''Thiornis'' is a fossil genus of

Middle Miocene The Middle Miocene is a sub-epoch of the Miocene epoch (geology), epoch made up of two Stage (stratigraphy), stages: the Langhian and Serravallian stages. The Middle Miocene is preceded by the Early Miocene. The sub-epoch lasted from 15.97 ± 0. ...

grebe Grebes () are aquatic diving birds in the order (biology), order Podicipediformes (). Grebes are widely distributed freshwater birds, with some species also found in sea, marine habitats during Bird migration, migration and winter. Most grebes f ...

known from a nearly complete specimen from Libros, Spain. Originally classified as a type of

moorhen Moorhens—sometimes called marsh hens—are medium-sized water birds that are members of the rail family (Rallidae). Most species are placed in the genus ''Gallinula'', Latin for "little hen." They are close relatives of coots. They are ...

, ''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''.

History

The specimen was described by the Spanish Jesuit priest and

entomologist Entomology (from Ancient Greek ἔντομον (''éntomon''), meaning "insect", and -logy from λόγος (''lógos''), meaning "study") is the branch of zoology that focuses on insects. Those who study entomology are known as entomologists. In ...

Longinos Navás Longinos Navás (7 March 1858 Tarragona (province), Cabacés, Tarragona – 31 December 1938 Girona) was a Spain, Spanish entomologist who specialised in Plecoptera and Neuropteroidea. Father Longinos Navás was a Jesuit priest. He publish ...

. Despite being of such distinction, Navás had described several vertebrates from the locality. 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 Paris () is the Capital city, capital and List of communes in France with over 20,000 inhabitants, largest city of France. With an estimated population of 2,048,472 residents in January 2025 in an area of more than , Paris is the List of ci ...

at least since 1930 where it was finally reexamine for a 1995 redescription by American

biologist A biologist is a scientist who conducts research in biology. Biologists are interested in studying life on Earth, whether it is an individual Cell (biology), cell, a multicellular organism, or a Community (ecology), community of Biological inter ...

and

ornithologist Ornithology, from Ancient Greek ὄρνις (''órnis''), meaning "bird", and -logy from λόγος (''lógos''), meaning "study", is a branch of zoology dedicated to the study of birds. Several aspects of ornithology differ from related discip ...

Storrs L. Olson Storrs Lovejoy Olson (April 3, 1944 – January 20, 2021) was an American biologist and ornithologist who spent his career at the Smithsonian Institution, retiring in 2008. One of the world's foremost avian paleontologists, he was best known ...

Description

The holotype of ''Thiornis'' is known from a virtually completed specimen that majority of it consists of postcranial material and even feather impressions (

MNHN The French National Museum of Natural History ( ; abbr. MNHN) is the national natural history museum of France and a of higher education part of Sorbonne University. The main museum, with four galleries, is located in Paris, France, within the ...

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 The horned grebe or Slavonian grebe (''Podiceps auritus'') is a relatively small and Threatened species, threatened species of waterbird in the family Podicipedidae. There are two subspecies, ''P. a. auritus'' (Slavonian grebe), which breed ...

(''Podiceps auritus''). The

coracoid A coracoid is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is present as part of the scapula, but this is n ...

is similar to genera ''

Tachybaptus ''Tachybaptus'' is a genus of small birds of the grebe family. The genus name means "quick diving": it is from Ancient Greek ''takhys'' "quick" and ''bapto'' "I dip". It has representatives over much of the world, including the tropics. These g ...

'' and '' Poliocephalus'', as the head does not project as far ventrally as seen in other extant genera of grebes. The

furcula The (Latin for "little fork"; : furculae) or wishbone is a forked bone found in most birds and some species of non-avian dinosaurs, and is either an interclavicle or formed by the fusion of the two clavicles. In birds, its primary function is ...

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 ''Podiceps'' is a genus of birds in the grebe family. The genus name comes from Latin , "rear-end" and ', "foot", and is a reference to the placement of a grebe's legs towards the rear of its body. It has representatives breeding in all contine ...

''. Wingbones are the same in other grebes being straight, slender and narrower in comparison to other diving birds. The

pelvis The pelvis (: pelves or pelvises) is the lower part of an Anatomy, anatomical Trunk (anatomy), trunk, between the human abdomen, abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also c ...

is compressed laterally, with the posterior portion being broad as the ilia flares outward. The

ischia Ischia ( , , ) is a volcanic island in the Tyrrhenian Sea. It lies at the northern end of the Gulf of Naples, about from the city of Naples. It is the largest of the Phlegrean Islands. Although inhabited since the Bronze Age, as a Ancient G ...

are very long and narrow and extend posteriorly well beyond the

sacrum The sacrum (: sacra or sacrums), in human anatomy, is a triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part of the pelvic cavity, ...

and place oriented towards the point of the ilium. This is another featured that is shared with ''Tachybaptus'' and ''Poliocephalus''. The

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

is identical in all extant genera except ''

Podilymbus ''Podilymbus'' is a genus of birds in the Grebe family, the genus name is derived from Latin ''Podilymbus'', a contraction of ''podicipes'' ("feet at the buttocks", from ''podici-'', "rump-" + ''pes'', "foot")—the origin of the name of the gr ...

'', where the femur of ''Podilymbus'' is more slender and elongated. The

tibiotarsus The tibiotarsus is the large bone between the femur and the tarsometatarsus in the leg of a bird. It is the fusion of the proximal part of the tarsus with the tibia. A similar structure also occurred in the Mesozoic Heterodontosauridae. These ...

is relatively short and wide, a featured shared with ''Podiceps'' though in ''Thiornis'' the femur has an enlarged cnemial crest. The

tarsometatarsus The tarsometatarsus is a bone that is only found in the lower leg of birds and some non-avian dinosaurs. It is formed from the fusion of several bird bones found in other types of animals, and homologous to the mammalian tarsus (ankle bones) a ...

is, however, more similar to the smaller grebe genera like ''Tachybaptus''.

Classification

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. 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''. 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. Alternatively Fjeldså (2004) treated ''Thiornis'' as an ancestral stem-grebe instead.

Paleobiology

The holotype specimen was found in Libros,

Province of Teruel Teruel ( Catalan: ''Terol'' ) is a province of Aragon, in the northeast of Spain. The capital is Teruel. It is bordered by the provinces of Tarragona, Castellón, Valencia (including its exclave Rincón de Ademuz), Cuenca, Guadalajara, and Z ...

from the Libros Basin dating to the

Vallesian The Vallesian age is a period of geologic time (11.6–9.0 Ma) within the Miocene used more specifically with European Land Mammal Ages. It precedes the Turolian age and follows the Astaracian age. The so-called Vallesian Crisis resulted in th ...

. 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 Osteology () is the scientific study of bones, practiced by osteologists . A subdiscipline of anatomy, anthropology, archaeology and paleontology, osteology is the detailed study of the structure of bones, skeletal elements, teeth, microbone morp ...

level.

References

{{Taxonbar, from=Q107341724 Podicipediformes Prehistoric bird genera