''Letognathus'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

rhizodont Rhizodontida is an extinct group of predatory tetrapodomorphs known from many areas of the world from the Givetian through to the Pennsylvanian - the earliest known species is about 377 million years ago (Mya), the latest around 310 Mya. Rhizod ...

tetrapodomorph Tetrapodomorpha (also known as Choanata) is a clade of vertebrates consisting of tetrapods (four-limbed vertebrates) and their closest sarcopterygian relatives that are more closely related to living tetrapods than to living lungfish. Advanced for ...

that lived during the

Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...

period. Its remains come from the Blue Beach Member of the Horton Bluff Formation, near Hantsport,

Nova Scotia Nova Scotia is a Provinces and territories of Canada, province of Canada, located on its east coast. It is one of the three Maritime Canada, Maritime provinces and Population of Canada by province and territory, most populous province in Atlan ...

. Like most rhizodonts, it was of relatively large size, had a large recurved fang at the symphysis of the lower jaw, and a row of three coronoid fangs along the length of the jaw in addition to its marginal dentition. ''Letognathus'' is important for rhizodont systematics because it retains a number of primitive features, such as ossified

Meckel's cartilage In humans, the cartilaginous bar of the mandibular arch is formed by what are known as Meckel's cartilages (right and left; also known as Meckelian cartilages), above which the incus and malleus are located. Meckel's cartilage arises from the fir ...

, are not found in the genera ''

Rhizodus ''Rhizodus'' ("root tooth") is an extinct genus of basal, finned tetrapodomorphs (the group of sarcopterygians that contains modern tetrapods and their extinct relatives). It belonged to Rhizodontida, one of the earliest-diverging tetrapodomorph ...

'' and '' Strepsodus''.

Taxonomic History

The members of the Rhizodontida have nearly all had complex taxonomic historiesJeffery, J.E. 2006. The Carboniferous fish genera ''Strepsodus'' and ''Archichthys'' (Rhizodontida: Sarcopterygii): clarifying 150 years of confusion. ''Palaeontology'' 49: 113-132 due to earlier use of the genus ''Strepsodus'' as a

wastebasket taxon Wastebasket taxon (also called a wastebin taxon, dustbin taxon or catch-all taxon) is a term used by some taxonomists to refer to a taxon that has the purpose of classifying organisms that do not fit anywhere else. They are typically defined by e ...

. The taxon was originally assigned to the genus ''

'' by

John William Dawson Sir John William Dawson (1820–1899) was a Canadian geologist and university administrator. Life and work John William Dawson was born on 13 October 1820 in Pictou, Nova Scotia, where he attended and graduated from Pictou Academy. Of Sco ...

and later to '' Strepsodus'' by

Arthur Smith Woodward Sir Arthur Smith Woodward, FRS (23 May 1864 – 2 September 1944) was an English palaeontologist, known as a world expert in fossil fish. He also described the Piltdown Man fossils, which were later determined to be fraudulent. He is not rel ...

. A new genus was erected for the Horton Bluff material based on a number of differences from either ''Strepsodus'' or ''Rhizodus''.

References

Rhizodontida Mississippian sarcopterygians of North America {{paleo-tetrapodomorph-stub