Paleontologists in the United States have identified a new genus and species of early arctoid from an exquisitely preserved skeleton found in North Dakota’s Brule Formation.
Life reconstruction of the extinct bear-dog Amphicyon ingens, a very distant relative of Eoarctos vorax. Image credit: Roman Uchytel.
Eoarctos vorax lived in what is now the United States approximately 32 million years ago (Early Oligocene epoch).
A nearly complete skull and skeleton, plus several additional jaw fragments, of the species were found at the locality of Fitterer Ranch in the Brule Formation, southwestern North Dakota.
Eoarctos vorax belongs to Subparictidae, a North American family of extinct bear-like carnivorans within the infraorder Arctoidea.
“Arctoidea is the most diverse clade in the order Carnivora, with approximately 268 extinct and living genera, about 55% of all carnivorans,” Dr. Xiaoming Wang, a vertebrate paleontology curator at the Natural History Museum of Los Angeles, and colleagues wrote in their paper.
“It includes such familiar, often iconic, predators as bears, seals, sea lions, and walrus, red pandas, skunks, raccoons and ringtails, weasels, otters, and badgers, as well as a large group of extinct bear dogs (Amphicyonidae).”
“Arctoidea, together with its sister group, infraorder Cynoidea (mostly the dog family Canidae), forms the suborder Caniformia, or the dog-like carnivorans.”
“The caniforms, in turn, form the largest clade of Carnivora and are sisters to suborder Feliformia, the cat-like carnivorans.”
“Arctoids, unsurprisingly, also occupy the widest ecological spectrum known to carnivorans, ranging in body sizes from the largest (elephant seal, over 3 tons) to the smallest (least weasel, less than 60 g), spanning five orders of magnitude, and in trophic adaptations, from top predators (polar bear) to omnivores (raccoon and badger) and even obligatory herbivores (giant and red pandas).”
“With this unparalleled diversity, the evolutionary history of the arctoids is understandably complex, and often masked by convergences of morphological adaptations,” they wrote.
“As a result, a clear understanding of the phylogenetic relationships among these clades is still lacking.”
Eoarctos vorax was mainly a solitary predator with racoon-like proportions and a body mass of around 4.3 kg.
The animal also had cat-like claws that likely helped it climb up and down the trees of the ancient wetland.
It may have preferred wooded areas with extensive canopy coverage but was capable of traveling in the savanna peripheries as well. It mostly foraged on the ground, possibly preferring riparian habitats.
“Eoarctos vorax had a plantigrade standing posture and scansorial mode of locomotion, capable of long-distance travel on the ground,” the paleontologists wrote.
“It lacked a prehensile tail and was unlikely to perform hindfoot reversal.”
“Lacking powerful proximal limbs and a flexible vertebral column, it possessed no specializations toward a semiaquatic or semifossorial locomotion.”
“We consider similar-sized living arctoids, such as raccoon (Procyon lotor), fisher (Pekania pennanti), tayra (Eira barbara), and lesser grison (Galictis cuja), close ecological analogs for Eoarctos vorax.”
Eoarctos vorax’s shell-crushing teeth further suggest that large-sized, thick-shelled freshwater mollusks formed its main diet, possibly supplemented by fruits and carrion.
“To specialize on hard-shelled mollusks, it may have needed to walk along stream banks for long distances during foraging and possibly wading into shallow water to acquire gastropods,” the researchers wrote.
“It may have been a fearless hunter, like badgers and wolverines, when confronting an adversary or defending its home range.”
“Eoarctos vorax thus stands out as the first durophagous arctoid, possibly the first known molluscivore, among Carnivora.”
The paper was published in the Journal of Vertebrate Paleontology.
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Xiaoming Wang et al. An exquisitely preserved skeleton of Eoarctos vorax (nov. gen. et sp.) from Fitterer Ranch, North Dakota (early Oligocene) and systematics and phylogeny of North American early arctoids (Carnivora, Caniformia). Journal of Vertebrate Paleontology 42, sup1: 1-123; doi: 10.1080/02724634.2022.2145900
