Sabine's gull treated as comprising a monotypic genus; it is only placed within the genus "Larus" when the genus is enlarged. The black bill and notched tail are almost unique within the gulls, as they are shared only with the swallow-tailed gull of the Galapagos. On the basis of this the two species were often thought to be each other's closest relatives, a hypothesis ruled out by a number of behaviour and ecological differences. Mitochondrial DNA studies confirmed that they are not closely related, and the closest relative of the Sabine's gull is now thought to be the ivory gull, another Arctic
Ring-tailed lemur Molecular analysis suggests that either the bamboo lemurs diverged from the ring-tailed lemur, making the group monophyletic and supporting the current 3-genera taxonomy, or that the ring-tailed lemur is nested in with the bamboo lemurs. The karyotype of the ring-tailed lemur has 56 chromosomes, of which four are metacentric (arms of nearly equal length), four are submetacentric (arms of unequal length), and 46 are acrocentric (the short arm is hardly observable). The X chromosome is metacentric and the Y chromosome is acrocentric. Linnaeus first used the genus name "Lemur" to describe ""Lemur tardigradus"" (the red slender loris, now known as