Limnofregata
Encyclopedia
Limnofregata is an extinct genus
of primitive frigatebird
. The two known species were described after fossils from the Early Eocene
Green River Formation
(c.49 million years ago) of Wyoming
. A number of good complete and partial skeletons, some with feather impressions, are known of the type species, and L. hasegawai is known from two skulls and most of one torso.
s. They stood 30 to 40 cm (11.8 to 15.7 in) tall when on the ground and had a wingspan of about 100 to 120 cm (3.3 to 3.9 ft). The beak
was shorter than that of modern frigatebirds, and lacked the typical hook at the end, resembling a strong booby
beak more than that of today's frigatebirds. The species differ conspicuously in size, with L. hasegawai being as much larger when compared to L. azygosternon as today's largest species of frigatebird (Fregata minor) is compared to the smallest extant one (Fregata ariel). The bill of hasegawai was notably larger still than that of its congener
, whereas its feet were smaller, echoing a pattern found in the extant Fregata species.
. It inhabited the freshwater or brackish lakes that had in its time formed in today's Green River
valley due to the uplift of the Rocky Mountains
, where it fed on smaller vertebrates and probably harassed other shorebirds for food and feasted on dead fish (e.g. Knightia
) during summer dieoffs due to oxygen depletion in the eutrophic lakes. Modern frigatebirds show pronounced sexual dimorphism
in size, apparently to avoid competition due to different soaring
behavior of male and female wings. As Limnofregata was most likely not a soaring bird, it can be expected that the sexes were much alike. It is not known if the males had a prominent throat balloon for advertising for mates as in the modern relatives, but Limnofregata throat bones at least did differ markedly from those of modern frigatebirds.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of primitive frigatebird
Frigatebird
The frigatebirds are a family, Fregatidae, of seabirds. There are five species in the single genus Fregata. They are also sometimes called Man of War birds or Pirate birds. Since they are related to the pelicans, the term "frigate pelican" is also a name applied to them...
. The two known species were described after fossils from the Early 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...
Green River Formation
Green River Formation
The Green River Formation is an Eocene geologic formation that records the sedimentation in a group of intermountain lakes. The sediments are deposited in very fine layers, a dark layer during the growing season and a light-hue inorganic layer in winter. Each pair of layers is called a varve and...
(c.49 million years ago) of Wyoming
Wyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...
. A number of good complete and partial skeletons, some with feather impressions, are known of the type species, and L. hasegawai is known from two skulls and most of one torso.
Size
Physically Limnofregata looked similar to modern frigatebirds, but had shorter legs and wingWing
A wing is an appendage with a surface that produces lift for flight or propulsion through the atmosphere, or through another gaseous or liquid fluid...
s. They stood 30 to 40 cm (11.8 to 15.7 in) tall when on the ground and had a wingspan of about 100 to 120 cm (3.3 to 3.9 ft). The beak
Beak
The beak, bill or rostrum is an external anatomical structure of birds which is used for eating and for grooming, manipulating objects, killing prey, fighting, probing for food, courtship and feeding young...
was shorter than that of modern frigatebirds, and lacked the typical hook at the end, resembling a strong booby
Booby
A booby is a seabird in the genus Sula, part of the Sulidae family. Boobies are closely related to the gannets , which were formerly included in Sula.-Description:...
beak more than that of today's frigatebirds. The species differ conspicuously in size, with L. hasegawai being as much larger when compared to L. azygosternon as today's largest species of frigatebird (Fregata minor) is compared to the smallest extant one (Fregata ariel). The bill of hasegawai was notably larger still than that of its congener
Congener
Congener has several different meanings depending on the field in which it is used. Colloquially, it is used to mean a person or thing like another, in character or action.-Biology:In biology, congeners are organisms within the same genus...
, whereas its feet were smaller, echoing a pattern found in the extant Fregata species.
Lifestyle
Limnofregata is thought to have lived like a skuaSkua
The skuas are a group of seabirds with about seven species forming the family Stercorariidae and the genus Stercorarius. The three smaller skuas are called jaegers in North America....
. It inhabited the freshwater or brackish lakes that had in its time formed in today's Green River
Green River (Utah)
The Green River, located in the western United States, is the chief tributary of the Colorado River. The watershed of the river, known as the Green River Basin, covers parts of Wyoming, Utah, and Colorado. The Green River is long, beginning in the Wind River Mountains of Wyoming and flowing...
valley due to the uplift of the Rocky Mountains
Rocky Mountains
The Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in western Canada, to New Mexico, in the southwestern United States...
, where it fed on smaller vertebrates and probably harassed other shorebirds for food and feasted on dead fish (e.g. Knightia
Knightia
Knightia is an extinct genus of bony fish which lived in the fresh water lakes and rivers of North America during the Eocene epoch. It was named by David Starr Jordan in 1907, in honor of the late University of Wyoming professor Wilbur Clinton Knight, "an indefatigable student of the paleontology...
) during summer dieoffs due to oxygen depletion in the eutrophic lakes. Modern frigatebirds show pronounced sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
in size, apparently to avoid competition due to different soaring
Lift (soaring)
Gliding flight is heavier-than-air flight without the use of thrust. It is employed by gliding animals and by aircraft such as gliders. The most common human application of gliding flight is in sport and recreation using aircraft designed for this purpose...
behavior of male and female wings. As Limnofregata was most likely not a soaring bird, it can be expected that the sexes were much alike. It is not known if the males had a prominent throat balloon for advertising for mates as in the modern relatives, but Limnofregata throat bones at least did differ markedly from those of modern frigatebirds.