Pterosaurs - Pterosaurs

A reptile that invaded the skies during the Mesozoic era. Subclass: Diapsidae, subclass: Archosaur, order: Pterosaur. Unlike birds and bats, the fourth finger on the hand was long and long, split into four parts, and had leathery wings. The remaining fingers were small and formed hook-like claws, which were likely used to hang from rocks and branches. The bones were light and hollow like birds', but strong. The sternum was large, and had muscles that moved the wings. Because the pelvis was small, it was thought that the reptile probably laid eggs, and the eggs were small, but in 2004, the first egg fossils were discovered in strata from the Early Cretaceous period in Argentina and China. Both were oval in shape, about 6 cm long and 2 to 3.5 cm wide. They may have lived in large flocks near coastal cliffs, riding the rising air currents during the day and hiding in the shade of rocks at dusk, hanging head-down like a bat and sleeping. If the membranes on their wings were torn, they would have been unable to fly.

The primitive Rhamphorhynchoidea suborder appeared in the Late Triassic and became extinct at the end of the Jurassic. Its representative genus was the Late Jurassic Rhamphorhynchus , which had a short neck and long tail, was small, had a long, slender snout with thin teeth, and likely ate fish. The more advanced Pterodactyloidea suborder appeared in the Late Jurassic and became extinct at the end of the Cretaceous. They were generally large. The Late Cretaceous Pteranodon had a wingspan of 8 meters, a slender skull that extended backwards, and a long, toothless beak. The Pterodactylus lived from the Late Jurassic to the Early Cretaceous, but was only about 20 centimeters long, had a short tail, and wide wings. It had a few small, thin teeth in the front of its jaw. Pterosaurs have diverse jaws and teeth that differ depending on the genus, and their feeding habits vary, with their diet apparently varying from fish, shellfish, plankton, nuts, and carrion. Their aerodynamic characteristics are more similar to those of frigatebirds and gliders. They may have been homeothermic. Pterosaurs have also been reported in Japan from the Cretaceous layers of Hokkaido, Honshu, and Kyushu.

[Ikuo Obata]

"Pterosaurs" by Peter Wellnhofer, translated by Watanabe Masataka (Encyclopedia of Animals, Supplementary Volume 2, 1993, Heibonsha) " "Mechanics of Pterosaurs" by Sugimoto Tsuyoshi (included in Dinosaur Studies, edited by Obata Ikuo, 1993, University of Tokyo Press) " "The Mystery of Pterosaurs - The Age of Pterosaurs, Plesiosaurs, and Ichthyosaurs" by Kaneko Ryuichi, Nakano Mika, and Nagao Eriko (1995, Futami Shobo)

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

中生代の空に進出した爬虫(はちゅう)類。双弓(そうきゅう)亜綱主竜下綱翼竜目。鳥やコウモリと違って、手の4番目の指が長く伸びて四つの部分にくぎれ、皮の翼が張られていた。残りの指は小さくて、鉤(かぎ)状のつめをなし、岩や大枝にぶら下がるのに使われたらしい。骨は鳥のように軽く中空で、しかしじょうぶであった。胸骨が大きく、それには翼を動かす筋肉がついていた。骨盤が小形なので、たぶん卵生で卵も小さかったと考えられていたが、2004年になって、アルゼンチンと中国の白亜紀前期の地層から、初めて卵化石が発見された。ともに楕円(だえん)形で、縦約6センチメートル、横約2～3.5センチメートルであった。海岸の崖(がけ)に近い所で大きな群れをなして生活し、昼は上昇気流にのり、夕暮れには岩陰などを隠れ場所とし、コウモリのように頭を下向きにぶら下がって眠ったのかもしれない。翼の膜が破れると飛べなくなったであろう。

　原始的なランフォリンクス亜目Rhamphorhynchoidea（ランフォリンクス類）は三畳紀後期に出現し、ジュラ紀末に絶滅した。その代表属はジュラ紀後期のランフォリンクスRhamphorhynchusで、短い頸(くび)と長い尾をもち、小形で、細長い吻部(ふんぶ)に細い歯があり、魚を食べたらしい。進んだタイプのプテロダクチルス亜目Pterodactyloidea（プテロダクチルス類）はジュラ紀後期に現れ、白亜紀末に絶滅した。一般に大形である。白亜紀後期のプテラノドンPteranodonは翼を広げると8メートルもあり、頭骨は細長く後ろに伸び、長いくちばしには歯がない。プテロダクチルスPterodactylusはジュラ紀後期から白亜紀前期にいたが、全長約20センチメートルしかなく、尾が短く翼が広い。あごの前部に小さな薄い歯がすこしばかりついている。翼竜は属によってあごと歯が多様に分化しており食性もさまざまで、食餌(しょくじ)も魚や貝、プランクトン、木の実、死肉と違っていたらしい。空気力学的特性は、むしろグンカンドリやグライダーに近い。恒温性を獲得していた可能性がある。翼竜は日本でも北海道、本州、九州の白亜紀層から産出が報じられている。

［小畠郁生］

『ペーター・ヴェルンホファー著、渡辺政隆訳『翼竜』（『動物大百科　別巻2』1993・平凡社）』▽『杉本剛著「翼竜の力学」（小畠郁生編『恐竜学』所収・1993・東京大学出版会）』▽『金子隆一・中野美鹿・長尾衣里子著『翼竜の謎――翼竜・首長竜・魚竜の時代』（1995・二見書房）』

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