led to the rapid evolution of swift-footed hunters such as dogs.

There were still 5 toes on each of Cynodesmus' feet, although the first toes were smaller than the rest. Its claws were narrow and partially retractable, like those of a cat, rather than the thick, blunt, weight-bearing structures that developed in later dogs. It was probably Cynodesmus' habit to ambush its prey, cat-style, rather than running it down, dog-style.

name: Cerdocyon time: Pleistocene locality: South America

(Argentina) size: 2 ft 6 in/80 cm long The dog family evolved in North America throughout the Tertiary period. The animals that belonged to this group could not reach South America because the 2 continents were separated by a sea. Then, toward the end of the Tertiary, in Pliocene times (about 5 million years ago), the Central American land bridge was reestablished, and animals could migrate southward. The dogs crossed into South America in the Early Pleistocene, some 2 million years ago, and the early fox Cerdocyon was among the invaders in this trek southward.

Two million years later, Cerdocyon lives on in the form of the common zorro or crab-eating fox, Cerdocyon thous, found from Colombia to northern Argentina. Crabs are only part of the diet of this omnivorous night-hunter. It also eats rats and mice, frogs and insects, fruit and carrion, and any creature's eggs it can find. Its Pleistocene relative probably pursued the same opportunistic lifestyle.

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