Thiornis Temporal range: | |
---|---|
Fossil slab of Thiornis sociata | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Aves |
Order: | Podicipediformes |
Family: | Podicipedidae |
Genus: | † Thiornis Navás, 1922 |
Type species | |
†Thiornis sociata | |
Synonyms | |
Podiceps sociatus(Navás, 1922) sensu Olson, 1995 |
Thiornis is a fossil genus of Middle Miocene grebe known from a nearly complete specimen from Libros, Spain. Originally classified as a type of moorhen, Thiornis has since been classified as a species of grebe. The overall anatomy of the bird is identical to modern grebes. It contains a single species, T. sociata.
The specimen was described by the Spanish Jesuit priest and entomologist Longinos Navás. Despite being of such distinction, Navás had described several vertebrates from the locality. [1] [2] For a while the whereabouts since its description was unknown, but unbeknownst to the scientific community, the slab was on display in the Paris Museum at least since 1930 where it was finally reexamine for a 1995 redescription by American biologist and ornithologist Storrs L. Olson. [2]
The holotype of Thiornis is known from a virtually completed specimen that majority of it consists of postcranial material and even feather impressions (MNHN 1930-1). Parts missing from the bird are the cranial remains, some cervical bones and the toe-bones of the right foot. Based on the dimensional measurement of the bones, Thiornis was closer in size to the horned grebe (Podiceps auritus). The coracoid is similar to genera Tachybaptus and Poliocephalus , as the head does not project as far ventrally as seen in other extant genera of grebes. The furcula is also similar to Tachybaptus and Poliocephalus for the clavicle in lateral view is much less curved, but the shaft is more robust than any of the extant genera. Features in the sternum is identical to modern grebes. The pectoral crest of the humeri is not incised, but rounded and greatly expanded. The shaft of the ulna is also more robust than seen in Podiceps . Wingbones are the same in other grebes being straight, slender and narrower in comparison to other diving birds. The pelvis is compressed laterally, with the posterior portion being broad as the ilia flares outward. The ischia are very long and narrow and extend posteriorly well beyond the sacrum and place oriented towards the point of the ilium. This is another featured that is shared with Tachybaptus and Poliocephalus. The femur is identical in all extant genera except Podilymbus , where the femur of Podilymbus is more slender and elongated. The tibiotarsus is relatively short and wide, a featured shared with Podiceps though in Thiornis the femur has an enlarged cnemial crest. The tarsometatarsus is, however, more similar to the smaller grebe genera like Tachybaptus. [2]
Navás (1922) had initially classified Thiornis as a rallid in the Fulicini tribe with the moorhens, a classification that was supported by subsequent authors until Olson (1995) found the bird to be a grebe instead. While Olson does note the overall similarity between Tachybaptus and Thiornis, postulating there might be some relationship between the two, he recommended classifying the specimen as a species of Podiceps (Podiceps sociatus) due how much larger the specimen is to the extant species of Tachybaptus as well as using Podiceps as placeholder given how morphologically diverse members of Podiceps are. [2] However this view is not supported by other scientists. Storer (2000) argued that the size and dimensions of the bones are not good at determining phylogenetic relationships among grebes alone, thus Thiornis should either be considered a valid genus or at least a species of Tachybaptus. [3] This viewpoint was supported by Ksepka et al. (2013) finding two placements for Thiornis. One being in a massive polytomy with several of the smaller species of grebe and the other being part of a subclade grebes that also includes Tachybaptus and Poliocephalus in a polytomy of their own. [4] Alternatively Fjeldså (2004) treated Thiornis as an ancestral stem-grebe instead. [5]
The holotype specimen was found in Libros, Province of Teruel from the Libros Basin dating to the Vallesian. [1] Despite the age of the fossil, the anatomy of Thiornis suggests an ecology that is not unlike that of those of modern grebes as the group as a whole are homogeneous at the osteological level.
Grebes are aquatic diving birds in the order Podicipediformes. Grebes are widely distributed freshwater birds, with some species also found in marine habitats during migration and winter. Most grebes fly, although some flightless species exist, most notably in stable lakes. The order contains a single family, the Podicipedidae, which includes 22 species in six extant genera.
The horned grebe or Slavonian grebe is a relatively small and threatened species of waterbird in the family Podicipedidae. There are two subspecies: P. a. auritus, which breeds in Eurasia, and P. a. cornutus, which breeds in North America. The Eurasian subspecies is distributed over most of northern Europe and northern Asia, breeding from Greenland east to the Russian Far East. The North American subspecies spans most of Canada and some of the United States. The species got its name from large patches of yellowish feathers located behind the eyes, called "horns", that the birds can raise and lower at will..
The pied-billed grebe is a species of the grebe family of water birds primarily found in ponds throughout the Americas.
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The New Zealand grebe, also known as the New Zealand dabchick or weweia, is a member of the grebe family endemic to New Zealand.
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Miobaptus is a fossil genus of grebe that is known from several specimens collected from Czechia and Lake Baikal dating from the Early Miocene to Middle Miocene. Considered to be one of the most primitive genera of grebes, the anatomy of Miobaptus suggests it was less adapted for the aquatic mode of life than modern grebes, but had better flight maneuverability.
Miodytes is a fossil genus of grebe known from a nearly complete specimen from Valjevo Basin, western Serbia known from an almost complete right wing skeleton. It contains a single species, M. serbicus.
Pliolymbus is a fossil genus of grebe known from the Late Pliocene to Early Pleistocene of United States and Mexico. It is known from a single species, P. baryosteus.
Podilymbus majusculus is an extinct species of grebe recovered from the Piacenzian age of the United States.
Podilymbus wetmorei is an extinct species of grebe recovered from the Late Pleistocene age of the United States.
Podicipedini is a tribe of waterbirds belonging to the family Podicipedidae containing the genera Aechmophorus and Podiceps. Members of this tribe of grebes are characterized based on the presence of nuptial plumes and downy young with a bare crown patch. They are more specialized for diving though the anatomy that enables them to do so makes them weaker to stand upright. Further they have much complex mating dance rituals. Based on these characteristics, other possible genera in the clade include Poliocephalus and Rollandia. Indeed a molecular phylogeny by Ogawa et al. (2015) using genetic data from 3 mitochondrial markers found Podiceps to be paraphyletic in respect to Rollandia, as the latter genus is more closely related to several New World species of the former genus. The inclusion of the Neogene genera of Pliolymbus and Thiornis is based on their possible reclassification as junior synonyms as Podiceps.
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Podiceps solidus is an extinct small species of Upper Miocene to Lower Pliocene grebe from Western Mongolia.
Podilymbini is a potential tribe of waterbirds belonging to the family Podicipedidae containing the genus Podilymbus and Tachybaptus. In comparison to Podicipedini, podilymbins are characterized by the lack of nuptial plumes and the chicks have rufous down in one or more patches on the crown. They are able to stand upright and move around land more so. The mating displays among these birds are simpler.
Podiceps discors is an extinct species of grebe from the Upper Pliocene of western North America. It was similar to the black-necked grebe.