''Rhabdognathus'' is an extinct

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 ...

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

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. During Mesozoic and early Cenozoic times, cro ...

. It is known from rocks dating to the

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

epoch from western

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

, and specimens dating back to the

Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interv ...

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

Nigeria Nigeria ( ), , ig, Naìjíríyà, yo, Nàìjíríà, pcm, Naijá , ff, Naajeeriya, kcg, Naijeriya 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 G ...

. 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 Doubt is a mental state in which the mind remains suspended between two or more contradictory propositions, unable to be certain of any of them. Doubt on an emotional level is indecision between belief and disbelief. It may involve uncertainty ...

. 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,, , ff, 𞤈𞤫𞤲𞥆𞤣𞤢𞥄𞤲𞤣𞤭 𞤃𞤢𞥄𞤤𞤭, Renndaandi Maali, italics=no, ar, جمهورية مالي, Jumhūriyyāt Mālī is a landlocked country in West Africa. Ma ...

. 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 ...

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 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 bon ...

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 (, pl. 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 togethe ...

, which extends past the nineteenth mandibular alveolus. The

splenial The splenial is a small bone in the lower jaw of reptiles, amphibians and birds, usually located on the lingual side (closest to the tongue) between the angular and surangular The suprangular or surangular is a jaw bone found in most land ve ...

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 The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

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 vertebra. The condyles are oval or reniform (kidney-shaped) in shape, and their anteri ...

and the

basioccipital tubera The basilar part of the occipital bone (also basioccipital) extends forward and upward from the foramen magnum, and presents in front an area more or less quadrilateral in outline. In the young skull this area is rough and uneven, and is joined t ...

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

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