Mexico, Pontigne and Malartic, a la ferme Larrieu, France, and Nebraska. The largest fossil find was of a mandible (F:AM 49247) founded in New Mexico. The mass estimate derived from the mandible was about 773 kg, representing a very large individual of Pseudocyon.



Very close contender is Amphicyon giganteus

Size: Up to 2.5 meters long. 1,4 meters tall at the shoulder.Weight estimated at up to  750 kg.
Amphicyon giganteus is an extinct species of Amphicyon, a large carnivorous bone cruhing mammal known as a Bear-Dog of the family Amphicyonidae, subfamily Amphicyoninae, from the Miocene endemic to Europe and Africa, living from 16.8—7.2 Ma existing approximately 9.7 million years An account of an ancient Rhinocerotidae (Iberotherium rexmanueli zbyszewskii) which may have been killed by a single individual or by a pack of Amphicyon giganteus in now what is Portugal, was written noted paleontologists Ginsberg et al. Amphicyon castellanus also shared its time period and habitat. Amphicyon giganteus was named by Kaup (1884). Amphicyon giganteus was the typical Bear-Dog Amphicyonid with morphology to both bears and dogs. Looking more like a bear than a dog, it had a large heavy tail, thick neck, robust limbs and teeth like a wolf. It was probably an omnivore with a lifestyle comparable to that of the brown bear


Amphicyon ingens is other very large bear-dog


Dimensions:length - 2,5 m, height - 120 сm, weight - 200-550 kg.
Amphicyon ("ambiguous dog") is an extinct genus of large carnivorous bone-crushing mammals, known as bear-dogs, of the family Amphicyonidae, subfamily Amphicyoninae, from the Aquitanian Epoch until the Tortonian. They ranged over North America, Europe, Asia, and Africa from 20.6—9 Ma ago, existing approximately 11.6 million years. Amphicyon was the typical bear-dog amphicyonid with morphology similar to both bears and dogs. With its robust build and maximum length of 2.5 m, the largest species looked more like a bear than a dog. It had a large heavy tail, thick neck, robust limbs and teeth like a wolf. It was probably an omnivore with a lifestyle comparable to that of the brown bear.
Amphicyon ingens lived from 20.06–13.6 Ma, approximately 6.46 million years. The species was originally described by W. Matthew in 1924 from specimens found in the Olcott Formation, Sioux County, Nebraska. Specimens attributed to this species have since been found in California, Colorado, and New Mexico. The largest known specimen to weigh 600 kg, making it the largest amphicyonid and one of the largest known carnivorous land mammals.

The largest canid of all time was Epicyon haydeni, which stood 37 inches tall (0.9 meters) at the shoulder.

Epicyon ("more than a dog") is a large, extinct, canidgenus of the subfamilyBorophaginae ("bone-crushing dogs"), native to North America. Epicyon existed for about 15 million years from the Hemingfordian age of the Early Miocene to the Hemphillian of the Late Miocene.
Epicyon was about 5 feet long, and its weight has been estimated at 150 pounds. Epicyon had a massive head and powerful jaws, giving its skull a lion-like shape rather than that of a wolf.
Epicyon was one of the last of the Borophaginae and shared its North American habitat with other canids:
Borophagus23.3 to 3.6million years ago (mya)
Epicyon from 20.6 to 5.330 mya
Carpocyon from 20.4 to 3.9 mya
Paratomarctus from 16.3 to 5.3 mya
Aelurodon from 15.97 to 5.332 mya
Canis lepophagus from 10.3 to 1.8 mya.Canis lepophagus may be the ancestor to the wolf.

The largest wolf is the dire wolf (Canis dirus) 1.5 m (4.9 ft) in length and weighed between 50 kg (110 lb) and 79 kg (174 lb).

The dire wolf (Canis dirus, "fearsome dog") is an extinctcarnivorousmammal of the genus Canis, roughly the size of the extant gray wolf, but with a heavier build. It evolved in North America and later moved into South America. Canis dirus is assigned to the Rancholabrean land mammal age of North America (240,000–10,000 years BP) and was among the many large carnivores and megaherbivores that became extinct in North and South America near the end of the Pleistoceneepoch. Salamander Cave in the Black Hills of South Dakota has produced the oldest known fossil of what is thought to be a dire wolf. The site preserves a fauna approximately 252,000 years old, based on uranium-series dating of a horse fossil found there. Its ending is associated with the Quaternary extinction event.

