Gaviiformes
Encyclopedia
Gaviiformes is an order
of aquatic birds containing the loon
s or divers and their closest extinct relatives. Modern gaviiformes are found in many parts of North America
and northern Eurasia
(Europe, Asia and debatably Africa), though prehistoric species were more widespread.
There are five living species, and all are placed in the genus Gavia. The loons were formerly often considered to be the most ancient of the northern hemisphere bird families; this idea grew basically out of the perceived similarity of shape and (probably) habits between loons and the entirely unrelated extinct Cretaceous
order Hesperornithiformes
. In particular Enaliornis
, which was apparently an ancestral and plesiomorphic member of that order, was sometimes used to support claims of Albian
(Early Cretaceous
) Gaviiformes.
More recently, it has become clear that the Anseriformes
(waterfowl) and the Galliformes
are the most ancient groups of modern birds, and these being distinct by the end of the Albian 100 million years ago (Ma), while just possible, is not at all well-supported. Loons belong to a more modern radiation. They were once believed to be related to grebes, which are also foot-propelled diving birds, and both species were once classified together under the order Colymbiformes
. However, as recently as the 1930s, it was determined that the two groups are not that closely related at all and are merely the product of convergent evolution
and adapted in a similar way to a similar ecological niche
. The similarity is so strong that even the most modern cladistic analyses of general anatomical features are easily misled into grouping loons and grebes.
The Sibley-Ahlquist taxonomy
still allied the loons with the grebes in its massively paraphyletic "Ciconiiformes", and it is almost certain that the relationships of loons lie with some of the orders placed therein. Namely, other recent authors have considered loons to share a rather close relationship with seabird
s such as penguin
s (Sphenisciformes), tubenoses (Procellariiformes
), wader
s (Charadriiformes) – and perhaps the newly-discovered clade
Mirandornithes
which unites grebes (Podicipediformes) and their closest living relatives, the flamingos (Phoenicopteriformes). It is perhaps notable that some early penguins had skulls and beaks that were in many aspects similar to those of the known living and fossil Gaviiformes.
In prehistoric times, the loons had a more southerly distribution than today, and their fossils have been found in places such as California
, Florida
and Italy
. The conflicting molecular data regarding their relationships is not much resolved by the fossil
record; though they seem to have originated at the end of the Late Cretaceous
like their presumed relatives, modern loons are only known with certainty since the Eocene
. By that time almost all modern bird orders are at least strongly suspected to have existed – if not known from unequivocally identified specimens – anyway.
Colymboides
, the oldest unequivocal gaviiform genus known as of 2009, is widely known from early Priabonian
– about 37 million years ago (Ma) in the Late Eocene – to Early Miocene
(late Burdigalian
, less than 20 Ma) limnic and marine
rocks of western Eurasia
north of the Alpide belt
, between the Atlantic and the former Turgai Sea
. It is usually placed in the Gaviidae already, but usually in a subfamily Colymboidinae, with the modern-type loons making up the Gaviinae. But the Colymboides material is generally quite distinct from modern loons, and may actually belong in a now-extinct family of primitive gaviiforms. Furthermore, the supposed genus could well be paraphyletic, so that for example Dyspetornis – which is now contained therein – might have to be separated again. A leg of an undescribed small diver was found in the Late Oligocene deposits at Enspel
(Germany
); it too may or may not belong to Colymboides. Of the crown genus
Gavia, nearly ten prehistoric species have been named to date, and about as many undescribed ones await further study. The genus is known from the Early Miocene onwards, and the oldest members them are rather small (some are smaller than the Red-throated Diver
). Throughout the late Neogene
, the genus by and large follows Cope's Rule
.
Some older fossils are sometimes assigned to the Gaviiformes. From the Late Cretaceous
, the genera Lonchodytes
(Lance Formation
, Wyoming) and Neogaeornis
(Quinriquina Formation, Chile
) have been described; both are usually allied with orders which are considered related to loons. In particular the latter is still sometimes explicitly proposed as a primitive loon as they both were initially, but other authors consider Neogaeornis a hesperornithiform
; note however that neither Gaviiformes nor Hesperornithiformes are known from the Southern Hemisphere
or anywhere near it. Lonchodytes was more certainly quite close to loons, but probably closer still to some of the loons' relatives. Of similarly doubtful validity and surrounded by considerable dispute is the Late Cretaceous loon Polarornis
(Seymour Island
, Antarctica). Eupterornis from the Paleocene
of Châlons-sur-Vesle
(France
) has some features reminiscent of loons, but others seem more similar to Charadriiformes
such as gulls (Laridae). A piece of a carpometacarpus
supposedly from Oligocene
rocks near Lusk, Wyoming
was described as Gaviella pusilla, but this handbone also shows some similarities to the plotopterids which were flightless wing-propelled divers and if these are apomorphic would make an unconvincing member of the Gaviidae (though it still could be a small-winged gaviiform in an – as of yet undescribed – family "Gaviellidae"): while the carpometacarpus in Gavia is somewhat convergent
to that of wing-propelled divers, enabling the wings to be used as rudders for quick underwater turns, Colymboides still had an unspecialized plesiomorphic hand. Parascaniornis, sometimes allied to the loons by early authors, was eventually determined to be a junior synonym of the hesperornithiform Baptornis
. A supposed mid-Eocene
diver fossil form Geiseltal
(Germany
) was erroneously assigned to Gavia.
