Rhabdognathus

Rhabdognathus is an extinct genus of dyrosaurid crocodylomorph. It is known from rocks dating to the Paleocene epoch from western Africa,[1] and specimens dating back to the Maastrichtian era were identified in 2008.[2] It was named by Swinton in 1930 for a lower jaw fragment from Nigeria.[3] The type species is Rhabdognathus rarus.[3] 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.[3] The genus formerly contained the species Rhabdognathus compressus, which was reassigned to Congosaurus compressus after analysis of the lower jaw of a specimen found that it was more similar to that of the species Congosaurus bequaerti.[3] Rhabdognathus is believed to be the closest relative to the extinct Atlantosuchus.[4]

Rhabdognathus
Temporal range: Late CretaceousPaleocene
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Family: Dyrosauridae
Genus: Rhabdognathus
Swinton, 1930
Species
  • R. rarus Swinton, 1930 (type)
  • R. aslerensis Jouve, 2007
  • R. keiniensis Jouve, 2007

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 73.1 centimetres (28.8 in), 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.[5][6] The mandible 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, which extends past the nineteenth mandibular alveolus. The splenial 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.[3]

The skulls of R. aslerensis and R. keiniensis possess numerous characters that distinguish Rhabdognathus from other dyrosaurids. The posterior wall of the supratemporal fenestra 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.[7] In both species of Rhabdognathus, the space between the occipital condyle 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.[3]

References

  1. ^ New Long-Snouted Dyrosaurid (Crocodylomorpha, Mesoeucrocodylia) from the Paleocene of Northeastern Colombia. Hastings, Alexander, University of Florida, Gainesville, FL, USA; Bloch, Jonathan, Florida Museum of Natural History, Gainesville, FL, USA. [1]
  2. ^ Dyrosaurid (Crocodyliformes, Mesoeucrocodylia) fossils from the Upper Cretaceous and Paleogene of Mali : implications for phylogeny and survivorship across the K-T boundary. American Museum Novitates, no. 3631. Hill, Robert V., McCartney, Jacob A., Roberts, Eric M., Bouaré, Mohamed L., Sissoko, Famory., O'Leary, Maureen Ann. 2008. [2].
  3. ^ a b c d e f Jouve, Stephane (2007). "Taxonomic revision of the Dyrosaurid Assemblage (Crocodyliformes: Mesoeucrocodylia) from the Paleocene of the Iullemmeden basin, west Africa". Journal of Paleontology. 81 (1): 163–175. doi:10.1666/0022-3360(2007)81[163:TROTDA]2.0.CO;2.
  4. ^ 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.
  5. ^ Hastings, A. K; Bloch, J. I.; Cadena, E. A.; Jaramillo, C. A. (2010). "A new small short-snouted dyrosaurid (Crocodylomorpha, Mesoeucrocodylia) from the Paleocene of northeastern Colombia". Journal of Vertebrate Paleontology. 30 (1): 139–162. doi:10.1080/02724630903409204.
  6. ^ Brochu, C. A.; Bouaré, M. L.; Sissoko, F.; Roberts, E. M.; O'Leary, M. A. (2002). "A dyrosaurid crocodyliform braincase from Mali". Journal of Paleontology. 76 (6): 1060–1071. doi:10.1666/0022-3360(2002)076<1060:ADCBFM>2.0.CO;2.
  7. ^ Jouve, S. (2005). "A new description of Dyrosaurus phosphaticus (Thomas, 1893) (Mesoeucrocodylia: Dyrosauridae) from the Lower Eocene of North Africa". Canadian Journal of Earth Sciences. 42 (3): 323–337. doi:10.1139/e05-008.

External links

Acherontisuchus

Acherontisuchus is an extinct genus of dyrosaurid neosuchian from Middle to Late Paleocene deposits of Colombia. The only known species is A. guajiraensis, whose name means "Acheron crocodile of the Guajira Peninsula".

Aegyptosuchidae

Aegyptosuchidae is an extinct family of eusuchian crocodyliforms from the Cretaceous period of Africa. They are characterized by their large size and flat heads. The family includes two genera, Aegyptosuchus and Aegisuchus.

Amphicotylus

Amphicotylus is an extinct genus of goniopholidid mesoeucrocodylian from the Tithonian of Colorado and Oklahoma.

Atlantosuchus

Atlantosuchus is an extinct genus of dyrosaurid crocodylomorph from Morocco. One defining characteristic that distinguishes it from other long-snouted dyrosaurids was its proportionally elongate snout, the longest in proportion to body size of any dyrosaurid. Rhabdognathus, a hyposaurine dyrosaurid, is believed to have been the closest relative of the genus.

Brillanceausuchus

Brillanceausuchus is an extinct genus of atoposaurid crocodylomorph. Fossils have been found in Early Cretaceous–age rocks of Cameroon. The genus is notable for the position of the secondary choana within its palate. Parts of the pterygoid bones make up the rostral margin of the choana and thus separate it from the palatines, a feature also seen in the more advanced neosuchian suborder Eusuchia. This characteristic was once thought to be characteristic of Eusuchia, but its presence in Brillanceausuchus suggests that the trait is homoplasic, thus making the evolution of the position of the choana within crocodilians more complex than previously thought.

Cerrejonisuchus

Cerrejonisuchus is an extinct genus of dyrosaurid crocodylomorph. It is known from a complete skull and mandible from the Cerrejón Formation in northeastern Colombia, which is Paleocene in age. Specimens belonging to Cerrejonisuchus and to several other dyrosaurids have been found from the Cerrejón open-pit coal mine in La Guajira. The length of the rostrum is only 54-59% of the total length of the skull, making the snout of Cerrejonisuchus the shortest of all dyrosaurids.

