Evolution and systematics

The earliest fossil corvid, a jay-like "crow" was found in France and dates to the middle Miocene period (about 17 million years ago). The large number of species endemic to eastern Asia (36) and the New World (29) however, suggest that the family may have originated in the Far East, and taken alternative routes a very long time ago.

The ancestors of New World jays spread to the Americas, but no other corvids besides jays are found in South America. Marzluff and Balda conclude that the other genera were relatively recent arrivals in North America—the Bering land bridge that formed between Asia and North America allowed the Old World genera Corvus, Perisoreus, Pica, and Nucifraga to cross continents. Scientists are unclear why so few corvid species occur in Africa. The two monotypic genera have features which suggest an ancient origin: most strikingly, the Stresemann's bush-crow (Zavattariornis stresemanni), found only in southwest Ethiopia, is shaped like a ground-jay, colored like a nutcracker, and builds a nest like a magpie. Madge speculates that this species may be a relict population of an ancient ancestor to a number of genera.

Taxonomically, the corvids, consisting of 26 genera and 123 species, have fitted historically within the family Corvidae. DNA reclassification work has not changed this essential grouping. Sibley and Ahlquist (1990) widen the family to include such taxa as quail-thrushes, whipbirds, cuckoo-shrikes, and birds of paradise within a much bigger Corvidae family, placing the corvids together in a Corvinae subfamily. They argue that the enlarged family originated in Australia;

since only members of the Corvus genus now live in Australia, they would have been recent re-colonists of their ancestral home.

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