Unique Species and Useful Information for Roleplay (WIP)

Ursidae (True Bears.)
Arctodus (Short-Faced Bear)

Being one of the largest mammalian predators ever to walk the earth, it can be easy to think of the Short Faced Bear has a super-predator, able to take down nearly anything it wanted, especially since tests have revealed it to be a hyper carnivore. However this is only somewhat correct. While Arctodus could kill anything head on, it had trouble catching things as it's limbs were inefficient for fast acceleration and bearing the stresses put on the legs during a chase. Instead, Arctodus was likely a kleptoparasite, using it's extreme size to steal the kills of other predators. Arctodus moved in a pacing motion and with it's long legs, it would have had very good endurance that would have helped it cover lots of ground in search of a kill to steal. Once it began to feed the short jaws of Arctodus would have resulted in an incredibly strong bite force, capable of cracking open bones to feed on the nutritious bone marrow.

Ursus spelaeus (Cave Bear)

For a long time Ursus spelaeus, more commonly known as a Cave Bear, was thought to be exclusively a herbivore. However recent evidence suggests that they were opportunistic omnivores, feeding on berries, roots, and other flora, but also occasionally eating meat. How the Cave Bear acquired meat can be speculated. It may have ambushed prey animals it could have easily overpowered, scavenged abandoned kills, or like it's distant relative Arctodus, it may have occasionally been a kleptoparasite. (However it would not have been as well adapted for this like the Short faced bear is.) Like modern bears, the Cave Bear likely gained fat when food was plentiful, and hibernated during winter.

Hyaenidae
Crocuta crocuta spelaea (Cave Hyena)

Cave hyenas were predators and scavengers of the open plains much like their spotted African cousins are today. In fact, the Cave Hyena draws many similarities with African Hyenas. The females are usually larger then the males, and cave art shows that the Cave Hyena had a spotted coat just like African Hyenas. We also have a good idea of what the Cave Hyena ate. They preyed primarily on wild horses, followed by bison, and were even willing to go after dangerous Woolly Rhinos. There is also evidence of intraguild competition, in the form of wolf remains found in hyena den sites. An unusual aspect of it's behavior was that the Cave Hyena's likely ate these wolves. These Hyena's likely lived in clans similar to those of modern African Hyenas.

Pachycrocuta

While the Cave Hyena was large, Pachycrocuta was larger, in fact it's largest species may have been among the largest Hyenas that ever lived. Due to it's large size, Pachycrocuta was likely a small-pack hunter that hunted animals the size of a deer or larger. But if food was abundant enough, Pachycrocuta could have come together in Clans as big as those of modern Hyenas. Due to it's heavy set build, Pachycrocuta was not as good at chasing prey over long distances as other Hyenas. This may mean that it relied on scavenging more, or went after larger, not as fast prey.

Chasmaporthetes

Chasmaporthetes is one of the dog-like Hyenas, of which the Aardwolf is the only survivor. Unlike it's insectivorous relative however, Chasmaporthetes was likely a hyper carnivore. Uniquely, it had a very light build, with limb bones long and slender like a Cheetah. It cheek teeth were also slender and sharp edged like a cat. Chasmaporthetes was a very fast Hyena, and likely hunted like a cheetah, going after fast prey animals. There are 9 known species of Chasmaporthetes, with C. ossifragus being the only known species to cross the Bering Land Bridge into America.

Mesonychidae

Mesonyx

Mesonyx is a primitive predator, and seemed quite regular for one. That is for one thing. Uniquely, Mesonyx's toes ended in small hooves instead of claws. It also had a high sagittal crest that ran across the top of the skull. It would have allowed for the attachment of larger jaw closing muscles. This would then allow for the placement of larger jaw closing muscles that would in turn proportionately increase the bite force of Mesonyx. This would give Mesonyx a crushing bite allowing it to quickly kill smaller prey as well as hold on to larger animals that Mesonyx may have been able to weaken with successive bites.

Mongolestes

Dying out in the late Oligocene, Mongolestes is the last know and one of the most successful Mesonychids. A characteristic of Mongolestes that makes it different from other Mesonychids is it's dentition. These unique dental features include very large teeth, the loss of M3, and a mandibular symphysis that is steeper.

Harpagolestes

Harpagolestes was a hyena like, bear sized Mesonychid. But despite it's size, it's more likely that Harpagolestes was a scavenger. Features that support this are strong, curved canine teeth, a deep lower jaw, massive skull, and heavy wear on the molars. Along with stout limb bones it's unlikely Harpagolestes pursued it's prey. There are three species of Harpagolestes, and all of them have wear on the molars that suggest they regularly cracked bones with a powerful bite.

