The extant auks (subfamily Alcinae) are broken up into 2 main groups: the usually high-billed puffins (tribe Fraterculini) and auklets (tribe Aethiini), as opposed to the more slender-billed murres and true auks (tribe Alcini), and the murrelets and guillemots (tribes Brachyramphini and Cepphini). The tribal arrangement was originally based on analyses of morphology and ecology. mtDNA cytochrome "b" sequence and allozyme studies confirm these findings except that the "Synthliboramphus" murrelets should be split into a distinct tribe, as they appear more closely related to the Alcini – in any case, assumption of a closer relationship between the former and the true guillemots was only weakly supported by earlier studies.