As the era of the dinosaurs drew to a close at the end of the Cretaceous period, about 65 million years ago, there was a relative absence of large predatory species on the planet. At this stage, the mammals which existed were small in size and mainly insectivorous in their feeding habits. Today's predatory groups, comprising the order Carnivora, had clearly started to emerge around 40 million years ago. The earliest origins of canids can be traced back to the late Eocene ear. Remains unearthed in North America from this period show that they were short-legged in appearance and more closely resembled mongooses and civets than present-day canids.
Hesperocyon, The Earliest Ancestor of Modern Canids
The earliest distinctive proto-canid, called Hesperocyon, had an alongated muzzle, a long tail, and a fairly slender body shape. Its legs were short, and it walked with a digitigrade action (on its toes). It was a true carnivore. Right from the dawn of their history, canids have been relatively unspecialized hunters. Hesperocyon, for example, not only hunted small mammals, but also almost certainly scavenged and ate vegetable matter, including fruit. It is not known whether they were social or solitary by nature, but since studies of contemporary canids suggest that hunting large prey is a major factor in the formation of packs, it seems likely that Hesperocyon was solitary, or may have lived in pairs.
Early Small Canid Species in North America
Towards the later part of the Oligocene, other small canids started to evolve in North America. But it was not until the close of the Eocene that canids began to spread further afield, to other continents.
The first canid which bore a clear resemblance to a modern member of the group was Cynodesmus. Its remains have been discovered in Nebrasks, it resembled coyote (Canis latrans) in appearance. Primitive canids were still evolved alongside Cynodesmus. Phalocyon, a contemporary genus also unearthed from early Miocene deposits in Nebraska, were probably rather similar to raccoons in appearance, and the structure of their limbs appears to have been more suited to climbing trees than running.
A third genus, Osteoborus, which first appeared somewhat later, during the late Miocene in the same part of the world, was primarily a scavenger rather than an active hunter. The origins of this group date back about 8 million years. They were stocky, heavily built dogs which filled an evolutionary niche similar to the hyenas of today.
Other members of this group, which were known as borophagines, may well have been more predatory in their lifestyle. There is evidence that Epicyon lived in groups and may have a lifestyle not unlike that of today's wolves.
At the close of Oligocene, the hesperocyonine dogs had developed into various forms. There were smaller canids, as Phaocyon and more powerful forms, such as Enhydrocyon, able to hunt and scavenge effectively, with teeth that enabled them to crush bones. The critical stage in the evolution of the canids occurred between 5 and 7 million years ago. At this time, before the continents had separated, the temperature in this part of the world was higher than it is today, but even so, these early canids would have needed a dense coat to protect them from the cold.
The dogs which first settled in Asia are thought to have looked something like Canis davisii animal the size of a coyote. This is considered to be the prototype that ultimately gave rise to the two main lineages of dogs recognized today, the foxes and the wolves.
Evolution of Early Dogs
The arrival of the early dogs to Asia occurred at an ideal time. Speed became more significant both for hunter and hunted alike, but by pursuing their quarry in packs, dogs were able to gain a vital advantage. The lifestyle of canids, which enables them to be omnivorous in their feeding habits, was probably a further factor which assisted their spread through Eurasia at this stage.
The slow-moving, well-protected mega-herbivores were gradually replaced by nimble animals, such as antelopes. In order to take advantage of such quarry, the lupine dogs developed pace, with the combined strength of the pack being able to overcome their prey. With individual dogs largely unable to inflict a fatal bite like cats, they were forced to rip their victims apart.
The success of their colonization of Eurasia can be gauged by the fact that canids had spread right across Europe by the early Pleistocene, some 3 million years ago.
Having undergone a period of development in Eurasia, some canids moved back across the Bering land bridge into North America, before the link was lost. This is why, for example, the gray wolf occurred throughout the northern hemisphere, with the earliest remains from North America dating back some 700,000 years.
The Pleistocene saw three different lineages of wolf in North America: Canis lupus and Canis rufus, both of which still survive here today, and the dire wolf which has become extinct.
Domestication of Dogs From Wild Canid Species
All domestic dogs have descended from the wolf (Canis lupus). Dogs have been in existence for at least 12,000 years, and probably much longer.
Origin and domestication of the dog
In ancient Egypt, the appearance of Sirius, the dog star, heralded the onset of the Nile flood that brought prosperity and life. The dog is the oldest domesticated species and has served man by herding flocks, guarding homes, hunting by sight and scent, retrieving wild animals, pulling sledges and simply by providing companionship. The dog was the only domesticated species populating both the Old and New World five centuries ago, when Europeans found the Americas. So, dogs either came to the Americas with humans from the Old World or they were domesticated independently in the Old and the New World. The phenotype variation in dogs led Charles Darwin to argue that different breeds had been independently domesticated from wild canid species on different continents, perhaps descending from wolf, coyote and several jackal species.