The evolutionary history and systematics of the Carnivora are clouded in controversy, as the fossil record is patchy and incomplete. In spite of this limitation it is remarkable what paleontologists, evolutionary biologists and geneticists have managed to uncover in the way of the early history of mammals. A major breakthrough has been the development of accurate methods to date fossils.
About 65 million years ago (mya) the dinosaurs, which were the dominant animals on Earth, underwent a rapid and mass extinction. At this time the mammals were small shrew-
Meanwhile, placental mammals were evolving in the northern continents. Instead of their young developing in a pouch after being born, placental mammals grow their young inside them, in a womb. One of these placental mammals was a squirrel-
It is not known for sure why this replacement of Creodonts by Carnivora took place. The carnassial shear in the Carnivora was situated more to the front of the mouth than in the Creodonts. This meant that the teeth further back in the mouth could still be used for feeding on other foods, for example on vegetable matter. Perhaps the Carnivora could be more flexible in diet and therefore exploit more ecological niches, both meat eating and vegetable, than the Creodonts, who had no teeth behind their carnassial shear and so could only eat meat. Support for this idea comes from evidence of climatic change during the demise of the Creodonts. The earth became cooler and more seasonal. This may have led to a situation where prey became less available, but fruit crops and insects more abundant due to the seasonal bloom. The early Carnivora, known as miacids, were small and rather unspectacular, many resembling the genets of today. The major division into dog-
Traditionally Carnivora are divided on the basis of their anatomy and behavior into two suborders, terrestrial carnivores (Fissipedia) and marine carnivores (Pinnipedia). This subdivision is incorrect, for blood serum analyses have shown that the pinnipeds are closely related to bears and evolved from a single bear-