Coelosuchus

Coelosuchus is an extinct genus of goniopholidid mesoeucrocodylian. Fossils have been found from the Graneros Shale of the Benton Group in Wyoming, and are of Cenomanian age. It was slightly over 1 meter in length.

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 genus was later thought synonymous with Hyposaurus in 1976 and 1980. It has since been proven a distinct genus of dyrosaurid separate from both Dyrosaurus and Hyposaurus.In 2007, a new species of Congosaurus was constructed after previously being assigned to Rhabdognathus, and named C. compressus, extending the geographic range of the genus into the present-day Sahara. Lateromedially compressed teeth show its close relation to C. bequaerti.

Dyrosauridae

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 America. Over a dozen species are currently known, varying greatly in overall size and cranial shape. All were presumably aquatic, with species inhabiting both freshwater and marine environments. Ocean-dwelling dyrosaurids were among the few marine reptiles to survive the Cretaceous–Paleogene extinction event.

Eusuchia

The Eusuchia ("true crocodiles") are a clade of crocodylomorphs that first appears in the Early Cretaceous with Hylaeochampsa. Along with Dyrosauridae and Sebecosuchia, they were the only crocodyliformes who survived the K-T extinction. Since the other two clades died out 35 and 11 million years ago, all living crocodilian species are eusuchians, as are many extinct forms.

Karatausuchus

Karatausuchus is an extinct genus of atoposaurid crocodylomorph. It is known from a single specimen discovered in the Late Jurassic (Oxfordian - Kimmeridgian) Karabastau Svita from the vicinity of Mikhailovka in the Karatau Mountains of southern Kazakhstan. The type specimen is PIN 25858/1, a complete but poorly preserved juvenile skeleton with some possible soft tissue preservation. It is notable for having over 90 teeth, but its other anatomical details are difficult to discern. The length of this individual is estimated at 160 millimetres (6.3 in). Karatausuchus was described in 1976 by Mikhail Efimov, and the type species is K. sharovi.

Khoratosuchus

Khoratosuchus is an extinct genus of neosuchian crocodylomorph which existed in northeast Thailand during the early Cretaceous period. Its type species is Khoratosuchus jintasakuli. Khoratosuchus is the youngest and most advanced Mesozoic crocodyliform yet known from Thailand. It possesses several distinctive features that help determine its phylogenetic position among crocodylomorphs, including secondary choanae relatively posterior and almost encircled by the pterygoid bones on the palate and a smooth dorsal surface of the skull.

Nannosuchus

Nannosuchus (meaning "dwarf crocodile") is an extinct genus of goniopholidid mesoeucrocodylian from the Berriasian of England.

Neosuchia

Neosuchia is a clade within Mesoeucrocodylia that includes all modern extant crocodilians and their closest fossil relatives. It is defined as the most inclusive clade containing all crocodylomorphs more closely related to Crocodylus niloticus (the Nile Crocodile) than to Notosuchus terrestris. Neosuchia is very diverse and may be polyphyletic, as the clade has undergone many revisions since it was first named in 1988. Neosuchians first appear in the Early Jurassic with the earliest known goniopholid Calsoyasuchus, which lived during the Sinemurian and Pliensbachian stages.

Pholidosauridae

Pholidosauridae is an extinct family of aquatic neosuchian mesoeucrocodylian crocodylomorphs. Fossils have been found in Europe (Denmark, England, France, Germany, Spain and Sweden), Africa (Algeria, Niger, Mali, Morocco and Tunisia), North America (Canada and the United States) and South America (Brazil and Uruguay). The pholidosaurids first appeared in the fossil record during the Bathonian stage of the Middle Jurassic and became extinct during the Late Turonian stage of the Late Cretaceous.Sarcosuchus is one of the best known pholidosaurs. It is believed to have attained lengths of up to 12 metres (39 ft 4 in) and weighed up to 8 tonnes (7.9 long tons; 8.8 short tons). One genus, Suchosaurus, once thought to be a pholidosaur, has since been shown to be a spinosaurid theropod dinosaur.

Phosphatosaurus

Phosphatosaurus is an extinct genus of dyrosaurid crocodylomorph. It existed during the early Eocene, with fossils having been found from North Africa in Tunisia and Mali. Named in 1955, Phosphatosaurus is a monotypic genus; the type species is P. gavialoides. A specimen has been discovered from Niger, but it cannot be classified at the species level.Phosphatosaurus is closely related to the Cretaceous genus Sokotosuchus, which is known from Niger and Mali. Because Phosphatosaurus is only known from Paleogene localities, the close relationship with Sokotosuchus implies that there is a long ghost lineage extending back into the Maastrichtian that is not known in the fossil record.

Symptosuchus

Symptosuchus is an extinct genus of goniopholidid mesoeucrocodylian. It is known from the Late Cretaceous of Argentina. Argentine paleontologist Florentino Ameghino named the genus in 1899, along with the type species S. contortidens. It was formally described by Carlos Rusconi in 1934.

Wahasuchus

Wahasuchus is a genus of extinct mesoeucrocodylian of the Middle Campanian age found in the Quseir Formation, Egypt. The generic name derives from the Arabic word واحة (waha), which means "oasis", and souchos from the Greek in honor of crocodile-headed god of ancient Egypt. The specific egyptensis (Lat.) means from Egypt.Fossils of skull and jaw fragments, dorsal vertebrae, and fragmentary appendicular remains have been recovered.

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