''Rhabdognathus'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

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 ...

dyrosaurid Dyrosauridae is a family (biology), family of extinct neosuchian crocodyliforms that lived from the Campanian to the Eocene. Dyrosaurid fossils are globally distributed, having been found in Africa, Asia, Europe, North America and South America. ...

crocodylomorph Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction. Extinct crocodylomorphs were considerably mor ...

. It is known from rocks dating to the

Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...

epoch from western

Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...

, and specimens dating back to the

Maastrichtian The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stage (stratigraphy), stage) of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (s ...

era were identified in 2008. It was named by Swinton in 1930 for a lower jaw fragment from

Nigeria Nigeria, officially the Federal Republic of Nigeria, is a country in West Africa. It is situated between the Sahel to the north and the Gulf of Guinea in the Atlantic Ocean to the south. It covers an area of . With Demographics of Nigeria, ...

. The type species is ''Rhabdognathus rarus''. Stéphane Jouve subsequently assessed ''R. rarus'' as indeterminate at the species level, but not at the genus level, and thus dubious. Two skulls which were assigned to the genus ''Rhabdognathus'' but which could not be shown to be identical to ''R. rarus'' were given new species: ''R. aslerensis'' and ''R. keiniensis'', both from

Mali Mali, officially the Republic of Mali, is a landlocked country in West Africa. It is the List of African countries by area, eighth-largest country in Africa, with an area of over . The country is bordered to the north by Algeria, to the east b ...

. The genus formerly contained the species ''Rhabdognathus compressus'', which was reassigned to ''

Congosaurus ''Congosaurus'' is an extinct genus of dyrosaurid mesoeucrocodylian. Fossils have been found from Lândana, in Angola and date back to the Paleocene epoch. In 1952 and 1964 ''Congosaurus'' was proposed to be synonymous with '' Dyrosaurus''. The g ...

compressus'' after analysis of the lower jaw of a specimen found that it was more similar to that of the species ''Congosaurus bequaerti''. ''Rhabdognathus'' is believed to be the closest relative to the extinct '' Atlantosuchus''.Jouve, S., B. Bouya, and M. Amaghzaz (2008). A long-snouted dyrosaurid (Crocodyliformes, Mesoeucrocodylia) from the Paleocene of Morocco: phylogenetic and palaoebiogeographic implications. Palaeontology 51(2):281-294.

Description

''Rhabdognathus'' has an extremely elongated snout that makes up around 75% of the length of the entire skull. The total skull length of ''R. keiniensis'' is , while the length of the skull of ''R. aslerensis'' is unknown because the front of the snout is not preserved in the only known skull, CNRST-SUNY-190. The

mandible In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

of ''Rhabdognathus'' is as high as it is wide or higher, which distinguishes it from ''Hyposaurus''. The mandible is dorsally directed toward the tip, and the first pair of alveoli (tooth sockets) at the very tip of the jaw are higher than the others. Another distinguishing feature is the extreme length of the mandibular

symphysis A symphysis (, : symphyses) is a fibrocartilaginous fusion between two bones. It is a type of cartilaginous joint, specifically a secondary cartilaginous joint. # A symphysis is an amphiarthrosis, a slightly movable joint. # A growing together o ...

, which extends past the nineteenth mandibular alveolus. The

splenial The splenial is a small bone in the lower jaw of reptile Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology ...

also extends beyond this point, although the position of its symphysis varies during growth. The alveoli of ''Rhabdognathus'' are rounded and directed slightly laterally, causing the teeth to project at an angle. The skulls of ''R. aslerensis'' and ''R. keiniensis'' possess numerous characters that distinguish ''Rhabdognathus'' from other dyrosaurids. The posterior wall of the

supratemporal fenestra Temporal fenestrae are openings in the temporal region of the skull of some amniotes, behind the orbit (eye socket). These openings have historically been used to track the evolution and affinities of reptiles. Temporal fenestrae are commonly (al ...

inclines dorsally so that it is visible when the skull is viewed in dorsal aspect. In ''Dyrosaurus phosphaticus'', the wall is vertical and thus not visible in dorsal aspect. In both species of ''Rhabdognathus'', the space between the

occipital condyle The occipital condyles are undersurface protuberances of the occipital bone in vertebrates, which function in articulation with the superior facets of the Atlas (anatomy), atlas vertebra. The condyles are oval or reniform (kidney-shaped) in shape ...

and the basioccipital tubera (both located in the back of the skull where the vertebrae articulate) is anteroposteriorly longer than in ''D. phosphaticus''. In the skulls of both species of ''Rhabdognathus'', the posterior margin is inclined so that both the occipital condyle and the basioccipital tubera below it are visible in occipital view.

References

External links

''Rhabdognathus''
at the

Paleobiology Database The Paleobiology Database (PBDB) is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms. History The Paleobiology Database originated in the NCEAS-funded Phanerozoic Marine Pale ...

{{Taxonbar, from=Q2248943 Late Cretaceous crocodylomorphs of Africa Paleocene crocodylomorphs Prehistoric pseudosuchian genera Prehistoric marine crocodylomorphs Paleocene reptiles of Africa Dyrosauridae Fossils of Mali