PLATE 1

A scene in North America during the late Eocene

An adult Hesperocyon gregarius watches over her two pups in front of their den, in a forest environment.

PLATE 2

Life reconstruction of Enhydrocyon

A large hesperocyonine of the genus Enhydrocyon, from the late Oligocene to the early Miocene (Arikareean) of North America, uses its strong premolars to crush the bone of an ungulate.

PLATE 3

Life reconstruction of Osbornodon fricki

Osbornodon fricki, from the early Miocene (Hemingfordian) of North America, was the largest member of the subfamily Hesperocyoninae, reaching the size of a small wolf.

PLATE 4 (FACING PAGE)

A scene in western North America during the Miocene (Barstovian)

A pack of the wolf-size borophagine Aelurodon ferox is in pursuit of a three-toed horse of the genus Neohipparion.

PLATE 5

Life reconstruction of Borophagus secundus

The large Borophagus secundus, from the late Miocene (Hemphillian) of North America, was an advanced borophagine that showed the most extreme adaptations for bone crushing in its strong skull and robust premolars.

PLATE 6

A scene in North America during the late Miocene (Hemphillian)

In an environment of grassland and forest patches, a young adult Eucyon davisi approaches one of its parents in a submissive attitude. It is possible that such youngsters remained in their parents’ territory and helped raise pups, which is the origin of larger social groupings in several species of the subfamily Caninae. Two antilocaprine antelopes of the genus Texoceros watch the jackal-size canids from behind the fallen tree.

PLATE 7

A scene in North America during the Pliocene (Blancan)

In this mosaic of grassland and woodland, a solitary adult Borophagus diversidens tries to defend its prey, the camelid Hemiauchenia, from a pack of Canis lepophagus. Facing only one member of this last species of borophagine would be the only chance for the smaller canids to appropriate a carcass. If B. diversidens had the help of other members of its species, the coyote-like C. lepophagus could only wait until the larger dogs had gorged themselves to satisfaction.

PLATE 8

A scene in western North America during the late Pleistocene (Rancholabrean)

An adult dire wolf (Canis dirus) calls for its pack while a herd of Columbian mammoths (Mammuthus columbi) ambles past in the background.