Historically, the auks were believed to be one of the earliest distinct charadriiform lineages due to their characteristic
morphology, but genetic analyses have demonstrated that these peculiarities are the product of strong natural selection, instead; as opposed to, for example,
plovers (a much older charadriiform lineage), auks radically changed from a wading
shorebird to a diving seabird lifestyle. Thus today, the auks are no longer separated in their own suborder (Alcae), but are considered part of the
Lari suborder, which otherwise contains gulls and similar birds. Judging from genetic data, their closest living relatives appear to be the
skuas, with these two lineages separating about 30
million years ago (Mya). s are auks found in the
Atlantic Ocean. The family contains 25 extant or recently extinct species that are classified into 11 genera. The extant auks (subfamily Alcinae) are broken up into two 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 sequences, 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. Of the genera, only a few species are placed in each. This is probably a product of the rather small geographic range of the family (the most limited of any seabird family), and the periods of
glacial advance and retreat that have kept the populations on the move in a narrow band of subarctic ocean. (
Fratercula cirrhata) Today, as in the past, the auks are restricted to cooler northern waters. Their ability to spread further south is restricted as their prey hunting method, pursuit diving, becomes less efficient in warmer waters. The speed at which small fish (which along with krill are the auk's principal prey) can swim doubles as the temperature increases from , with no corresponding increase in speed for the bird. The southernmost auks, in California and Mexico, can survive there because of cold
upwellings. The current paucity of auks in the Atlantic (six species), compared to the Pacific (19–20 species) is considered to be because of extinctions to the Atlantic auks; the fossil record shows many more species were in the Atlantic during the Pliocene. Auks also tend to be restricted to continental-shelf waters and breed on few oceanic islands.
Hydotherikornis oregonus (Described by Miller in 1931), the oldest purported alcid from the Eocene of California, is actually a petrel (as reviewed by Chandler in 1990) and is reassigned to the tubenoses (Procellariiformes). A 2003 paper, "The Earliest North American Record of Auk (Aves: Alcidae) From the Late Eocene of Central Georgia", reports a Late Eocene, wing-propelled, diving auk from the Priabonain stage of the Late Eocene. These sediments have been dated through Chandronian NALMA {North American Land Mammal Age}, at an estimate of 34.5 to 35.5 million years on the Eocene time scale for fossil-bearing sediments of the Clinchfield Formation, Gordon, Wilkinson County, Georgia. Furthermore, the sediments containing this unabraded portion of a left humerus (43.7 mm long) are tropical or subtropical as evidenced by a wealth of warm-water shark teeth, palaeophied snake vertebrae, and turtles. ==Systematics==