The dire wolf averaged about 1.5 m (5 ft) in length and weighed between 50 and 79 kg (110 and 174 lb), which made it the largest species in the genus Canis. Limb elements are rarely found outside the La Brea Tar Pits, which makes it hard to compare the size of average individuals between populations. The dire wolf is estimated to have been 8% shorter at the shoulder than the modern Northwestern wolf, and of equal height to the typical gray wolf, but more heavily built. With the exception of the canine teeth in some populations, male and female body and teeth sizes evidence no major sexual dimorphism, similar to most canines. In some populations, males’ canine teeth were considerably larger, suggesting male competition for breeding access. In other populations, lack of dimorphism in the canine teeth suggests little competition.
Despite superficial similarities to the gray wolf, the two species differed significantly. Today’s largest gray wolves would have been of similar size to an average dire wolf; the largest dire wolves would have been considerably larger than any modern gray wolf. The dire wolf is calculated to have weighed 25% more than living gray wolves.
Many of these characteristics were needed to fight off and prey on larger megafauna. The legs of the dire wolf were proportionally shorter and sturdier than those of the gray wolf, and its brain case was smaller than that of a similarly sized gray wolf.

The dire wolf"s teeth were similar to the gray wolf"s, only slightly larger, pointing to a hypercarnivorous to mesocarnivorous activity. The dietary characteristics were primarily carnivorous, as well as partially omnivorous. Other than size, there is no significant special adaptations in the mandibular corpus of the dire wolf to set it apart from the gray wolf.
Between C. lupus and C. dirus, C. lupus had a significantly greater mechanical advantage of the temporalis muscle over C. dirus at the lower carnassial and P4 (MATM1, MATP4).
The slicing teeth (P4, the carnassial) on the upper jaw of C. dirus are larger than those of the gray wolf, but those on the lower jaw are similar. The temporalis of the dire wolf could generate more force than seen in modern gray wolves, suggesting stronger killing bites.
Many paleontologists have proposed that the dire wolf may have used its relatively large teeth to crush bone, an idea supported by the frequency of large amounts of wear on the crowns of their fossilized teeth. The upper carnassial had much larger blade than that of the gray wolf, indicating greater slicing ability. It had a longer temporal fossa and broader zygomatic arches, indicating the presence of a large temporalis muscle capable of generating slightly more force than a gray wolf"s. However, other scientists have noted the dorsoventral and labiolingual force profiles are indistinguishable from those of other canids, such as coyotes and African wild dogs, indicating a similar diet.
Dire wolf teeth lacked the craniodental adaptations of habitual bonecrushers such as hyenas and borophagines. The dire wolf"s robust skull and susceptibility to tooth breakage suggests that it hunted for large prey or scavenged the carcasses of large prey. The dorsoventrally weak symphyseal region indicates it killed in a manner similar to its modern relatives, by delivering a series of shallow bites, strongly indicating pack hunting behaviour. However, the incidence of broken postcarnassial molars is much higher than in fossil gray wolves, indicating the species was probably less adapted to bone crushing than the gray wolf.

Dire wolves are part of the same carnivorous guild as the smaller gray wolves and coyotes.Dire wolves" overpowering bite, 129% of the force of the modern gray wolf, could hold and subdue their prey. As inferred from their large bodies and carnivorous teeth, they often took on large prey or megafauna, made possible by traveling in packs. Dire wolves were not specialized hunters—they fed on whatever megafauna was abundant.
Compared to modern species, a remarkable number of dire wolf specimens from the La Brea pits showed evidence of having broken their teeth in life. Specimens in the older part of the pit exhibited more tooth wear than those in the younger pit, which could be a result of either the older part of the pit containing more senior dire wolf specimens or a diet that included harder foods such as carcasses and bones.Another explanation for increased tooth wear and breakage could be intense competition among carnivores forcing C. dirus to eat as much of the carcass as quickly as possible.
The dire wolf has an extremely extensive fossil range. It is known to be located as far north as Canada and south into southern Bolivia. Ten localities in Mexico are known to contain Canis dirus: Cedazo, Aguascalientes; Comondu, Baja California; El Cedral, San Luis Potosн; El Tajo Quarry, Tequixquiac, and Valsequillo, all in Distrito Federal, Mexico; Lago de Chapala, Jalisco; Loltun Cave, Yucatбn; Potrecito, Sinaloa; and San Josecito Cave, Nuevo Leуn. The majority of these localities occur in the central and southeast-central portions of Mexico with few occurrences in the north or west. Of the central localities, San Josecito Cave and Cedazo have the greatest number of individuals of Canis dirus collected from a single locality; other localities in Mexico are known by only a few specimens.
Due to the large amount of remains at the Rancho La Brea tar pits it is possible dire wolves used animals trapped here as a food source and some end up being trapped and preserved themselves. It can also be concluded that they were social predators as they are most successful in defending carcasses.