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
of aquatic birds containing the loon
Loon
The loons or divers are a group of aquatic birds found in many parts of North America and northern Eurasia...
s or divers and their closest extinct relatives. Modern gaviiformes are found in many parts of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
and northern Eurasia
Eurasia
Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...
(Europe, Asia and debatably Africa), though prehistoric species were more widespread.
Classification and evolution
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
order Hesperornithiformes
Hesperornithiformes
Hesperornithes is an extinct and highly specialized clade of Cretaceous toothed birds. Hesperornithine birds, apparently limited to former aquatic habitats in the Northern Hemisphere, include genera such as Hesperornis, Parahesperornis, Baptornis, Enaliornis, and probably Potamornis, all...
. In particular Enaliornis
Enaliornis
Enaliornis is a genus of hesperornithine bird which lived in the late Early Cretaceous, making it the oldest known hesperornithine. Fossils have been found near Cambridge, England...
, which was apparently an ancestral and plesiomorphic member of that order, was sometimes used to support claims of Albian
Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous epoch/series. Its approximate time range is 112.0 ± 1.0 Ma to 99.6 ± 0.9 Ma...
(Early Cretaceous
Early Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
) Gaviiformes.
More recently, it has become clear that the Anseriformes
Anseriformes
The order Anseriformes contains about 150 living species of birds in three extant families: the Anhimidae , Anseranatidae , and the Anatidae, which includes over 140 species of waterfowl, among them the ducks, geese, and swans.All species in the order are highly adapted for an aquatic existence at...
(waterfowl) and the Galliformes
Galliformes
Galliformes are an order of heavy-bodied ground-feeding domestic or game bird, containing turkey, grouse, chicken, New and Old World Quail, ptarmigan, partridge, pheasant, and the Cracidae. Common names are gamefowl or gamebirds, landfowl, gallinaceous birds or galliforms...
are the most ancient groups of modern birds, and these being distinct by the end of the Albian 100 million years ago (Ma), while just possible, is not at all well-supported. Loons belong to a more modern radiation. They were once believed to be related to grebes, which are also foot-propelled diving birds, and both species were once classified together under the order Colymbiformes
Colymbiformes
Colymbiformes is a disused order of birds that was once used to classify grebes and loons. Scientific study has revealed that these two types of waterbirds are not so closely related; they have been reclassified in the orders Podicipediformes and Gaviiformes, respectively.-References:*....
. However, as recently as the 1930s, it was determined that the two groups are not that closely related at all and are merely the product of convergent evolution
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
and adapted in a similar way to a similar ecological niche
Ecological niche
In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...
. The similarity is so strong that even the most modern cladistic analyses of general anatomical features are easily misled into grouping loons and grebes.
The Sibley-Ahlquist taxonomy
Sibley-Ahlquist taxonomy
The Sibley-Ahlquist taxonomy is a bird taxonomy proposed by Charles Sibley and Jon Edward Ahlquist. It is based on DNA-DNA hybridization studies conducted in the late 1970s and throughout the 1980s....
still allied the loons with the grebes in its massively paraphyletic "Ciconiiformes", and it is almost certain that the relationships of loons lie with some of the orders placed therein. Namely, other recent authors have considered loons to share a rather close relationship with seabird
Seabird
Seabirds are birds that have adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations...
s such as penguin
Penguin
Penguins are a group of aquatic, flightless birds living almost exclusively in the southern hemisphere, especially in Antarctica. Highly adapted for life in the water, penguins have countershaded dark and white plumage, and their wings have become flippers...
s (Sphenisciformes), tubenoses (Procellariiformes
Procellariiformes
Procellariiformes is an order of seabirds that comprises four families: the albatrosses, petrels and shearwaters, storm petrels, and diving petrels...
