Bears (Family Ursidae) are large, terrestrial mammals distributed widely across the Northern Hemisphere and parts of the Southern Hemisphere. Understanding their closest relatives requires examining their shared evolutionary history and taxonomic classification. This reveals connections to a diverse array of animals, from small weasels to massive marine mammals.
Defining the Carnivore Order
The broadest classification linking bears to their relatives is the Order Carnivora, a diverse group of placental mammals that share a common ancestor dating back approximately 55 million years. Despite the name, not all members subsist solely on meat, as many species, including most bears, have evolved into omnivores.
A defining anatomical feature of most carnivorans is the presence of specialized carnassial teeth. This dental arrangement involves the fourth upper premolar and the first lower molar, which work together with a scissor-like shearing action for processing flesh. The Order Carnivora is split into two major suborders: the Feliformia (“cat-like”) and the Caniformia (“dog-like”). Bears are firmly placed within the Caniformia suborder.
The Dog-Like Connection
Bears share the Caniformia suborder with several terrestrial families, all having diverged from a common ancestor known as Miacids. The ancestral line leading to modern bears (Ursidae) separated from the Canidae (dogs, wolves, foxes) lineage during the late Miocene Epoch, between 23 and 5.3 million years ago.
This closer relationship is evident in shared anatomical characteristics, such as the single-chambered structure of their auditory bullae. The Mustelidae family (weasels, badgers, otters, and ferrets) also shares this recent evolutionary history with bears. Additionally, members of the Procyonidae family, such as raccoons and coatis, are grouped within Caniformia. These three families—Canidae, Mustelidae, and Procyonidae—represent the core group of terrestrial mammals most closely related to bears.
Why Seals and Walruses Are Relatives
The most surprising relatives of bears are the Pinnipeds (seals, sea lions, and walruses), which are highly specialized for an aquatic existence. Pinnipeds are members of the Caniformia suborder, meaning their lineage shares a recent common ancestor with bears, dogs, and weasels. This evolutionary placement is widely accepted based on molecular and morphological evidence.
The aquatic families—Phocidae (true seals), Otariidae (eared seals), and Odobenidae (walrus)—evolved from a terrestrial caniform ancestor, shifting from land to sea. This adaptation led to a loss of the defining carnassial teeth function, as their diet of fish and marine invertebrates does not require shearing capability. Their flipper-like limbs and streamlined bodies represent a rapid divergence from the terrestrial body plan shared with bears.
The Cat-Like Branch
The other major suborder of Carnivora is Feliformia, which includes the families Felidae (cats), Hyaenidae (hyenas), Herpestidae (mongooses), and Viverridae (civets). While these animals are related to bears by being in the same Order, their evolutionary split is the most ancient within the group. The divergence between the Caniformia and Feliformia suborders occurred approximately 55 million years ago.
The anatomical difference in the auditory bullae is a distinction, as feliforms possess a double-chambered structure, unlike the single-chambered structure found in bears and their dog-like relatives. This early separation means that a leopard or a hyena is a much more distant cousin to a bear than a dog or a walrus.