The habitat of C. dirus varied considerably. In North America, it ranged from plains and grasslands to forested mountain areas. In South America, it occupied areas of arid savannah. The dire wolf lived in several habitats, tropical marsh with thorn-scrub to deciduous forest including some component of nearby grassland, and from sea level up to 2255 m (7400 feet). It was widespread, and its remains have been found in 136 places, from Alberta, Canada, to Tarija, Bolivia. Although the dire wolf was recorded as far north as Alberta, its remains have never been found at higher latitudes. The dire wolf may have migrated to northern Canada during interglacial periods, but its remains would likely have been obliterated by later glacial activity. However, the last named species of dire wolf was said to be found in North America stemming from Florida. The largest known dire wolves specimens have also said to have been recovered from this area of North America. So even though the dire wolf has migrated it may have found to be seasonal.
The dire wolf is well known for its unusually high representation in La Brea Tar Pits in California. Over 200,000 fragments representing more than 4,000 individual dire wolves have been recovered from the tar pits, more than any other mammal species. This large number suggests the dire wolf, like modern wolves and dogs, hunted in packs. The abundance of remains of the gray wolf (C. lupus, also known as C. furlongi) in the tar pits is about 1% that of the dire wolf.
The type specimen of the dire wolf was found in Evansville, Indiana, in the summer of 1854, when the Ohio River was quite low. The specimen, a fossilized jawbone, was obtained by Joseph Granville Norwood from an Evansville collector named Francis A. Linck.Norwood, who at that time was the first state geologist of Illinois, sent the specimen to Joseph Leidy at the Academy of Natural Sciences in Philadelphia.Leidy determined the specimen represented an extinct species of wolf and published a note to that effect in November 1854. In a publication dated 1858, Leidy assigned the name Canis dirus.
Norwood"s letters to Leidy are preserved along with the type specimen at the Academy of Natural Sciences, although one of the letters indicates the specimen was to be returned to Linck"s family, as Linck died in August 1854.

Whether the dire wolf originated in North America versus South America is the subject of controversy. Most paleontologists lean toward a North American origin for three reasons: first, more potential progenitors are present in the middle Pleistocene of North America; second, distribution of C. dirus is much better represented in North America, with 136 sites versus only three localities in South America; and last, C. dirus appears earlier in the fossil record in North America than South America. A North American origin implies that C. dirus migrated into South America from North and Central America. The dire wolves most likely migrated to South America via the Andean corridor, a proposed pathway for temperate mammals to migrate from Central to South America because of the favorable cool, dry and open habitats that characterized the region at times. This most likely happened during a glacial period, however, as the pathway then consisted of open, arid regions and savanna whereas during inter-glacial periods, it would have been characterized by tropical rain forest habitat.
The fossil record suggests that the genus Canis diverged from the small, foxlike Leptocyon in North America sometime in the Late Miocene epoch 9 to 10 million years (Ma) ago, along with two other genera, Urocyon, and Vulpes. Canids soon spread to Asia and Europe (8 Ma BP) and became the ancestors of modern wolves, jackals, foxes, and the raccoon dog.
By 3–5 Ma BP, canids had spread to Africa (Early Pliocene) and South America (Late Pliocene). Their invasion of South America as part of the Great American Interchange was enabled by the formation of the Isthmus of Panama 3 Ma ago.
Over the next nine million years, extensive development and diversification of the North American wolves took place by the Middle Pleistocene. Canis armbrusteri appeared, possibly from C. chihliensis in Asia. There is good evidence that the dire wolf evolved from C. armbrusteri, with the two taxa sharing in the open plains and grasslands of what is now the central United States.
C. dirus eventually displaced C. armbrusteri, with the latter"s final range shrinking to what is now the southeastern U.S., more specifically Florida. While this occurred, C. dirus expanded its range to include that of C. armbrusteri and moved into Central America and South America, appearing in the Late Pleistocene fossil record in northwestern South America.
Two subspecies of the dire wolf are known to have inhabited what is now the United States. C. dirus guildayi was smaller and ranged west of the Rocky Mountains. C. dirus dirus was larger and ranged east of the Rockies.
In 2010, a genetic study of extinct South American canids indicated that the South American Canis nehringi and Canis dirus were the same species, with the Gray wolf Canis lupus being in a sister clade.
Although it was closely related to the gray wolf and other sister species, C. dirus is not the direct ancestor of any modern species. Unlike the gray wolf, which is of Eurasian origin, the dire wolf evolved on the North American continent, along with the coyote. The dire wolf co-existed with the gray wolf in North America for about 100,000 years.

