Taxonomy
The Ivory Gull was initially described by Constantine Phipps, 2nd Baron Mulgrave in 1774 as Larus eburneus from a specimen collected on Spitsbergen. Johann Jakob Kaup later recognized the unique traits of the Ivory Gull and gave it a monotypic genus, Pagophila, in 1829. Johan Ernst Gunnerus later gave the species a new specific name, Pagophila alba. Today some authors consider the Ivory Gull not deserving of its monotypic genus, instead to choosing to merge it, along with the other monotypic gulls, back into Larus. However, most authors have not chosen to do so. The Ivory Gull has no subspecies. No fossil members of this genus are known.
This gull is traditionally believed to be most closely related to either the kittiwakes, Sabine's Gull, or Ross's Gull. It differs anatomically from the other genera by having a relatively short tarsometatarsus, a narrower os pubis, and potentially more flexibility in skull kinetic structure. Structurally, it is most similar to the kittiwakes; however, recent genetic analysis based on mtDNA sequences shows that Sabine's Gull is the Ivory Gull's closest relative, followed by the kittiwakes, with Ross's Gull and Swallow-tailed Gull sharing a clade with these species. "Pagophila" is maintained as a unique genus because of the bird’s morphological, behavioral and ecological differences from these species.
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