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Psephosauriscus
''Psephosauriscus'' is an extinct genus of placodont reptile from the Middle Triassic of Israel and Egypt. It is known from bony armor plates that have been found from Makhtesh Ramon in Israel's Negev desert and Araif en Naqua on Egypt's Sinai Peninsula. The genus was erected in 2002 as a replacement name for several species of the genus ''Psephosaurus'', which was named in 1957. It includes the species ''P. mosis'', ''P. ramonensis'', ''P. sinaiticus'', and a possible fourth species, ''P. rhombifer''. All species, with the exception of ''P. ramonensis'', were once assigned to the genus ''Psephosaurus''. Remains of ''P. mosis'' and ''P. ramonensis'' were found in Makhtesh Ramon, while ''P. sinaiticus'' and ''P. rhombifer'' were found in Araif en Naqua.
==History==
Armor of ''Psephosauriscus'' is abundant in Middle Triassic limestone in the Sinai and Negev regions, which is comparable to the Muschelkalk of European rock sequences. While the German Muschelkalk contains many nearly complete skeletons of placodonts, the only non-armor skeletal bones from the Middle East are two partial skulls and a fragmentary lower jaw, which cannot be assigned to ''Psephosauriscus'' or any other placodont because of their lack of diagnostic features. Remains of ''Psephosauriscus'' come from two deposits called the ''Beneckeia'' beds and the ''Ceratites'' beds, named after their most common ammonite fossils. The ''Beneckeia'' beds date back to the Anisian stage of the Middle Triassic, and the ''Ceratites'' beds date back to the end of the Anisian and beginning of the Ladinian stage.〔
Swedish paleontologist F. Brotzen described placodont armor from Makhtesh Ramon in 1957, naming the species ''Psephosaurus mosis'' and ''Psephosaurus picardi'' from the ''Beneckeia'' and ''Ceratites'' beds, respectively. ''P. picardi'' is now considered a ''nomen dubium'' because it was based on an impression of the inner surface of the carapace that did not possess any distinct features. In 1959, Austrian paleontologist Georg Haas named ''P. sinaiticus'' and ''P. rhombifer'' from Araif en Naqua.〔
In 2002, paleontologist Olivier Rieppel erected the genus ''Psephosauriscus'' to include most of the species named by Brotzen and Haas, which he considered distinct from the type species of ''Psephosaurus'', ''P. suevicus'', named by Eberhard Fraas from the Middle Triassic of Germany. Rieppel noted differences between the armor plates of ''P. suevicus'' and the Middle Eastern species that warranted a new genus. However, ''P. rhombifer'' could not be assigned with certainty to ''Psephosauriscus'' because the holotype specimen described by Haas had since been lost. Rieppel reported additional material from Araif en Naqua that showed similarities to ''P. rhombifer'' and the species of ''Psephosauriscus'', which he tentatively described as a species within ''Psephosauriscus'', ''Psephosauriscus cf. rhombifer''. Rieppel also named ''Psephosauriscus ramonensis'' as an entirely new species.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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