Alcinae - Evolution and Distribution

Evolution and Distribution

See also: List of Charadriiformes by population

Traditionally, the auks were believed to be one of the earliest distinct charadriiform lineages due to their characteristic morphology. However, 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). Alternatively, auks may have split off far earlier from the rest of the Lari and undergone strong morphological, but slow genetic evolution, which would require a very high evolutionary pressure, coupled with a long lifespan and slow reproduction.

The earliest unequivocal fossils of auks are from the late Eocene, some 35 mya. The genus Miocepphus, (from the Miocene, 15 mya) is the earliest known from good specimens. Two very fragmentary fossils are often assigned to the Alcidae, although this may not be correct: Hydrotherikornis (late Eocene) and Petralca (Late Oligocene). Most extant genera are known to exist since the Late Miocene or Early Pliocene (c. 5 mya). Miocene fossils have been found in both California and Maryland, but the greater diversity of fossils and tribes in the Pacific leads most scientists to conclude that it was there they first evolved, and it is in the Miocene Pacific that the first fossils of extant genera are found. Early movement between the Pacific and the Atlantic probably happened to the south (since there was no northern opening to the Atlantic), later movements across the Arctic Ocean. The flightless subfamily Mancallinae, which was apparently restricted to the Pacific coast of southern North America and became extinct in the Early Pleistocene, is sometimes includes in the family Alcidae under some definitions.

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.

Compared to other families of seabirds, there are no genera with many species (such as the 47 Larus gulls). 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.

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 food items) can swim doubles as the temperature increases from 5°C to 15°C, 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 (6 species), compared to the Pacific (19-20 species) is considered to be because of extinctions to the Atlantic auks; the fossil record shows there were many more species 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 entitled "The Earliest North American Record of Auk (Aves: Alcidae) From the Late Eocene of Central Georgia" by Robert M. Chandler and Dennis Parmley of Georgia College and State University 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 unabraided portion of a left humerus (43.7mm long) are tropical or sub-tropical as evidenced by a wealth of warm water shark teeth, palaeophied snake vertebrae and turtles.

Read more about this topic:  Alcinae

Other articles related to "evolution, evolution and distribution":

Intelligent Design Movement - Philosophy
... James Kennedy of Coral Ridge Ministries, Johnson gave a speech called How the Evolution Debate Can Be Won ... its strategy for winning the battle "To talk of a purposeful or guided evolution is not to talk about evolution at all ... When you understand it that way, you realize that the Darwinian theory of evolution contradicts not just the Book of Genesis, but every word in the Bible from beginning to end ...
Tropicbird - Systematics, Evolution and Distribution
... Recent research suggests that the Pelecaniformes as traditionally defined are paraphyletic too ... The tropicbirds and the related prehistoric family Prophaethontidae are considered a distinct order, Phaethontiformes, not closely related to any other living birds ...
John Maynard Smith Prize - List of Winners
1997 Marie-Charlotte Anstett Facilitation and constraints in the evolution of mutualism 1999 Nicolas Galtier Non stationary models of nucleotide substitution and the evolution of base composition 2001 ...
Evolution - Social and Cultural Responses
... Further information Social effect of evolutionary theory and Objections to evolution In the 19th century, particularly after the publication of On the Origin of Species in 1859, the idea that life had ... However, evolution remains a contentious concept for some theists ... religions and denominations have reconciled their beliefs with evolution through concepts such as theistic evolution, there are creationists who believe that ...

Famous quotes containing the words distribution and/or evolution:

    There is the illusion of time, which is very deep; who has disposed of it? Mor come to the conviction that what seems the succession of thought is only the distribution of wholes into causal series.
    Ralph Waldo Emerson (1803–1882)

    Analyze theory-building how we will, we all must start in the middle. Our conceptual firsts are middle-sized, middle-distanced objects, and our introduction to them and to everything comes midway in the cultural evolution of the race.
    Willard Van Orman Quine (b. 1908)