The dire wolf was one of the abundant Pleistocene megafauna—a wide variety of large mammals that lived during the Pleistocene. Approximately 10,000 years ago the dire wolf became extinct along with most other North American megafauna.
During the Late Pleistocene (300,000 years ago) the gray wolf (C. lupus) crossed into North America on the Bering Strait land bridge and competed with the dire wolf. Overlapping fossil findings of the extinct saber tooth cat, the Smilodon, shows that the dire wolf had these as competition in North America. Both species were social animals that hunt in packs and preyed on the same animals. Starting about 16,000 years ago, coinciding with the end of the last glacial period and the arrival of humans in North America, most of the large mammals upon which the dire wolf depended for prey began to die out, possibly as a result of climate and/or human-induced changes
Slower than the other wolf species on the continent at the time, like the gray wolf and red wolf, the dire wolf could not hunt the remaining swifter prey, and was forced to subsist on scavenging. By approximately 10,000 years ago, the large mammals and the dire wolf were extinct. Their demise, along with that of other large Pleistocene carnivores, was found to be related to the extinction of megafaunal prey.
More information is required in order to understand the extinction of C. dirus, including information on its biogeographical range, population size, competition, interactions with predators and prey, and its physical environment. Further discoveries about the dire wolf"s interactions with its competition and prey around the time of the extinction events would also be integral in understanding why C. dirus went extinct.

Encyclopedia Largest prehistoric animals Vol.1 Vertebrates part1 Mammals ch.3 Carnivores-Giant prehistoric bears,sequel

Cave bear- Ursus spelaeus



Ursus spelaeus, better known as the cave bear is by far one of the most common Pleistocene mammals in the fossil record, thanks mainly due to its behaviour of frequenting caves. In fact the fossils of Ursus spelaeus are so numerous that in World War I the German army used them as a source of phosphates.
The huge numbers of cave bear fossils in caves that have been documented to represent thousands of individuals to a single cave strongly suggests that this bear regularly spent time in caves, perhaps returning to rest after foraging. Bears that we know today by contrast only frequent caves during the hibernation period and sleep outdoors during the warmer months. The immense number of Ursus spelaeus fossils in certain caves has also led to the theory that these bears may have actually lived in social groups, although in depth study of the layers and dating has suggested that the remains are of single individual bears building up over the course of the Pleistocene period. As older remains became buried by sediment and fossilised they would have been of no nutritional value to anything and would have been left alone to accumulate, giving the impression of several bears living together rather than just one or two.
Cave bears have long been thought to be herbivorous animals, meaning that they only ate plants. Key evidence for this comes from the lack of premolar teeth that are usually absent in herbivores resulting in a gap between the forwards canines and rear molars called a diastema. Isotope analysis has also yielded low amounts of carbon-13 and nitrogen-15 which are usually found in high concentrations in carnivores. Counter to the strictly herbivorous diet theory however is the presence of some fossils that do have elevated levels of nitrogen-15, as, well as tooth wear associated with the gnawing of bones. Additionally some cave bear fossils also have tooth marks on them that seem to have been caused by others of their species. Not only does this suggest that cave bears occasionally ate meat, they may have scavenged the dead bodies of other cave bears that had died in caves. This is why Ursus spelaeus is today considered by most to have been an opportunistic omnivore that relied mostly upon eating plants, but would also supplement its diet with occasional meat when it was able to.
As one might expect cave bears were most common in areas that had large amounts of caves, particularly limestone that would have had caves carved out by water over several eons. As such cave bears lived in ecosystems that were between lowland plains and high level mountains that would have had a greater variety of trees and vegetation growing in them. Aside from offering a greater variety of food, a habitat preference such as this suggests that Ursus spelaeus did not compete with other European megafauna such as the woolly rhino and the woolly mammoth since they inhabited more open areas. Cave bears could also range across most of Europe, settling where they encountered suitable habitats, because the lower sea levels meant that marine boundaries such as the English Channel and North Sea did not exist.
A greater determining factor in the range of cave bears was the amount of glacial cover, something that would have expanded and receded over varying periods. Ursus spelaeus individuals from both milder and harsher times are known, with the individuals present in harsher times growing slightly larger than the bears that lived in slightly warmer times. This is a simple strategy where growing bigger creates a greater level of outer insulation while the total surface area of the body still increases but at proportionately less amount than the total body mass. This has been repeated and documented many times for different mammals that live in colder climates that all grow proportionately bigger that their closest related genera, perhaps the most relevant example here being the polar bear (Ursus maritimus) which does well in arctic conditions, but has been seen to overheat when kept in zoos in warmer climates.
Returning to the large collections of remains mentioned above, it’s clear that large numbers of Ursus spelaeus died in caves, but this needs further investigation. Because the remains of cave bears accumulated over tens of thousands of years it is easy to immediately discount the possibility of cave ins, as such an event would have only trapped one bear and then prevented others from entering. One widely accepted theory is that cave bears that did not eat enough food during the summer months to build up their fat reserves ended up starving to death as they slumbered. Even today animals that rely upon hibernation to last out the colder winter are vulnerable in times where plants do not grow or produce as much sustenance as they usually do, and back in the Pleistocene when ice sheets were toing and froing across Europe food would have been even more unpredictable from year to year.
More in depth study of some cave bear remains has revealed that bone disorders such as rickets, periostitus and osteomyelitis were quite common including other ailments such as the presence of tumours. Although not necessarily fatal to the individuals these bones belonged to, they would have impeded their ability to forage, slowly bringing the animal down to the point where it could no longer support itself. In these weakened states its thought that cave bears may have even fallen as prey to cave hyenas as well as even the European cave lion, that otherwise may have given a healthy bear in the prime of its life a wide birth.
Ultimately as a species, cave bears seem to have succumbed to the effects of habitat loss, as by only living in caves these bears would have only ever had a set amount of areas available to them. However as the Pleistocene was reaching its final stages, Neanderthals were beginning to become more common, and these primitive people also used caves for shelter. Inevitably one species would have to give way, and it was the cave bear that lost out to the greater numbers and intelligence of Neanderthals.
However despite the fact that they seem to have taken over, Neanderthals also seem to have held cave bears in very high regard. There are several burial sites in Europe where the remains of several bears have been assembled in pits and then covered with stone slabs. Perhaps the most famous site is Drachenloch, Switzerland where seven cave bear skulls are arranged to face the front of the cave, while six more are placed in recessed notches in the cave wall further in. Further remains were found bundled together, along with a skull of a three year old juvenile bear that had had its cheek pierced by the leg bone of another juvenile bear. Although some researchers claim that these are natural occurrences, there are a great many other who believe that remains like these are those of an ancient bear cult. How and why bears would be worshipped is uncertain, but it could be for anything from a totem animal, to a guardian of the caves against intruders, to maybe even a ward against other cave bears wandering in to Neanderthal settlements.



