The earliest members of the bear family belong to the extinct subfamily Amphicynodontinae, including Parictis and Allocyon. These animals lived during the late Eocene to early middle Miocene, roughly 38 million years ago in North America. They looked very different from modern bears, appearing small and raccoon-like with diets similar to badgers. A slightly younger species called Allocyon appeared in the early Oligocene between 34 and 30 million years ago. European genera like Amphicticeps and Amphicynodon emerged around the same time as Allocyon. These ancient creatures were semi-aquatic and otter-like, sharing morphological traits with pinnipeds. The Bering land bridge may have allowed faunal exchange across continents as early as 37 million years ago. Later, the raccoon-sized Cephalogale became the oldest-known member of the Hemicyoninae subfamily about 30 million years ago in Eurasia. This group included Phoberocyon and Plithocyon which existed between 20 and 7 million years ago. A Cephalogale-like species gave rise to Ursavus during the early Oligocene. This genus proliferated into many species in Asia and is ancestral to all living bears. Members of the living lineages diverged from Ursavus between 15 and 20 million years ago. Genetic data suggests the giant panda lineage split first around 19 million years ago.
Anatomy And Physical Adaptations
Bears are generally bulky and robust animals with short tails and stocky legs. They are plantigrade, meaning they distribute their weight toward the hind feet when walking. This gait makes them look lumbering but allows for bursts of speed before tiring. Their shoulder blades and pelvis are massive to support their bulk. Strong forelimbs catch prey, excavate dens, dig out burrowing animals, and club large creatures. Unlike most other land carnivorans, bears have non-retractable claws used for digging, climbing, tearing, and catching prey. The front paws are flexible enough to grasp fruit and leaves. Pandas possess a unique bony extension on the wrist that acts as a thumb for gripping bamboo shoots. Most mammals have agouti hair with bands of color, but bear hairs have a single color throughout their length. Polar bears have hollow, translucent guard hairs that gain heat from the sun and conduct it to dark-colored skin below. They also have a thick layer of blubber for extra insulation. Bears have small rounded ears to minimize heat loss. They lack touch-sensitive whiskers on the muzzle but possess an excellent sense of smell better than that of dogs. Their skulls are massive providing anchorage for powerful jaw muscles. The canine teeth are large but mostly used for display while molar teeth are flat and crushing.