Viverridae
Viverra Lieakeyi (Giant Civet.)

An extinct species of Civet, Viverra is the largest known viverrid. The size of a small leopard, the Giant Civet was likely a strict carnivore due to it's dentition. In fact because of these two aspects, it's thought that the Giant Civet was an active predator.

Marsupial Mammals
Thylacoleo (Also known as the Marsupial Lion.)

Thylacoleo was a highly unique mammalian predator, with an array of tools that would have helped it survive in a hostile environment of predatory reptiles like Megalania, Quinkana, and Wonambi. One of these tools was the fact being a marsupial, Thylacoleo would have had a unique reproductive cycle, different from that of placental mammals. Another tool included it's highly specialized teeth. The upper and lower jaw incisors (front teeth) are greatly enlarged in a manner reminiscent of rodents. With it's immensely powerful jaw muscles it would have driven these teeth through critical locations such as the neck and spine. Thylacoleo had one of the strongest bites of all mammals, despite it's size. The marsupial lion also had a highly robust tail it would have used as a support help avoid being tipped backwards when wrestling prey or an enemy.
 

The third tools it had were it's forelimbs, unique for a marsupial due to the fact that the claws were fully retractable like a cat. Thylacoleo also had a partially opposable first ‘thumb’ digit that could have been used for extra grip. These adaptations along with an adaptation in the rear feet where the first toe was reduced but displayed a rough pad could have also been useful for climbing. Due to the fact it coexisted with stronger, deadlier predators like Megalania and Quinkana, it's very likely that Thylacoleo exhibited behaviors similar to a leopard. With it's many adaptations for climbing, Thylacoleo could haul it's kills up into the trees, out of reach of rival predators.

Thylacosmilus (The Sabertooth Marsupial.)

Like Thylacoleo, Thylacosmilus was also a unique predator. One of it's most unique characteristics were it's oversized saber teeth, that made it very similar to Smilodon, though it was not closely related to Saber toothed cats. A key difference is that Thylacosmilus was a marsupial (Mothers with young inside the pouch may have actually been capable of hunting, if the offspring were small enough.), and also that unlike Smilodon, it's saber teeth kept growing throughout it's entire life. If not worn down, they would keep growing larger. Similar to Eusmilus, the mandible had two large bone growths that ran alongside both teeth so they had extra support and protection when the jaw was closed. Due to being so similar to Smilodon, it's likely Thylacosmilus hunted in a similar way to Sabertooth cats, pouncing on prey and driving it's sabers into vulnerable areas.

Borhyaena

A marsupial of the Miocene, Borhyaena's incomplete remains has lead to confusion over how exactly it looked. Sometimes it is described as bear-like, but using length as a guide has led it to being described as more wolf-like. Usually depicted as being a cursorial (ground dwelling) predator that relied more upon ambush hunting when attacking prey. This behaviour has been inferred from study of the proportionately short legs that would have provided excellent acceleration to top running speed.

Thylacine (Also known as the Tasmanian Tiger/Wolf.)

Dukecynus

Arminiheringia

Creodonta
Hyaenodon

Although not as well known as some other mammalian predators, Hyaenodon was just as dangerous. The most interesting thing about Hyaenodon is it's dentition, as Hyaenodon would have relied on it's teeth a lot more than other predators. This is because they were it's only weapon along with it's sheer bulk. Like all creodonts, Hyaenodons limb structure limited leg movement to a vertical plane so they were unable to turn their wrists and forearms inward to trip, slash, or grab prey as modern carnivores can. Hyaenodons head looked too massive for it's head, but powerful muscles anchored it. Inside it's head were a set of dentition capable of shearing meat and crushing prey. An interesting aspect is that Hyaenodon had specially adapted slicing teeth at the back of it's jaws. The interesting thing about these teeth is that as the animal grew older these slicing teeth would rotate against each other. This constant grinding against each other meant that Hyaenodon maintained a cutting edge across these teeth for much longer than other carnivores and possibly had a longer life expectancy because of it.

Sarkastodon

Sarkastodon would have been a very large, powerful animal perfectly capable of killing most of the things it lived with. Like many other creodonts, Sarkastodon had robust canine teeth for seizing prey, and sharp pre-molars for slicing flesh. With this in mind it would seem that Sarkastodon was a hyper carnivore using its teeth to cut bite sized chunks of flesh and the strength of its jaws (amplified by the short muzzle that increased the efficiency of the muscles by holding bones nearer the fulcrum of the jaws) to crush bones.

Megistotherium

Megistotherium was one of the largest Creodonts. An intimidating beast, the skull of Megistotherium alone measured up to sixty-six centimeters long, almost as long as the average person’s arm and hand. It's likely that similar to modern day predators like Hyenas and Lions, Megistotherium would have hunted and scavenged, using it's large size to steal the kills of other predators.

