Limnofregata

Taxobox
name = "Limnofregata"
status = fossil
fossil_range = Early Eocene
regnum = Animalia
phylum = Chordata
classis = Aves
ordo = Pelecaniformes
familia = Fregatidae
genus = "Limnofregata"
genus_authority = Olson, 1977
subdivision_ranks = Species
subdivision = "Limnofregata azygosternon" (type) "Limnofregata hasegawai"

"Limnofregata" ("Freshwater frigatebird") is an extinct genus of primitive frigatebird. The two known species were described after fossils from the Early Eocene Green River Formation (c.49 MYA) 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.

Physically "Limnofregata" looked similar to modern frigatebirds, but had shorter legs and wings. They stood 30-40 cm tall when on the ground and had a wingspan of about 100-120 cm. 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.

"Limnofregata" is thought to have lived like a skua. 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.

References

* Olson, Storrs L. (1977): A Lower Eocene frigatebird from the Green River Formation of Wyoming (Pelecaniformes, Fregatidae). "Smithsonian Contributions to Paleobiology" 35: 1–33. [http://www.sil.si.edu/smithsoniancontributions/Paleobiology/pdf_hi/SCtP-0035.pdf PDF fulltext (File szie 12.5MB)]
* Olson, Storrs L. & Matsuoka, Hiroshige (2005): New specimens of the early Eocene frigatebird "Limnofregata" (Pelecaniformes: Fregatidae), with the description of a new species. "Zootaxa" 1046: 1–15. [http://www.nmnh.si.edu/vert/birds/pdf/slo5.pdf PDF fulltext]