Toxodon was a genus of mammals native to South America during the Pliocene and Pleistocene. They had teeth that were specialized for tearing apart and eating the tough vegetation that populated the arid environment in which it lived. In many ways they were of similar build to a rhinoceros, though they are unrelated. Their skeletons are stout and heavy and show that they had a lot of muscle, particularly at the shoulders to support their large, powerful head.
Thylacoleo carnifex, known as the marsupial lion, is an extinct species of Diprotodontid that existed until 46,000 years ago. It is the largest meat eating mammal known to have existed in Australia, and the largest meat eating marsupial. Being a Diprotodontid, it is a relative of kangaroos, koalas, and wombats, making its predatory nature a rare occurrence in its order. One of the most remarkable things about T. carnifex was it’s teeth; instead of large canines as seen in most predatory mammals, it had dagger like incisor teeth. This incisors would have been ideal for piercing flesh, though it is unknown whether they served a more sophisticated purpose such as piercing major arteries to take down prey. It is my opinion that they did not, as a hole in the skull meant for the passage of nerve endings to and from their whiskers wasn’t very large compared to cats, who use their whiskers to aid in detecting where to bite vital areas, who have large holes, and dogs who don’t use their whiskers in such a way and have smaller holes. Even more astounding than the incisors, however, were the large premolars specialized for slicing flesh. Reduced to a single large tooth, it is one of the most specialized carnivorous features to have ever existed in the known world. Another feature of the animal was large, retractable claws, unknown in any other marsupial. They had partially opposable thumbs on the front and rear paws, and the thumbs in the front had much larger claws. It is thought that these “hands” would have allowed it to climb trees, and since it is known to have lived in unforested habitat, it may have dragged carcasses into the branches to keep them away from competitors in a similar fashion to leopards.
Really amazing, accurate, and realistic looking work. This artist really brings these ancient animals back to life.
Vulpavus was a genus of Miacid that existed 34 million years ago. It is a likely ancestor to all of the order Carnivora. Likely arboreal, Vulpavus would have hunted similarly to cats today— pretty much anything smaller than itself. This early arboreal lifestyle is important in regards to Carnivorans to come. In order to safely scale trees, Miacids had to evolve wrist bones that allowed them to rotate their paws. While most of Carnivora stick to the ground nowadays, this feature gave them an edge over their early competitors, the Creodonts. Creodonts could not move their wrists in such a fashion, and were limited to using their jaws for hunting (hence their large skulls) while the Carnivorans who moved in were given the opportunity for more varied hunting strategies. As commonly seen in arboreal animals and their descendants (just look at us!), Carnivorans also have larger brains. While Canids seem to have “reverted” back to the use of jaws for hunting, they are able to run more efficiently on their small paws, and their added brain power lets them make up for their smaller jaws through pack hunting (something Creodonts were much too dull for). Dogs who don’t hunt in packs tend to either take carrion or small prey like rabbits (compare prey selection of pack hunting wolves and solitary or pair hunting coyotes). Cats, however use their paws for hunting, which enables them to take down prey larger than themselves, even the solitary cats like tigers.
Amphicyon was a genus of carnivorans that lived until about 9 million years ago. Commonly known as “bear-dogs,” Amphicyon was a caniform that shared features with both dogs and bears, leading to some confusion to their placement. Traditionally, their family has been placed in Arctoidea— bears, raccoons, weasels, and seals— but recent evidence shows that they may instead be basal to Canids, or perhaps both, most likely being a sister clade to both groups. They would’ve been very bear-like in appearance, save for being a bit more lithe with a long tail. Like modern bears, they were likely omnivorous. With stout legs not suited for chasing, they likely would have been ambush predators like lions are today.
