Aurorarctos

[brobear]

www.sciencedirect.com/science/article/pii/S258900422030420X 
 
In Carnivora, increases in body size often lead to dietary specialization toward hypercarnivory. Ursine bears (Tremarctos and Ursus), however, are the only omnivorous Carnivora that evolved large body sizes (i.e., >50 kg). Traits contributing to their gigantism, and how those traits evolved, have never been studied. Here we propose that special dental characters of Ursinae (parallel buccal and lingual ridges) permit a sagittally oriented mastication associated with increasing emphasis on plant foods. This pattern can be traced back to a new early diverging bear of plant-dominated omnivorous diet, Aurorarctos tirawa gen. et sp. nov. from the late Middle Miocene of North America, which was supported as the earliest known ursine bear by phylogenetic analysis. The anatomical transition to increased masticatory efficiency, probably together with the ability to hibernate, helped bears break prior ecological limitations on body size and led to the evolution of a distinctive lineage of herbivorous-omnivorous, large-bodied Carnivora.

[brobear]

it.wikipedia.org/wiki/Aurorarctos_tirawa

Aurorarctos tirawa is anextinct species of carnivorous mammal belonging to the ursidae . It lived in the Middle Miocene (about 15 - 12.5 million years ago) and its fossil remains have been found in North America .

This animal must have resembled a current bear , and the size was quite small; Aurorarctos is supposed to be the size of a present-day Malayan bear ( Ursus malayanus ), although the build was much more robust. Aurorarctos was endowed with a sturdy jaw and higher and higher towards the back. The premolar series was complete; the second to the fourth lower premolar had a double root. The mandible was devoid of premasseteric fossa or marginal process. The upper fourth premolar had no parastyle and protoconus, and the inner lobe was located in the anterior half of the tooth. The first molarthe upper one was endowed with a large posterolingual girdle similar to a cusp, while the second upper molar was endowed with a short heel, with a weak anteromedial accessory crest of the paracone and connected protoconus and metaconus. The lower fourth premolar had a lingual ridge and an undivided posterior ridge. The first lower molar had a protoconus with an anteriorly curved crest and a slightly sketched posterior crest; the entoconide was not subdivided. The lower second molar had a large trigonid and a separate paraconid.

Aurorarctos tirawa is considered to be the oldest member of the Ursinae , the subfamily comprising all current bears with the exception of the giant panda ( Ailuropoda melanoleuca ). Aurorarctos differed from slightly older or coeval animals such as Ballusia , Miomaci and Ursavus for some traits of the teeth which, instead, bring it closer to the genera Ursus and Tremarctos . Aurorarctos tirawa was first described in 2020 , based on fossil remains found in Cherry Countyin Nebraska ( USA ), in land dating back to the Middle Miocene.

The dental characters of Aurorarctos , as well as those of present-day bears, allow chewing on the sagittal plane; this type of chewing is correlated with an omnivorous diet with a particular predilection for vegetable food. Aurorarctos is supposed to have been the first bear to develop this type of dentition. According to the 2020 study, the anatomical transition to increased chewing efficiency, perhaps coupled with the ability to hibernate , may have helped bears overcome previous ecological limits regarding body size and may have led to the evolution of a distinct evolutionary line of carnivorous mammals with frankly herbivorous tendencies large size.

[OldGreenGrolar]

I like this bear already. Will do some research later.