Good tidings and well-wishes!
Bears are actually very weird creatures. They’ve adopted a plantigrade stance, they’re heavily omnivorous carnivorans, and they’re easily the largest modern amniotes to engage in hibernation (though, it should be noted that many comparative physiologists maintain that the ursid variety of this behavior can be better described as “winter lethargy”). Even the way popular culture depicts them is eccentric: in many regions of North America, indigenous people live in fear of grizzlies (Ursus arctos horribilis) and/or black bears (Ursus americanus) while simultaneously cuddling and adoring their stuffed, manufactured counterparts.
So it should come as so surprise that the prehistoric relatives of these massive beasts were largely an odd lot, too. Of course, the most famous examples of bizarre ursid kinsmen are the famed ‘Bear Dogs’ (‘Amphicyonids‘) and the over-hyped giant short-faced bear (Arctodus simus), the latter of which will be discussed in greater detail later on. Another perfect, but little-known, participant in this trend is Agriotherium sp., a genus ranging from the Miocene to the Pleistocene in North America, Europe, Africa, and Asia.
Agriotherium has been historically considered a member of the Ursavini tribe: which includes and is named after Ursavus sp., the earliest known New World constituent of the Ursinae subfamily. The tribe is most easily recognized by their shared possession of small, simple anterior molars (which, in some species, are even further reduced), the relatively large fourth frontal premolars which were well-designed for shearing, and plantigrade stance (which distinguishes them from several earlier and contemporary groups of ursids such as the aforementioned ‘bear-dogs’). However, several recent authors have claimed that Agriotherium should instead be placed within the Ursinae itself.
As for the genus itself, in volume one of “The Evolution Of Tertiary Mammals In North America”, Robert Hunt writes that, among other features, “Agriotherium‘s outstanding traits are its anteriorly shortened lower jaw… [and] rudimentary [second metacarpal] talon.”
In “Ardipthecus Kadabba“, the authors explain “the possible presence of three phases of agriotheriine radiation during the Miocene. In the first phase, Indarctos arctoides was the only known species in Europe throughout the Vallesian… until it was replaced, in the second phase, by Indarctos atticus, a species that possibly arose from its predecessor. The third phase took place in the early Pliocene with the contemporaneous appearance of Agriotherium in Africa, Asia, and North America… [The] extinction of Indarctos atticus coincided with the proliferation of Agriotherium, and this may indicate a replacement of the former by the latter. However, it does not necessarily indicate an ancestor-descendant relationship, since Agriotherium was already highly diversified across continents towards the end of the Miocene…[It’s been] argued that an ancestor-descendant relationship between Indarctos and Agriotherium is merely based on stratigraphic occurence and not founded on synapomorphies. Based on [the] study of Agriotherium intermedium from China,… [some] have concluded that Agriotherium may have descended from a Hemicyon group. As a result, the origin and affinity of Agriotherium remains uncertain.”
Upon beholding the comparatively-lengthy limbs and strong dentition of the Agriotherium species, many authors have attempted to reconstruct this beast as a “hypercarnivore” which would have theoretically chased down ungulates and other land mammals to feed its disproportionately-high metabolic rate, as seen in the following illustration.
Arctodus has undergone similar treatment from the paleontological and artistic communities, having easily acquired more ‘super predator’ hype than any other fossilized ursid genus. However, Cameron McCormick of “Lord Geekington” has written an excellent article which explains why this “Godzillafication” of the short-faced bear is almost certainly a gross exaggeration, citing such reasons as its short canines, somewhat laterally-directed orbits, and a host of cranial features which closely resemble those of the largely herbivorous Tremarctos. Agriotherium has been similarly assumed to have been an insatiable, agressive, and powerful killer, yet it shares essentially all of the features which have forced the scientific community to disregard Arctodus as a creature befitting of this description. While both bears, in all likelihood, did consume meat in addition to foliage, it’s probable that this protein-rich fodder was generally acquired by way of scavenging rather than active hunting, but I have no intention of breaking open that particular can of worms by discussing this further.
May the fossil record continue to enchant us all!