Arctocyonidae, if monophyletic, was a morphologically disparate lineage. Some genera, such as
Chriacus, were fairly small, and bore adaptations for an
arboreal or
scansorial lifestyle. Others, like
Anacodon, were very large and robust, having adaptations for both arboreal and fossorial lifestyles.
Arctocyon, particularly
A. mumak, appears to have been the most terrestrial, though likely descended from arboreal ancestors. The
zygomatic arch of
Arctocyon specifically was very large, with a posterior angle anterior to the
mandibular fossa, almost forming a right angle. In most genera, the
incisors were small and unspecialised, though others, like
Thryptacodon, had modified them into
grooming teeth convergent with those of
lemurs. Though the canines likely had a role in feeding in certain genera, In the case of
Arctocyon, the lower canines were longest, to the extent that they were accommodated by a gap (or
diastema) between the upper canines and
premolars. The cheek teeth were
tricuspid (three-cusped) and were often
bunodont. The premolars were simple, if fairly sharp, Overall, the dental morphology of arctocyonids suggests that they were omnivorous to varying degrees.
Postcranial elements In
Arctocyon, the mammillary processes of the dorsal vertebrae were robust (suggesting powerful musculature), and the
caudal vertebrae appear to have been tightly interlocked, suggesting that the tail was fairly rigid. In
Chriacus, however, there are signs that the tail may have been prehensile. Arctocyonid limbs were fairly typical in length, with stout
ulnar and
fibular shafts. In
Anacodon, particularly, the limbs were very robust. In
Chriacus, the ankle joints were flexible and allowed the hind feet to rotate, enabling them to climb downward.
Anacodon's ankles had very little lateral movement. Five digits were present on all limbs. The
phalanges were narrow and long, though the innermost and outermost digits were slightly reduced. In the case of
Chriacus, the innermost digit (the hallux) was divergent. On all digits, the
unguals were laterally compressed and quite clawlike. In some genera, like
Anacodon, they may have been used for digging. == Biology ==