Ursus deningeri

Ursus deningeri (Deninger"s bear) is an extinct species of mammal of the family Ursidae (bears), endemic to Eurasia during the Pleistocene for approximately 1.7 million years, from ~1.8 Mya to 100,000 years ago. This large contemporary with the Cave Bear is reached sizes from 2.5 meters to length , 1.4 meters in height at the withers and weigh up to 600 kilograms.The range of this bear has been found to encompass both Europe and Asia, demonstrating the ability of the species to adapt to many Pleistocene environments. U. deningeri is a descendant of U. savini and an ancestor of U. spelaeus.
Ursus deningeri has a combination of primitive and derived characters that distinguishes it from all other Pleistocene bears. Its mandible is slender like that of living brown bears and Ursus etruscus. It also has derived characters of cave bears (Ursus spelaeus) and is considered to be the descendant of Ursus savini and very close to the common ancestor of brown bears.

Ursus ingressus

This large contemporary with the Cave Bear is reached sizes from 2.3 meters to length , 1.3 meters in height at the withers and weigh up to 350 kilograms.
Whereas U. spelaeus inhabited mainly low and medium elevation areas, U. ingressus has mostly been found in medium and high elevated regions . Recent isotopic analyses showed also some dietary differentiation between these cave bear haplogroups. Ursus ingressus was likely better adapted to continental environments and, thus, might have outperformed U. spelaeus during cold and arid climate conditions.
The vast majority of fossil remains in Late Pleistocene deposits from Niedźwiedzia Cave in Kletno, Sudetes, Poland, belong to the cave bear. Phylogenetic analyses based on a fragment of the mitochondrial D-loop region extracted from two cave bear samples unambiguously showed their close relationship with the Ursus ingressus haplogroup. This taxonomic affiliation of the cave bear remains from Niedźwiedzia Cave was further confirmed by biometrical analyses of molar teeth and skulls. Our results represent the first record of U. ingressus north of the Carpathian Arch, while radiocarbon dating (> 49,000 yr BP) of the samples indicates that they represent some of the oldest specimens of this cave bear taxon known so far. Multi-method phylogenetic analyses including numerous publicly available cave bear sequences allowed analysing the relationships among these samples in details, including the significance of particular clades, and discussing some aspects of cave bear phylogeography. The sequences of U. ingressus from Poland are most closely related to specimens from the Ural Mountains and next to Slovenia, which may indicate migrations between Central and Eastern European populations. The internal placement of Ural.  

