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It is associated with the formation of the mammoth steppe and continental glaciation. This was followed by an explosion of Canis evolution across Eurasia in the Early Pleistocene around 1.8 million YBP in what is commonly referred to as the wolf event. By 2.5 million years ago its range included the Nihewan Basin in Yangyuan County, Hebei, China and Kuruksay, Tadzhikistan. The large wolf-sized Canis appeared in the Middle Pliocene about 3 million years ago in the Yushe Basin, Shanxi Province, China. chihliensis appeared in northern China in the Mid-Pliocene around 4–3 million YBP. The position of the canids would change with the arrival of Canis to become a dominant predator across the Holarctic. The canids that had immigrated from North America to Eurasia – Eucyon, Vulpes, and Nyctereutes – were small to medium-sized predators during the Late Miocene and Early Pliocene but they were not the top predators.
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By 5 million YBP the larger Canis lepophagus appeared in the same region. In North America it gave rise to early Canis which first appeared in the Miocene (6 million YBP) in south-western US and Mexico. The jackal-sized Eucyon existed in North America from 10 million YBP and by the Early Pliocene about 6–5 million YBP the coyote-like Eucyon davisi invaded Eurasia. The caniforms included the fox-like genus Leptocyon whose various species existed from 34 million YBP before branching 11.9 million YBP into Vulpes (foxes) and Canini (canines). The first members of the dog family Canidae appeared 40 million years ago, of which only its subfamily the Caninae survives today in the form of the wolf-like and fox-like canines. The carnivoran ancestors of the dog-like caniforms and the cat-like feliforms began their separate evolutionary paths just after the end of the dinosaurs. Today, not all carnivorans are carnivores, such as the insect-eating Aardwolf.
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This dental arrangement has been modified by adaptation over the past 60 million years for diets composed of meat, for crushing vegetation, or for the loss of the carnassial function altogether as in seals, sea lions, and walruses. Carnivorans possess a common arrangement of teeth called carnassials, in which the first lower molar and the last upper premolar possess blade-like enamel crowns that act similar to a pair of shears for cutting meat. The name carnivoran is given to a member of the order Carnivora. The Cretaceous–Paleogene extinction event occurred 65 million years ago and brought an end to the dinosaurs and the appearance of the first carnivorans. Some observations are debated by researchers who do not always agree, and hypotheses that are supported by some authors are challenged by others. Researchers are limited to morphologic analysis but it is difficult to estimate the intra-species and inter-species variations and relationships that existed between specimens across time and place. The fossil record for ancient vertebrates is composed of rarely occurring fragments from which it is often impossible to obtain genetic material. However, the geographic origin of this radiation is not known.Ĭanis etruscus skull in the Montevarchi Paleontological Museum This implies that the original wolf populations were out-competed by a new type of wolf which replaced them. These analyses indicate a population bottleneck, followed by a rapid radiation from an ancestral population at a time during, or just after, the Last Glacial Maximum. This continuous presence contrasts with genomic analyses, which suggest that all modern wolves and dogs descend from a common ancestral wolf population that existed as recently as 20,000 years ago. The archaeological and paleontological records show grey wolf continuous presence for at least the last 300,000 years. This variation in sub-populations is closely linked to differences in habitat – precipitation, temperature, vegetation, and prey specialization – which affect cranio-dental plasticity. Studies of modern grey wolves have identified distinct sub-populations that live in close proximity to each other. The grey wolf Canis lupus is a highly adaptable species that is able to exist in a range of environments and which possesses a wide distribution across the Holarctic. The evolution of the wolf occurred over a geologic time scale of at least 300 thousand years. Illustration of a Pleistocene wolf cranium that was found in Kents Cavern, Torquay, England