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''Eosuchus'' (Dawn Crocodile) is an extinct genus of gavialoid crocodilian. It is among the most basal of all gavialoids, lying crownward of all other known members of the superfamily, including earlier members such as ''Thoracosaurus'' and ''Eothoracosaurus''. Fossils have been found from France as well as eastern North America in Maryland, Virginia, and New Jersey. The strata from which specimens have been found date back to the late Paleocene and early Eocene epochs. ==Species== The name ''Eosuchus'' was first used in 1907 to describe a single specimen found from northern France near the Belgian border, assigned to the type species ''E. lerichei''.〔Dollo, L. (1907). Les reptiles de l'Éocène Inférieur de la Belgique et des régions voisines. ''Bulletin de la Societe Belge de Géologie, de Paléontologie et d'Hydrologie'' 21:81-85.〕 A second species, ''E. minor'', was named in 2006 from material found from the United States, having been referred in the past to several different genera of crocodilians. ''E. minor'' differs from ''E. lerichei'' on the basis of a noticeably wider nasal and prefrontals positioned anteriorly further up the skull than the lacrimals A new species of ''Gavialis'', ''G. minor'', was named by Othniel Charles Marsh in 1870 on the basis of the holotype specimen YPM 282, consisting of cranial fragments and isolated vertebrae found from the Manasquan Formation in Monmouth County, New Jersey. The locality dates back to the Ypresian stage of the early Eocene. The species name refers to the relatively small estimated size of the animal, estimated at no more than 2 meters, when compared to other gavialoids such as the modern gharial, which can grow up to 5 meters in length. However, this species was later recognized as distinct from ''Gavialis'' on the basis of certain aspects of the known cranial material, in particular the large foramen aerum of the quadrate formed from the epithelial tube that connects the pneumatic chambers of the quadrate and articular. Another diagnostic feature thought to distinguish the species from ''Gavialis'' was the narrow interfenestral bar of the parietal bone that is relatively smooth and unsculptured when compared to other gavialoids such as ''Thoracosaurus''. The name ''Thecachampsoides'' was proposed for the species ''G. minor'' in 1986.〔Norell, M. A., and Storrs, G. W. (1986). Catalogue and review of the type fossil crocodilians in the Yale Peabody Museum. ''Postula'' 203:1-28.〕 A close relationship between ''T. minor'' and ''Eosuchus lerichei'' was always evident, yet it was not until 2006 that the name ''Eosuchus'' was applied to the ''T. minor'' specimens, specifically on the basis of a fairly complete specimen called NJSM 15437 from the Vincetown Formation in New Jersey, of which there is a visibly exposed braincase which aids greatly in the taxonomic classification of the genus. The examination of specimens of ''T. minor'' with those of ''E. lerichei'' yielded many similarities between the two species, including the foramen aerum as well as other features such as a long nasal process between the premaxillae, dentary alvioli arranged in pairs, and a W-shaped basioccipital tuberosity.〔Brochu, C. A. (2006) Osteology and phylogenetic significance of Eosuchus minor(Marsh, 1870) new combination, a longirostrine crocodylian from the Late Paleocene of North America. ''Journal of Paleontology'' 80(1):162-186.〕 Other material present from the Aquia Formation of Maryland and Virginia, which dates back to the early Paleocene, tends to be more complete. Some specimens found from these localities are known from nearly complete skulls that provide a more detailed view of the phylogenetic position of ''Eosuchus'', and further aid in distinguishing ''E. minor'' from other gavialoids. Historically, many other species of extinct gavialoids have been assigned to the genus ''Gavialis'' (of which the modern gharial, ''G. gangeticus'', is a member of). These include forms such as ''Thoracosaurus''. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Eosuchus」の詳細全文を読む スポンサード リンク
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