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Larus

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The genus *Larus* represents a large group of gulls found across the entire globe.

Ring species seagull
Ring species seagull

While they live everywhere, the highest diversity of species is found in the Northern Hemisphere. Many of these birds are common and well-known in their specific ranges. Most people colloquially refer to these birds as "seagulls." Historically, scientists placed almost all gulls into this single genus. However, research between 2005 and 2007 changed this classification. Scientists discovered that the old arrangement was polyphyletic. This means the group did not share a single common ancestor. Because of this, several other genera were resurrected. These include *Chroicocephalus*, *Ichthyaetus*, *Hydrocoloeus*, and *Leucophaeus*.

Physically, members of *Larus* are generally medium to large birds. Most species display a pattern of pale grey or black on their upper parts. Their undersides and heads are typically white. Many gulls also feature black markings on their wingtips. These markings often include small white spots known as "mirrors." Some species also possess black markings on their tails. These birds possess stout, longish bills and webbed feet. Their appearance can change depending on the season. In winter, the head feathers are often streaked or smudged with dark grey. Young birds look quite different from adults. They are brown and require three to five years to reach adult plumage. They pass through subadult plumages that look intermediate between the young and adult stages.

The history of this genus begins with the Swedish naturalist Carl Linnaeus. He introduced the genus *Larus* in 1758. He published this in the tenth edition of his work, *Systema Naturae*. The name is derived from the Ancient Greek *laros* or the Latin *larus*. These terms likely referred to a gull or another large seabird. The type species for the genus is the great black-backed gull, *Larus marinus*. This specific name translates to "sea gull."

Scientists continue to study the taxonomy of these birds. For example, the taxonomy of the herring and lesser black-backed gull complex is very complicated. Depending on the authority, this group may be recognized as two species or as many as eight species.

We can learn about the history of *Larus* through the fossil record. Fossils of these gulls are known from the Middle Miocene epoch. This period occurred about 20 to 15 million years ago. Scientists generally reject the idea that earlier fossils belong to this genus. Biogeography suggests that the genus evolved in the northern Atlantic. During the Pliocene, the gulls spread globally. This was a time when species diversity appeared to be at its highest.

Fossil evidence has been found in several locations. These include Grund, Austria, and Romania. Other fossils have been discovered in the southeastern United States. Examples include *Larus elmorei* from the Middle Pliocene of Bone Valley. Other species like *Larus lacus* and *Larus perpetuus* also come from the Pliocene of the southeastern U.S.

One of the most famous biological concepts involves these gulls. The circumpolar group of *Larus* species is often cited as a classic example of a ring species.

Ring species seagull
Ring species seagull

In this model, the ranges of the gulls form a ring around the North Pole. The birds form a chain of interbreeding populations. For instance, the European herring gull can hybridize with the American herring gull. The American herring gull can then breed with the Vega gull. The Vega gull can interbreed with Heuglin's gull. Heuglin's gull can then breed with the Siberian lesser black-backed gull. This last bird is the eastern representative of the lesser black-backed gulls. This chain eventually leads back to northwestern Europe.

Despite this chain, the ring does not close perfectly. The lesser black-backed gulls and the herring gulls are sufficiently different. Because of these differences, they rarely interbreed where their ranges meet in Europe. This creates a continuum of species that eventually separates. This pattern was long used to explain how new species form. However, recent genetic studies have added complexity to this idea. These studies suggest that the ring species model may not be as simple as once thought. Scientists are still working to understand the true genetic relationships within this group.

Understanding *Larus* helps scientists study evolution and biogeography. The way these birds spread from the northern Atlantic tells us about ancient ocean patterns. The way they change plumage over several years shows how they adapt to life cycles. Even the complicated taxonomy of the herring gull complex shows how much we are still learning. As genetic tools improve, our map of the gull family tree continues to change. This makes the genus *Larus* a vital subject for studying how life moves and changes across the planet.

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File:Ring species seagull.svg
Ring species seagull.svg
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