Amphiyonidae (Bear Dogs)

Amphicyon

Amphicyon was one of the larger members of the Amphiyonidae, more commonly known as the Bear Dogs. There were many species of Amphicyon, and they all varied in size. Amphicyon major was as big as a Tiger, while Amphicyon Ingens would have been one of the largest mammalian predators to walk the earth. While size varied, they all had an immensely robust build that gave them the appearance of bears even though the heads were more dog-like. Amphicyon was extremely powerful, and could have wrestled many prey animals to the ground with it's well developed forelimbs. But this came at the price of speed, so Amphicyon may have gone after larger, slower prey animals then small and fast ones. There is currently one Amphicyon Ingens in this roleplay, played by me.

Daphoenus

Daphoenus was a smaller relative of Amphicyon, and like most primitive carnivores it was a plantigrade which meant that Daphoenus would have walked with the metatarsals in contact with the ground, giving Daphoenus a low walking ‘flat-footed’ appearance. Daphoenus skull displays a strongly developed sagittal crest (a ridge that runs along the back of the skull for the attachment of jaw closing muscles) which is thought to have allowed for considerably more powerful jaw muscles which in turn mean that Daphoenus had a very powerful bite.

Hemicyonidae (Dog Bears. (No, it's not the same as a Bear Dog.) )

Hemicyon

Hemicyon was a member of the Hemicyonidae, otherwise known as the Dog Bears. Not to be confused with the Bear dogs, Hemicyon was more closely related to Bears than dogs. But Hemicyon had a few big differences from true bears. First of all, it was a digitigrade instead of a plantigrade. What this means is that Hemicyon walked on it's toes, while bears walk with every part of the foot in contact with the ground. This adaptation would have made Hemicyon faster, and thus help it chase down prey. Another big difference from bears is that it's thought that Hemicyon was a hyper carnivore, and only ate meat.

Arctocyonidae

Arctocyon

There were many species of Arctocyon, ranging from jackal sized to bear sized. A primitive predator, Arctocyon was likely terrestrial, but may have also been able to climb trees. It's dentition suggests it was an omnivore, instead of a pure carnivore as it's teeth were not specialized for slicing meat. Arctocyon had short limbs and long heavy tails, this primitive anatomy suggests it was unable to run down prey. But with their powerful proportions, claws, and long canines, they may have been able to overpower smaller animals in surprise attacks

Entelodontidae (Hell Pigs.)

Entelodon

The type species of the family called the Entelodonts, Entelodon was a terrifying pig like creature. One of the largest Entelodonts, Entelodon may have been omnivorous like modern pigs, which would explain it's broad distribution across Eurasia, suggesting it was a successful species. It's large size and vicious jaws would have also helped Entelodon avoid predation. In fact Entelodon may have been a kleptoparasite like the short faced bear, finding and stealing kills from other predators.

Daeodon

The largest known North American species of Entelodont, Daeodon would truly had been a terrifying sight. It's ninety centimeter long skull is mostly jaw with two wide jugals (cheek bones). The wide jugals are thought to have allowed for the attachment of powerful biting muscles, giving Daeodon a powerful bite. However these jugals seemed to be larger in males, meaning they had a more powerful bite than females. This sexual dimorphism suggests males fought over females, the larger jugals helping them to bite harder, or make it harder for a rival to clamp their jaws around ones skull. 

Archaeotherium

One of the most best represented Entelodonts in the fossil record, Archaeotherium was an earlier and smaller member of the family. As with other entelodonts, Archaeotherium could open it's jaws extremely wide. While studies of the brain suggest it did not have a high level of reasoning, it had adaptations that gave it a sense of smell that would have been among the best in the animal kingdom, and good eyesight. Footprints found in a geological park show Archaeotherium running in a zig zag search pattern that would have helped it pick up scents better to find a meal.

Paraentelodon

 The largest known genus of entelodont in Asia, Paraentelodon was similar to Daeodon, and may have held a similar ecological Niche. As with other entelodonts, Paraentelodon had enlarged neural spines on its forward dorsal vertebrae that allowed support for more powerful neck muscles. This would have helped it hold up it's oversized skull, which like other entelodonts would have been capable of a powerful bite. Paraentelodon dentition was similar to other entelodonts. It had large canines at the front of the mouth would have been potent weapons that could have quite easily punctured a cranium. It is also likely that the forward canine teeth were used as tools for tearing off and picking up pieces of food that were then tossed to the back teeth with a flick of the head. Here the sharper premolars could cut and crush food into smaller pieces that allowed for more efficient digestion.