Florida cave bear - Tremarctos floridanus



Tremarctos floridanus occasionally called the Florida spectacled bear, Florida cave bear, or rarely Florida short-faced bear, is an extinct species of bear in the familyUrsidae,subfamily Tremarctinae. T. floridanus was endemic to North America from the Pliocene to Holocene epoch (4.9 million — 11,000 years ago), existing for approximately 4.9 million years.Tremarctos floridanus.
This smaller contemporary giantess bears Arktodus and Arctotherium weighed up to 450-500 kg.
T. floridanus was widely distributed south of the continental ice sheet, along the Gulf Coast across through Florida and north to Tennessee, and across the southern United States to California.
Arctodus (3 million — 11,000 years ago) was a contemporary and shared its habitat with T. floridanus. The closest living relative of the Florida cave bear is the spectacled bear of South America; they are classified together with the huge short-faced bears in the subfamilyTremarctinae. They became extinct at the end of the last ice age, 10,000 years ago (possibly as late as 8,000 years ago at Devil"s Den in Florida), due to some combination of climate change and hunting by newly arrived Paleo-Indians.
 

Encyclopedia largest prehistoric animals Vol.1 Vertebrates part1 Mammals ch.3 Carnivores-Bears,fearsome giants atop the food chain on land
Attempted extended overview of the largest ever lived animals.Codex consists of collected and processed by me but written by other authors articles. Full overview of vertebrates including the latest paleontological finds. Because of the volume "ve split up. I begin with predatory mammals because these are my favorites.Individual parts are numbered according to their place in the full collection Proceedings in English in order to reach the maximum number of readers.And to preserve the style of the authors.

Опит за разширен обзор на най-големите,живели някога животни.Сборника се състои от събрани и обработени от мен,но написани от други автори статии.Пълен обзор на гръбначните животни,с включване най-новите палеонтологични находки.Заради обема съм го разделил на части.Започвам с хищните бозайници,защото това са моите фаворити.Отделните части са номерирани според мястото си в пълния сборник.

Bears




Arctotherium

The largest terrestrial carnivoran and the largest bear as well as the largest mammalian land-predator of all time was Arctotherium angustidens of the genus Arctotherium or the South American short-faced bears. A humerus of A. angustidens from Buenos Aires indicate that the big males of this species would have weighed 1,588- 1,749 kg and standing at least 11 feet (3.4 meters) tall on the hind-limbs.Arctotherium angustidens was a South-American Short Faced Bear from the genus Arctotherium. It was the largest Carnivoran that ever lived, in most regards; although male southern elephant seals can be heavier, they are semi-aquatic and covered in a layer of blubber.



A. angustidens was the largest Carnivoran that ever lived except that for southern and northern elephant seals. The northern elephant seal was 3,700 kg (8,200 lb) while the southern elephant seal was 5,000 kg (11,000 lb). It weighted about 983–2,042 kg (2,167–4,502 lb) but the authors said it was more likely 1,588 kg (3,501 lb) Arctotherium is an extinct genus of South American short-faced bears within Ursidae of the Pleistocene. Their ancestors migrated from North America to South America during the Great American Interchange, following the formation of the Isthmus of Panama during the late Pliocene. The oldest remains are from the Ensenadan epoch within the early-middle Pleistocene 1.2 Mya. Their closest relatives were the North American short-faced bears of genus Arctodus (A. pristinus and A. simus). The closest living relative would be the spectacled bear (Tremarctos ornatus)
Arctotherium was named by Hermann Burmeister in 1879. It was assigned to Tremarctinae by Krause et al. 2008. A specimen of A. angustidens from Buenos Aires shows an individual estimated, using the humerus, to weigh between 983 and 2,042 kg (2,167 and 4,502 lb), though the authors consider the upper limit as improbable and say that 1,588 kg (3,501 lb) is more likely. It is still possibly the largest bear ever found and contender for the largest carnivorous land mammal known to science. In contrast to their North American relatives, South American short-faced bears showed a trend of declining size and carnivory over time. This has been attributed to increased competition from other, later-arriving or evolving carnivorans, like jaguars, lions or Smilodon populator, following the early dispersal of short-faced bears to South America. (The North American carnivorans that invaded South America, including short-faced bears and Smilodon, quickly dominated the predatory niches formerly occupied by South America"s native metatheriansparassodont and avian phorusrhacid carnivores.)