Hyaenodon was a genus of credonts (and thus not related to hyenas, despite the name, who are carnivorans) that existed from 42-16 million years ago, lasting for a whopping 26 million years. As typical of credonts, they had enormous heads with extremely powerful jaws and a bite force that far exceeds any modern carnivorous mammal’s to go with it. The genus was quite large, with 42 known species ranging in size from a small truck to a weasel, but most species were likely the apex predators in their respective environments for most of their history, with entelodonts (such as Archaeotherium) likely being the only real competitors they had. They lived all across the globe, save for South America, Australia, and Antarctica. Casts of their brain cavity show that they had a powerful sense of smell, and their nasal cavity extended much further into the back of the throat than in most animals, which gave them the ability to cram a lot more food into their mouth and likely allowed them to clean a carcass more quickly. Recently, comparisons have been drawn with modern animals of similar builds and it is believe they could have ran as fast as 35 miles an hour— fast enough to catch one of their most beloved prey items, Mesohippus. Due to their low lying bodies, it is believed that Hyaenodonts were ambush predators, using the brush as their ally. As their environments got drier, and vegetation more scarce, the fossil record has actually been able to show us that they moved to the more verdant watering holes to hunt, waiting for animals to drink. The mass quantities of bones founds at such locations with Hyaenodont wounds show that this was a very prolific hunting strategy.
Despite all these apparent advantages, they had important disadvantages that proved to be their downfall with the arrival of carnivorans as competitors (notably Amphicyon). For one, they had significantly smaller brains incapable of forethought and cooperation, so carnivorans tendency to pack hunt put all creodonts at a deep disadvantage. Furthermore, their wrists didn’t have the appropriate structure required for rotation— the paws could only move forward and back. Carnivorans, however, are able to move their wrists and use them grab and manipulate prey, where as creodonts like Hyaenodon could only use their jaws (one reason for their massive size and bite force, a feature that would be unnecessary in carnivorans). This gave Hyaenodon significantly fewer hunting strategies, allowing Carnivora to dominate the niche.
Indohyus was an artiodactyl from Asia. When a technician working on an Indohyus research project accidentally broke a skull, a professor recognized that the auditory bullae was shaped very unusually, and resembled only those of whales and the earlier Pakicetus, long believe to be related to whales. This discovery marked Indohyus as the potential “missing link” between land-dwelling artiodactyls and cetaceans. The bones of Indohyus have a thick outer coating that makes them heavier, and combats buoyancy, allowing them to stay submerged in water. It was only about the size of a raccoon or house cat, so it’s believed that it lived a semi-aquatic lifestyle similar to that of the water chevrotain. Chevrotains dive underwater for up to four minutes in order to avoid predators, usually birds of prey.
Sivatherium was a genus of giraffids that had large, elaborate ossicones that have given it comparisons to modern day moose. Unlike bone derived antlers, however, the ossicones of giraffids are made from ossified cartilage and not bone, and retain the fur and skin covering, where as deer shed their velvet. Sivatheres lived throughout Africa and southeastern Asia, and may have lived as recently as 8000 years ago, as evidenced by rock paintings that seem to depict a very similar creature. It would have looked like a very large okapi (around seven feet tall at the shoulder). Interestingly, throughout most of its scientific history, there has been a heated debate: did it have a trunk?
The first skull depicted is that of modern giraffes, and the center is Sivatherium. The final skull is a tapir’s, a modern day animal with a trunk. When all three skulls are compared, one can see why scientists think Sivatherium could have had a trunk. It is the writer’s opinion, however, that Sivatherium did not. The likelihood is that Sivatherium instead had perhaps a sort of inflated, fleshy nose, as depicted by this reconstruction:
Such a nose would likely be used for amplifying calls, perhaps especially during mating season, or even be inflated for a warning or mating display. It is also likely that such a nose would aid the animal in cooling itself in the hot climate it evolved in. If both uses were true, the nose may have even had a bright, colorful display when inflated and filled with blood. In this scenario, they would also likely have had highly flexible lips that would aid in browsing.
Archaeotherium was a genus of artiodactyls in the family Entelodontidae of the suborder Suina, making them relatives of modern day pigs. Archaeotheres, unlike their better-known cousins, were predators. The bones of other mammals, including the jaws of rhinoceros ancestors, have been found with marks that match the fangs of these giant swines. Evidence also shows that, similar to leopards of today, they kept stashes of food hidden away from potential thieves. A fossil trackway even shows the tracks of a Subhyracodon stopping to see an Archaeothere approach, and then falling into a gallop with Archaeotherium’s tracks in pursuit. They had large neck muscles to support a heavy head, and large olfactory lobes which suggests they had a strong sense of smell. Large predators, they stood at about 1.2 meters at the shoulder and were 2 meters long. Despite being apex predators, it is believed that in times when prey was scarce, Archaeotherium would eat roots and tubers much like modern day pigs.
