''Sigournea'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

of stem tetrapod from the

Early Carboniferous Early may refer to: History * The beginning or oldest part of a defined historical period, as opposed to middle or late periods, e.g.: ** Early Christianity ** Early modern Europe Places in the United States * Early, Iowa * Early, Texas * Early ...

. The genus contains only one species, the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen( ...

''Sigournea multidentata'', which was named in 2006 by paleontologists John R. Bolt and R. Eric Lombard on the basis of a single lower jaw from Iowa. The jaw came from a fissure-fill deposit of the

St. Louis Limestone The St. Louis Limestone is a large geologic formation covering a wide area of the midwest of the United States. It is named after an exposure at St. Louis, Missouri. It consists of sedimentary limestone with scattered chert beds, including th ...

that was exposed in a quarry near the town of Sigourney and dates to the

Viséan The Visean, Viséan or Visian is an age in the ICS geologic timescale or a stage in the stratigraphic column. It is the second stage of the Mississippian, the lower subsystem of the Carboniferous. The Visean lasted from to Ma. It follows the ...

stage, making it approximately 335 million years old. Bolt and Lombard named the genus after Sigourney. The species name ''multidentata'' alludes to the many teeth preserved in the jaw. The jaw, which is housed in the

Field Museum The Field Museum of Natural History (FMNH), also known as The Field Museum, is a natural history museum in Chicago, Illinois, and is one of the largest such museums in the world. The museum is popular for the size and quality of its educational ...

and cataloged as FM PR 1820, curves strongly downward but was probably straight to begin with, having been deformed by the process of fossilization after the individual died. Rooted in the

dentary bone In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable ...

along the outermost edge of the jaw are 88 small, pointed marginal teeth. An additional row of even smaller teeth runs along the coronoids, three bones positioned lengthwise along the lower boundary of the dentary on the inner surface of the lower jaw. Bolt and Lombard were able to classify ''Sigournea'' as an early member of Tetrapoda based on the presence of bone surfaces covered in pits and ridges, a single row of dentary teeth, a jaw joint that faces upward, and an open groove for a lateral line along the outer surface of the jaw, and on the absence of teeth on the prearticular bone or enlarged fangs on the coronoids. ''Sigournea'' differs from other stem tetrapods in having several holes within a depression called the exomeckelian fenestra on the inner surface of the jaw. The closest relatives of ''Sigournea'' within Tetrapoda are unknown. Bolt and Lombard did not include it in a

phylogenetic analysis In biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that pro ...

in their 2006 description because they thought the single known jawbone did not possess enough unique anatomical characteristics to elucidate its evolutionary relationships. However, in 2008, Bolt and his colleague

Marcello Ruta Marcello Ruta is an Italian paleontologist. Ruta's research primarily has focused on the anatomy and evolutionary significance of Paleozoic tetrapods. Selected publications *Ruta, M., Coates, M. I. and Quicke, D. L. J. 2003. Early tetrapo ...

published a phylogenetic analysis that did include ''Sigournea'', and found good support for ''S. multidentata'' grouping with ''

Occidens portlocki ''Occidens'' is an extinct genus of stem tetrapod that lived during the earliest part of the Carboniferous in what is now Northern Ireland. It is known from a single type species, ''Occidens portlocki'', named in 2004 on the basis of a left low ...

'', a species of stem tetrapod named in 2004 from the earliest Carboniferous (

Tournaisian The Tournaisian is in the ICS geologic timescale the lowest stage or oldest age of the Mississippian, the oldest subsystem of the Carboniferous. The Tournaisian age lasted from Ma to Ma. It is preceded by the Famennian (the uppermost stag ...

) of Northern Ireland. Milner ''et al.'' (2009) suggested that ''Sigournea'' may be a close relative of the slightly younger

baphetoid Baphetoidea is a superfamily of early tetrapods. It includes the family Baphetidae and several more basal genera such as ''Eucritta'' and ''Spathicephalus'' (which has been given its own family Spathicephalidae). The superfamily has also been cal ...

tetrapod ''

Spathicephalus ''Spathicephalus'' is an extinct genus of stem tetrapods (early four-limbed vertebrates) that lived during the middle of the Carboniferous Period. The genus includes two species: the type species ''S. mirus'' from Scotland, which is known from t ...

'' from Scotland and Nova Scotia based on the presence of small, closely packed marginal teeth in both taxa. However, their proposition was tentative because they did not include ''Sigournea'' in their phylogenetic analysis.

References

{{Taxonbar, from=Q18358603 Carboniferous tetrapods Prehistoric tetrapod genera Paleozoic animals of North America