North American short-faced bear (Arctodus simus)


The short-faced bear (Arctodus spp.) is an extinct bear that inhabited North America during the Pleistocene epoch from about 1.8 Mya until 11,000 years ago. It was the most common early North American bear and was most abundant in California. There are two recognized species: Arctodus pristinus and Arctodus simus, with the latter considered one of the largest known terrestrial mammalian carnivores.
The name short-faced bear derives from the shape of their skulls, which appear to have a proportionally short snout compared to other bears; this characteristic is also shared by its extant relatives, the spectacled bear and the grizzly bear. However, this apparent shortness is an optical illusion caused by their deep snouts and short nasal regions. The scientific name of the genus, Arctodus, derives from the Greek language and means "bear tooth".
The short-faced bear belongs to a group of bears known as the Tremarctinae, which appeared in the Americas during the earliest parts of the late Miocene epoch in the form of Plionarctos, a genus considered ancestral to Arctodus, Arctotherium and the modern spectacled bear (Tremarctos ornatus). Although the early history of Arctodus is poorly known, it evidently became widespread in North America by the Kansan age about 800,000 years ago.
Arctodus simus first appeared during the middle Pleistocene in North America, about 800,000 years ago, ranging from Alaska to Mississippi, and it became extinct about 11,600 years ago. Its fossils were first found in the Potter Creek Cave, Shasta County, California. It might have been the largest carnivorous land mammal that ever lived in North America. Only one Giant Short-faced Bear skeleton has been found in Indiana, unearthed south of Rochester on west of Nyona Lake on Chet Williams" farm. It has become well known in scientific circles because it was the biggest most-nearly complete skeleton of a giant short-faced bear found in America. The original bones are in the Field Museum, Chicago. The new Indiana State Museum, Indianapolis, and the Yukon Beringia Interpretive Centre, Whitehorse, Yukon Territory, Canada, have casts made of the bones. In a recent study, the mass of six specimens was estimated, one-third of them weighed about 900 kg (1 short ton), the largest being UVP 015 at 957 kg (2,110 lb), suggesting specimens that big were probably more common than previously thought. It stood 8–10 feet (2.4–3.0 m) tall on hind legs while a large specimen would have been 11–12 feet (3.4–3.7 m) tall with a 14 foot (4.3 m) vertical arm reach, and 5–6 feet (1.5–1.8 m) high at the shoulder when walking on all fours, it was tall enough to look a man in the eye. At Riverbluff Cave, Missouri, a series of claw marks up to 15 feet (4.57 m) high have been found along the cave wall indicating Short-faced bears over 12 feet (3.65 m) tall.
Arctodus pristinus inhabited more southerly areas, ranging from northern Texas to New Jersey in the east, Aguascalientes, Mexico to the southwest, and with large concentrations in Florida, the oldest from the Santa Fe River 1 site of Gilchrist County, Florida paleontological sites.
Researchers disagree on the diet of Arctodus. Analysis of their bones showed high concentrations of nitrogen-15, a stable nitrogen isotope accumulated by meat-eaters, with no evidence of ingestion of vegetation. Based on this evidence, A. simus was highly carnivorous and as an adult would have required 16 kg (35.3 lb) of flesh per day to survive.
One theory of its predatory habits envisages A. simus as a brutish predator that overwhelmed the large mammals of the Pleistocene with its great physical strength. However, despite being very large, its limbs were too gracile for such an attack strategy. Alternatively, long legs and speed (50–70 km/h (30–40 mph)) may have allowed it to run down Pleistocene herbivores, such as wild horses and saiga antelopes, in a cheetah-like fashion. However, in this scenario, the bear’s sheer physical mass would be a handicap. Arctodus skeletons do not articulate in a way that would have allowed for quick turns, an ability required of any predator that survives by killing agile prey. Paul Matheus, paleontologist at the University of Alaska Fairbanks, determined that Arctodus" moved in a pacing motion like a camel, horse, and modern bears, making it built more for endurance than for great speed. A. simus, according to these arguments, was ill-equipped to be an active predator, leading some to conclude that it was a kleptoparasite, using its enormous size to intimidate smaller predators, such as dire wolves, Smilodon, and American lions, from their kills.
Some authors also suggest that the giant short-faced bear and the cave bear were omnivores, like most modern bears, and the former may have eaten plants depending on availability.


