直角石

直角石（學名：）是一屬已滅絕的鸚鵡螺類。其化石在歐洲非常普遍。牠們在海中是活躍的泳者，游泳時殼呈水平狀，以觸手捕捉小動物為食。

特徵
直角石的殼形為細長的柱狀椎體，稱為「直角石式殼」（orthoceracone），由間距緊密的凹凸殼室組成。 ==
*Orthoceras annulata Sowerby, 1818
*Orthoceras bisignatum Barrande, 1877
*Orthoceras blakei Gabb, 1864
*Orthoceras burgense Gemmellaro, 1889
*Orthoceras decrescens de Koninck, 1863
*Orthoceras dominans de Gregorio, 1930
*Orthoceras elegantulum Gemmellaro, 1889
*Orthoceras expansum Blake, 1882
*Orthoceras fluminense Meneghini, 1857
*Orthoceras geinitzi d'Orbigny, 1850
*Orthoceras gradatum Gemmellaro, 1889
*Orthoceras hulli Gemmellaro, 1889
*Orthoceras lentum Ruedemann, 1906
*Orthoceras lepton Gemmellaro, 1889
*Orthoceras luhai Stumbur, 1956
*Orthoceras modestum Ruedemann, 1906
*Orthoceras oehlerti Gemmellaro, 1889
*Orthoceras orientale Fliegel, 1901
*Orthoceras progressum Ruedemann, 1906
*Orthoceras punjabiense Waagen, 1879
*Orthoceras rachidium de Koninck, 1863
規則直角石 Orthoceros regularis* Schlotheim, 1820
*Orthoceras shastense Hyatt & Smith, 1905
*Orthoceras siculum Gemmellaro, 1889
*Orthoceras spissiseptum Dwight, 1884
*Orthoceras submoniliforme Meneghini, 1857
*Orthoceras subtriangulare Gemmellaro, 1889
*Orthoceras vagum Ruedemann, 1906
*Orthoceras vesiculosum de Koninck, 1863
*Orthoceras waageni Gemmellaro, 1889
*Orthoceratites Lamarck, 1799

參考文獻
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外部連結

• [http://paleodb.org/cgi-bin/bridge.pl?action=basicTaxonInfo&taxon_no=12557 Orthoceras] in the Paleobiology Database

*[https://web.archive.org/web/20081216220615/http://english.fossiel.net/system/glossarium/orthoceras.jpg 直角石的相片]，fossiel.net

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