), wader
Wader
Waders, called shorebirds in North America , are members of the order Charadriiformes, excluding the more marine web-footed seabird groups. The latter are the skuas , gulls , terns , skimmers , and auks...
s (Charadriiformes) – and perhaps the newly-discovered clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
Mirandornithes
Mirandornithes
Mirandornithes is a clade that consists of flamingos and grebes. The relationships of both groups have been problematic. Flamingos had been placed with numerous branches within Neognathae, such as ducks and storks. The grebes had been placed with the loons. However recent studies seem to confirm...
which unites grebes (Podicipediformes) and their closest living relatives, the flamingos (Phoenicopteriformes). It is perhaps notable that some early penguins had skulls and beaks that were in many aspects similar to those of the known living and fossil Gaviiformes.
Fossil record
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
and Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
. The conflicting molecular data regarding their relationships is not much resolved by the fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
record; though they seem to have originated at the end of the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
like their presumed relatives, modern loons are only known with certainty since the Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
. By that time almost all modern bird orders are at least strongly suspected to have existed – if not known from unequivocally identified specimens – anyway.
Colymboides
Colymboides
The genus Colymboides contains two species of early loon dating from the late Oligocene or early Miocene. They are considered to be the earliest known unambiguous gaviiform fossils...
, the oldest unequivocal gaviiform genus known as of 2009, is widely known from early Priabonian
Priabonian
The Priabonian is, in the ICS's geologic timescale, the latest age or the upper stage of the Eocene epoch or series. It spans the time between and...
– about 37 million years ago (Ma) in the Late Eocene – to Early Miocene
Early Miocene
The Early Miocene is a sub-epoch of the Miocene Epoch made up of two stages: the Aquitanian and Burdigalian stages....
(late Burdigalian
Burdigalian
The Burdigalian is, in the geologic timescale, an age or stage in the early Miocene. It spans the time between 20.43 ± 0.05 Ma and 15.97 ± 0.05 Ma...
, less than 20 Ma) limnic and marine
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
rocks of western Eurasia
Eurasia
Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...
north of the Alpide belt
Alpide belt
The Alpide belt is a mountain range which extends along the southern margin of Eurasia. Stretching from Java to Sumatra through the Himalayas, the Mediterranean, and out into the Atlantic, it includes the Alps, the Carpathians, the mountains of Asia Minor and Iran, the Hindu Kush, the Himalayas,...
, between the Atlantic and the former Turgai Sea
Turgai Sea
The Turgai Sea or Turgai Strait, also known as the West Siberian Sea, was a large shallow body of salt water of the Mesozoic and Cenozoic Eras...
. It is usually placed in the Gaviidae already, but usually in a subfamily Colymboidinae, with the modern-type loons making up the Gaviinae. But the Colymboides material is generally quite distinct from modern loons, and may actually belong in a now-extinct family of primitive gaviiforms. Furthermore, the supposed genus could well be paraphyletic, so that for example Dyspetornis – which is now contained therein – might have to be separated again. A leg of an undescribed small diver was found in the Late Oligocene deposits at Enspel
Enspel
Enspel is an Ortsgemeinde – a community belonging to a Verbandsgemeinde – in the Westerwaldkreis in Rhineland-Palatinate, Germany.-Location:...
(Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
); it too may or may not belong to Colymboides. Of the crown genus
Crown group
A crown group is a group consisting of living representatives, their ancestors back to the most recent common ancestor of that group, and all of that ancestor's descendants. The name was given by Willi Hennig, the formulator of phylogenetic systematics, as a way of classifying living organisms...
Gavia, nearly ten prehistoric species have been named to date, and about as many undescribed ones await further study. The genus is known from the Early Miocene onwards, and the oldest members them are rather small (some are smaller than the Red-throated Diver
Red-throated Diver
The Red-throated Loon or Red-throated Diver is a migratory aquatic bird found in the northern hemisphere. It breeds primarily in Arctic regions, and winters in northern coastal waters. It is the most widely distributed member of the loon or diver family. Ranging from in length, the Red-throated...
). Throughout the late Neogene
Neogene
The Neogene is a geologic period and system in the International Commission on Stratigraphy Geologic Timescale starting 23.03 ± 0.05 million years ago and ending 2.588 million years ago...
, the genus by and large follows Cope's Rule
Cope's rule
Cope's rule states that population lineages tend to increase in body size over evolutionary time. While the rule has been demonstrated in many instances, it does not hold true at all taxonomic levels, or in all clades...
.
Some older fossils are sometimes assigned to the Gaviiformes. From the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
, the genera Lonchodytes
Lonchodytes
Lonchodytes is a Late Cretaceous genus of aquatic bird, which lived along the shores of the Western Interior Seaway. It lived probably during the Maastrichtian, 70 million years ago , and was found in Lance Creek Formation rocks in Wyoming though it seems still somewhat unclear if it did fossilize...
