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The Origin of Dogs

[Excerpted from Science Corner]

As far as paleontologists can tell, the very first carnivorous mammals evolved during the late Cretaceous period, about 75 million years ago. However, it’s more likely that every carnivorous animal alive today can trace its ancestry back to Miacis, a slightly bigger, weasel-like creature that lived about 55 million years ago, or 10 million years after the dinosaurs went extinct.

The First Canids – Hesperocyon and the “Bone-Crushing Dogs”
Paleontologists agree that the late Eocene (about 40 to 35 million years ago) Hesperocyon was directly ancestral to all later canids–and thus to the genus Canis, which branched off from a subfamily of canids about six million years ago. This “western dog” was only about the size of a small fox, but its inner-ear structure was characteristic of later dogs, and there’s some evidence that it may have lived in communities, either high up in trees or in underground burrows. Hesperocyon is very well-represented in the fossil record; in fact, this was one of the most common mammals of prehistoric North America.

Another group of early canids were the borophagines, or “bone-crushing dogs,” equipped with powerful jaws and teeth suitable for scavenging the carcasses of mammalian megafauna. The largest, most dangerous borophagines were the 100-pound Borophagus and the even bigger Epicyon; other genera included the earlier Tomarctus and Aelurodon, which were more reasonably sized. We can’t say for sure, but there’s some evidence that these bone-crushing dogs (which were also restricted to North America) hunted or scavenged in packs, like modern hyenas.

The First True Dogs – Leptocyon, Eucyon and the Dire Wolf
Shortly after the appearance of Hesperocyon 40 million years ago, Leptocyon arrived on the scene. Leptocyon was the first true canine, although a small and unobtrusive one, not much bigger than Hesperocyon itself. The immediate descendant of Leptocyon, Eucyon, had the good fortune to live at a time when both Eurasia and South America were accessible from North America via land bridges. In North America, about six million years ago, populations of Eucyon evolved into the first members of the modern dog genus Canis, which spread to these other continents.

Although canines (including the first coyotes) continued to live in North America during the Pliocene epoch, the first plus-sized wolves evolved elsewhere. The most famous of these canines was the Dire Wolf, Canis diris, which evolved from an “old world” wolf that colonized both North and South America.

The end of the Pleistocene epoch witnessed the rise of human civilization around the world. As far as we can tell, the first domestication of the Gray Wolf occurred somewhere in Europe or Asia anywhere from 30,000 to 15,000 years ago. After 40 million years of evolution, the modern dog had finally made its debut!


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