Larus
Larus is a large genus of gulls with worldwide distribution (by far the greatest species diversity is in the Northern Hemisphere). Many of its species are abundant and well-known birds in their ranges. Until about 2005–2007, most gulls were placed in this genus, but this arrangement is now known to be polyphyletic, leading to the resurrection of the genera "Ichthyaetus", "Chroicocephalus", "Leucophaeus", and "Hydrocoloeus" (this last had been recognized more often than the other genera) for several species traditionally included in "Larus". They are in general medium to large birds, typically grey or white, often with black markings  on their heads or wings. They have stout, longish bills and webbed feet. The taxonomy of the large gulls in the herring and lesser black-backed complex is very complicated, with different authorities recognising between two and eight species. Taxonomy. The genus "Larus" was introduced in 1758 by the Swedish naturalist Carl Linnaeus in the tenth edition of his "Systema Naturae". The genus name is from Ancient Greek "laros" (λάῥος) or Latin "larus", which appears to have referred to a gull or other large seabird. The type species is the great black-backed gull ("Larus marinus"). Species. The genus contains  24 species. Fossils. Fossils of "Larus" gulls are known from the Middle Miocene, about 20-15 million years ago; allocation of earlier fossils to this genus is generally rejected. Biogeography of the fossil record suggests that the genus evolved in the northern Atlantic and spread globally during the Pliocene, when species diversity seems to have been highest, as with most seabirds. ""Larus" raemdonckii" (Early Oligocene of Belgium) is now at least tentatively believed to belong in the procellariiform genus "Puffinus". ""L." elegans" (Late Oligocene?/Early Miocene of St-Gérand-le-Puy, France) and ""L." totanoides" (Late Oligocene?/Early Miocene of southeastern France ) are now in "Laricola", while ""L." dolnicensis" (Early Miocene of the Czech Republic) was actually a pratincole; it is now placed in "Mioglareola". The Early Miocene ""Larus" desnoyersii" (southeastern France) and ""L." pristinus" (John Day Formation, Willow Creek, U.S.) probably do not belong in this genus; the former may be a skua. Ring species. The circumpolar group of "Larus" gull species has often been cited as a classic example of the ring species. The range of these gulls forms a ring around the North Pole. The European herring gull, which lives primarily in Great Britain and Northern Europe, can hybridize  with the American herring gull (living in North America), which can also interbreed with the Vega or East Siberian gull, the western subspecies of which, Birula's gull, can hybridize with Heuglin's gull which, in turn, can interbreed with the Siberian lesser black-backed gull (all four of these live across the north of Siberia). The last is the eastern representative of the lesser black-backed gulls back in northwestern Europe, including Great Britain. However, the lesser black-backed gulls and herring gull are sufficiently different that they rarely interbreed; thus, the group of gulls forms a continuum except  in Europe, where the two lineages meet. However, a recent genetic study has shown that this example is far more complicated than presented here, and probably does not constitute a true ring species.