(Lance Formation
Lance Formation
The Lance Formation is a division of Late Cretaceous rocks in the western United States. Named after Lance Creek, Wyoming, the microvertebrate fossils and dinosaurs represent important components of the latest Mesozoic vertebrate faunas...
, Wyoming) and Neogaeornis
Neogaeornis
Neogaeornis is a controversial prehistoric genus of diving bird. The single known species, Neogaeornis wetzeli, was described from fossils found in the Campanian to Maastrichtian Quiriquina Formation of Chile. It lived about 70-67 million years ago...
(Quinriquina Formation, Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
) have been described; both are usually allied with orders which are considered related to loons. In particular the latter is still sometimes explicitly proposed as a primitive loon as they both were initially, but other authors consider Neogaeornis a hesperornithiform
Hesperornithiformes
Hesperornithes is an extinct and highly specialized clade of Cretaceous toothed birds. Hesperornithine birds, apparently limited to former aquatic habitats in the Northern Hemisphere, include genera such as Hesperornis, Parahesperornis, Baptornis, Enaliornis, and probably Potamornis, all...
; note however that neither Gaviiformes nor Hesperornithiformes are known from the Southern Hemisphere
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...
or anywhere near it. Lonchodytes was more certainly quite close to loons, but probably closer still to some of the loons' relatives. Of similarly doubtful validity and surrounded by considerable dispute is the Late Cretaceous loon Polarornis
Polarornis
Polarornis is a genus of prehistoric bird, possibly a loon. It contains a single species Polarornis gregorii known from incomplete remains of one individual found on Seymour Island, Antarctica, in rocks which are dated to the Late Cretaceous .The discovery of Polarornis gregorii was first announced...
(Seymour Island
Seymour Island
Seymour Island is an island in the chain of 16 major islands around the tip of the Graham Land on the Antarctic Peninsula. Graham Land is closer to continental land mass than any other part of that Antarctica. It lies within the section of the island chain that resides off the west side of the...
, Antarctica). Eupterornis from the Paleocene
Paleocene
The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...
of Châlons-sur-Vesle
Châlons-sur-Vesle
Châlons-sur-Vesle is a commune in the Marne department in north-eastern France.-See also:*Communes of the Marne department...
(France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
) has some features reminiscent of loons, but others seem more similar to Charadriiformes
Charadriiformes
Charadriiformes is a diverse order of small to medium-large birds. It includes about 350 species and has members in all parts of the world. Most Charadriiformes live near water and eat invertebrates or other small animals; however, some are pelagic , some occupy deserts and a few are found in thick...
such as gulls (Laridae). A piece of a carpometacarpus
Carpometacarpus
The carpometacarpus is the fusion of the carpal and metacarpal bone, essentially a single fused bone between the wrist and the knuckles. It is a smallish bone in most birds, generally flattened and with a large hole in the middle. In flightless birds, however, its shape may be slightly different,...
supposedly from Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
rocks near Lusk, Wyoming
Lusk, Wyoming
Lusk is a town in Niobrara County, Wyoming, United States. The population was 1,447 at the 2000 census. It is the county seat of Niobrara County. The town was laid out in June 1886 by engineers working on the Wyoming Central Railway. It was named after Frank S...
was described as Gaviella pusilla, but this handbone also shows some similarities to the plotopterids which were flightless wing-propelled divers and if these are apomorphic would make an unconvincing member of the Gaviidae (though it still could be a small-winged gaviiform in an – as of yet undescribed – family "Gaviellidae"): while the carpometacarpus in Gavia is somewhat convergent
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
to that of wing-propelled divers, enabling the wings to be used as rudders for quick underwater turns, Colymboides still had an unspecialized plesiomorphic hand. Parascaniornis, sometimes allied to the loons by early authors, was eventually determined to be a junior synonym of the hesperornithiform Baptornis
Baptornis
Baptornis is an extinct genus of flightless aquatic bird from the Late Cretaceous, some 87-80 million years ago . The fossils of Baptornis advenus, the type species, were discovered in Kansas, which at its time was mostly covered by the Western Interior Seaway, a shallow shelf sea...
. A supposed mid-Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
diver fossil form Geiseltal
Geiseltal
The Geisel valley is a valley in Saxony-Anhalt, Germany, situated west of Merseburg, Saalekreis district. It is named after the River Geisel which rises in Mücheln and is a tributary of the Saale, just under 25 km long....
(Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
) was erroneously assigned to Gavia.