Ursus maritimus tyrannus





Ursus maritimus tyrannus was a very large fossil subspecies of the polar bear that descended from an Arctic population of brown bears. Its name in Latin means Tyrant Sea Bear.
Ursus maritimus tyrannus was the first polar bear and evolved sometime in the mid-Pleistocene. While the oldest fossil is 100,000 years old, they are thought to have evolved between 100,000 and 250,000 years ago from a population of brown bears likely isolated by glaciation. That population is believed to have diminished in numbers quickly into a much smaller population selected by species individual variation who adapted better to the changed environment. Over time with intense selective pressures on a small population they evolved the characteristics of the first polar bears.
Initially the isolated brown bears were no different than the variations of brown bears of that time period. Because litters of cubs can show significant species variations in hair color and hair thickness, this gave certain individuals a survival advantage passed on each generation. Eventually skull changes and even changes in dentition occurred leading to the smooth and rather quick evolution of U. maritimus tyrannus.
U. maritimus tyrannus was considerably larger then its modern relative. If everything is scaled out correctly from its remains, it would had been 183 cm (6 ft) at the shoulders, 3,6 m (12 ft) long and would have weighted an average of 1.2 tons, making it the largest bear "and one of the largest mammalian carnivores to ever walk on land". Its tremendous size makes it even bigger than the other "largest" mammalian carnivores that ever lived, including Andrewsarchus, Agriotherium, and Arctodus simus. It"s speculated that this gigantic bear would, due to its formidable size and strength, have preyed on mammoths which also lived during the time


Agriotherium


Agriotherium size is approximately 2.7 meters long and up to around 650 kilograms.
Another thing to consider is that if Agriotherium was a scavenger then it was likely getting to carcasses after all of the choice pieces of meat had been consumed with perhaps only bones being left. This would probably not be enough to thwart Agriotherium from a meal however since the short snout, strong jaw closing muscles and robust construction of the skull and jaws were all the things that Agriotherium needed to develop massive bite force. Computer modelling in a 2012 study (see links below) confirmed that Agriotherium had one of the largest bite forces known amongst the members of the Carnivora (A group of mammals that includes dogs, bears, cats, pinnipeds etc which are specially adapted to exist by eating meat). By being able to crack open bones, Agriotherium could access and eat the bone marrow within, and for those not familiar, bone marrow is one of the most nutritious parts of an animal, and can last for several years after an animals death when encased inside of the bones. One of the better known bears in the worlds fossil record, the Agriotherium genus is also easily one of the largest currently known. With this large size it would be tempting to portray Agriotherium as a savage killers of any animal that might be unfortunate enough to be in its way, yet like with its more famous relative Arctodus (better known as the giant short faced bear) first impressions may in this case be deceptive. The post cranial skeleton of Agriotherium is that of a large but relatively underpowered animal that simply does not seem to have the skeletal framework necessary to cope with high stresses, such as those expected to be encountered while undergoing extreme physical exertion (i.e. catching and subduing struggling prey). The second clue is that Agriotherium has a proportionately short snout to that seen in many other bears. The advantages of having a short snout are simple, it means that whatever is being bitten, is closer to the point of jaw articulation (fulcrum) so that greater force can be brought to bear (no pun intended) against it.
These are all features that are common to Arctodus which also has isotopic analysis of its bones revealing that it was eating nearly every type of animal in its ecosystem, something very unusual for a predator, but common for a scavenger. Given the superficial similarity in form between Agriotherium and Arctodus, it’s reasonable to speculate that Agriotherium may have been a specialised scavenger, a theory that is becoming increasingly put forward for Arctodus. Again, the concept is very simple, by being bigger than any other predator on the land, Agriotherium could in effect bully the smaller predators away from their kills. This draws parallels in bear/wolf interaction that is observed in the wild even today, where grizzly bears will watch a pack of wolves bring down a prey animal, just to charge on in and drive them off after they have done all of the work for it. This fits with the surprisingly gracile skeleton of a large animal like Agriotherium, since if it was letting other predators do the work and the killing for it, why waste precious nutrients and calories upon developing and maintaining a skeleton stronger than it needed to be?
The idea of Agriotherium being what is termed a ‘hyper-carnivore’ is plausible, though it is not certain that Agriotherium only ate meat. Like with bears today, Agriotherium may have also supplemented its diet with fruits and certain plants, particularly tougher ones that required strong jaws. However the scavenger theory does actually fit better with Agriotherium in terms of the age of known fossils. Agriotherium first appears just after halfway through the Miocene before disappearing at the end of the Pliocene. The similar Arctodus however begins to appear in the Pliocene before becoming most numerous during the Pleistocene. It might be that Agriotherium was one of the first specialised scavenger bears but was eventually replaced in the worlds ecosystems by more advanced versions that form separate genera, as well as possibly other bone crunching animals such as hyena.